thesis on polymers from bacterial sources

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Thesis on polymers from bacterial sources

RESUME LANDSCAPE ORIENTATION

PHA-producing genes exist in various bacteria. Although these genes are dispersed on chromosome in some organisms, they are in tandem in other bacteria such as R. Although the capacity of R. Hence, many efforts have been accomplished to create recombinant bacteria and use economic carbon sources. In a report by Galehdari et al. In their study, three types of recombinant E. In our study, the whole operon of PHB was extracted and an expression vector was constructed; then, the production of PHB was confirmed in the recombinant bacteria.

Many other reports used phb genes from R. The high-yield production of PHB in natural PHA-producing bacteria can be reduced by high activity of intracellular depolymerase. To overcome this bottleneck, metabolically-engineered E. Intensive efforts are being made to reduce the cost of production by means of bioprocess designing and metabolic engineering of the production strains 2. In this study, we successfully cloned and expressed the recombinant pETa containing the PHB-biosynthesis genes.

PHB granules were observed in E. In Sudan Black B staining, lipid inclusion granules were stained blue-black or blue-grey, whilst the bacterial cytoplasm was stained light pink. Therefore, PHB was produced from the recombinant E. Authors' Contributions: This work is part of the Master thesis of Maryam Jari and she wrote the paper.

Saeid Reza Khatami was the supervisor of the thesis and edited the manuscript. Hamid Galehdari was the co-supervisor of the thesis. Mohammad Shafiei was the adviser of the thesis. All the authors read and approved the final manuscript. National Center for Biotechnology Information , U. Journal List Jundishapur J Microbiol v. Jundishapur J Microbiol. Published online Feb Author information Article notes Copyright and License information Disclaimer.

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4. This article has been cited by other articles in PMC. Abstract Background: Poly 3-Hydroxybutyrate PHB , a class of Poly Hydroxyalkanoates PHAs , is a group of bacterial storage polymers, produced by various microorganisms in response to nutrient limitation.

Objectives: Our aim was PHB production from recombinant bacteria. Results: The extracted recombinant plasmid was digested with restriction enzymes. Conclusions: Various metabolic and fermentation methods have been used in some bacterial strains for PHB production. Background Petrochemical plastics have been developed into a major industry and are resistant to natural and chemical breakdowns 1.

Objectives Our objective was cloning and expression of the phb operon of R. Materials and Methods 3. Poly 3-Hydroxybutyrate Staining A thin bacterial smear was made on the clean glass slide. Results In R. Open in a separate window. Figure 1. Figure 2. Digestion of the Extracted Plasmid. Figure 3. Discussion PHAs are biodegradable polymers which could be a good substitute for current petrochemical plastics.

References 1. Sudesh K, Iwata T. Sustainability of biobased and biodegradable plastics. Clean Weinh. Bacterially produced polyhydroxyalkanoate PHA : converting renewable resources into bioplastics. Byrom D. A review of biodegradable polymers: uses, current developments in the synthesis and characterization of biodegradable polyesters, blends of biodegradable polymers and recent advances in biodegradation studies.

Polym Int. Nishida H, Tokiwa Y. Effects of heat treatment on microbial degradation. J Appl Polym Sci. Development of a process for the biotechnological large-scale production of 4-hydroxyvalerate-containing polyesters and characterization of their physical and mechanical properties. Metabolic engineering of poly 3-hydroxyalkanoates : from DNA to plastic.

Microbiol Mol Biol Rev. Fidler S, Dennis D. Polyhydroxyalkanoate production in recombinant Escherichia coli. Cordi et al. The optimum pH for L1 isozyme of laccase was 4. Han et al. Laccase extracted from Stereum ostrea showed the highest activity at pH 6. When fungi are grown in the medium of pH 5. Agitation is another factor which affects laccase production. Hess et al. Tavares et al. Laccase production has been seen to be highly dependent on fungus cultivation [ 61 ].

During secondary metabolic phase, ligninolytic systems are activated and triggered by nitrogen concentration [ 49 ]. Laccases are generally produced in low concentrations by laccase-producing fungi [ 39 ], but higher concentrations were obtained with the addition of various supplements such as xenobiotic compound to media [ 62 , 63 ]. The addition of aromatic compounds such as 2,5-xylidine, lignin, and veratryl alcohol is known to increase and induce laccase activity [ 63 , 64 ].

Veratryl alcohol is an aromatic compound; its addition to cultivation media results in an increase of laccase production [ 65 ]. At higher concentrations the 2,5-xylidine had a reducing effect due to toxicity [ 17 ]. The promoter region encoding for laccase contains various recognition sites that are specific for xenobiotics and heavy metals [ 66 ]; they bind to the recognition sites and induce laccase production.

The addition of inducer increases the concentration of a specific laccase enzyme [ 67 ]. Lee et al. This is a very economical way to enhance laccase production. Cellobiose increase laccase activity by profusing branch in certain Trametes species [ 68 ].

A new basidiomycete, Trametes sp. Submerged and solid-state modes of fermentation are used intensely for the production of laccase. Wild-type filamentous fungi are used for large-scale production of laccase in different cultivation techniques. Submerged fermentation involves the nurturing of microorganisms in high oxygen concentrated liquid nutrient medium. Viscosity of broth is the major problem associated with the fungal submerged fermentations.

When fungal cell grows, mycelium is formed which hinders impeller action, due to this limitation occuring in oxygen and mass transfer. For dealing with this problem, different strategies have been employed.

Bioreactor operates in continuous manner for obtaining high efficiency. In this Trametes versicolour is employed which decolorizes the synthetic dye, and for this purpose pulsed system has been developed [ 73 — 77 ]. Broth viscosity, oxygen, and mass transfer problems are also solved by cell immobilization.

Luke and Burton [ 78 ] reported that continuous laccase production takes place without enzyme deactivation for a period of 4 months due to the immobilization of the Neurospora crassa on membrane. For bioremediation of pentachlorophenol PCP and 2,4-dichlorophenol 2,4 DCP , nylon mesh is used for comparing the free cell culture of T.

Couto et al. The most effective way of producing laccase is Fed-batch operation through which the highest laccase activity can be obtained. SSF is suitable for the production of enzymes by using natural substrates such as agricultural residues because they mimic the conditions under which the fungi grow naturally [ 82 — 85 ]. The lignin, cellulose and hemicelluloses are rich in sugar and promote fungal growth in fermentor and make the process more economical [ 86 ].

The major drawback is the bioreactor design in which heat and mass transfer is limited. Different bioreactor configurations have been studied for laccase production such as immersion configuration, expanded bed, tray, inert nylon and noninert support barley bran in which tray configuration gave the best response [ 87 ]. A tray and immersion configuration is compared for laccase production by using grape seeds and orange peel as substrate [ 88 , 89 ].

Laccase production by both solid-state and submerged fermentation is higher in case of rice bran than other substrates. The rice bran inductive capability is based on the phenolic compounds such as ferulic acid, and vanillic acid which induce the laccase production [ 90 ]. Many agricultural wastes such as grape seeds, grape stalks, barley bran [ 91 ], cotton stalk, molasses waste water [ 92 ] and wheat bran [ 93 ] are also used as substrate for laccase production.

However, laccase production in both solid-state and submerged fermentation did not reach up to the maximum level; that is why prolonged cultivation is required. Ammonium sulphate is being commonly used for the enzyme purification for many years.

Laccase from LLP13 was first purified with column chromatography and then purified with gel filtration [ 10 , 11 ]. Laccase from T. Laccase from Stereum ostrea is purified with ammonium sulphate followed by Sephadex G column chromatography with fold purification [ 9 ]. Laccase is important because it oxidizes both the toxic and nontoxic substrates.

It is utilized in textile industry, food processing industry, wood processing industry, pharmaceutical industry, and chemical industry. This enzyme is very specific, ecologically sustainable and a proficient catalyst. Applications of laccase are as follows. Textile industry utilizes large volume of water and chemicals for wet processing. These chemicals range from inorganic compounds to organic compounds.

The chemical structure of dyes provides a resistance to fading when exposed to light, water, and other chemicals. Laccase degrades dye; that is why laccase-based processes have been developed which include synthetic dyes and are being used in the industry nowadays [ 96 , 97 ].

They concluded that T. They found that after decolourization, toxicity of few dyes remained the same while some became nontoxic [ 99 ]. Laccase-based hair dyes are less irritant and easier to handle than conventional hair dyes because laccases replace H 2 O 2 in the dye formulation [ ].

Laccase are also used in dechlorination process. Xylidine is a laccase inducer which increases dechlorination activity due to which dissolved oxygen concentration is reduced [ ]. Romero et al. Due to rapid industrialization and extensive use of pesticides for better agricultural productivity, contamination of soil, water, and air take place which is a serious environmental problem of today.

Polychlorinated biphenyls PCB , benzene, toluene, ethyl benzene, xylene BTEX , polycyclic aromatic hydrocarbons PAH , pentachlorophenol PCP , 1,1,1-trichloro-2,2-bis 4-chlorophenyl ethane DDT , and trinitrotoluene TNT are the substances which are known for their carcinogenic as well as mutagenic effect and are persistent in the environment. Keum and Li [ ] obtained laccase from T. Laccase obtained from T. Chlorine and oxygen-based chemical oxidants are used for the separation and degradation of lignin which is required for the preparation of paper at industrial level.

But some problems such as recycling, cost, and toxicity remain unsolved. However, in the existing bleaching process, LMS could be easily implemented because it leads to a partial replacement of ClO 2 in pulp mills [ 54 ]. In food industry, laccase is used for the elimination of undesirable phenolic compound in baking, juice processing, wine stabilization, and bioremediation of waste water [ 2 ].

Laccase improves not only the functionality but also the sensory properties [ ]. In beer industry, laccase not only provides stability but also increases the shelf life of beer. In beer, haze formation takes place which is stimulated by the naturally present proanthocyanidins polyphenol and is referred to as chill haze. At room temperature or above, warming of beer can redissolve the complex.

After certain periods of time, phenolic rings are replaced by the sulphydryl group and permanent haze is formed which cannot be redissolved. For polyphenol oxidation, laccase has been used which is capable of removing the excess oxygen and also due to which the shelf life of beer increases [ , ].

For making a fruit juice stable, laccase is commonly used. Phenol compounds and their oxidative products present naturally in the fruit juice give colour and taste to the juice. Colour and aroma change when polymerization and oxidation of phenolic and polyphenol take place. These changes are due to the high concentration of polyphenol and referred to as enzymatic darkening [ ]. Laccase treatment removes phenol as well as substrate-enzyme complex by the help of membrane filtration, and colour stability is achieved, although turbidity is present.

Laccase treatment is more effective in comparison to conventional methods. For improving the texture, volume, flavor and freshness of bread, wide range of enzymes are used. When laccase is added to the dough, strength of gluten structures in dough and baked products is improved: product volume increases, crumb structure improves, and softness of baked products takes place.

Due to the laccase addition, stickiness decreases, strength and stability increase and the ability of machine is also improved which can also seen by using a low-quality flour [ ]. At crushing and pressing stage, the high concentration of phenolic and polyphenolic compound play an important role in the wine production.

The high concentration of polyphenol obtained from the stems, seeds and skins which depends on the grape variety and vinification conditions contributes to of colour and astringency [ ]. Due to the complex event, polyphenol oxidation occurs in musts and wines resulting in the increase in colour and flavour change which is referred to as maderization [ ]. Catalytic factors, polyphenol removal, clarification, polyvinylpolypyrrolidone PVPP , and high doses of sulfur dioxide are utilized to prevent maderization.

Minussi et al. Laccase not only is used in food industry, paper and pulp industry, textile industry but also has other applications. In traditional system, PVPP is used for the removal of excess polyphenol which has low biodegradability and creates problems in wastewater treatment [ ]. Laccase has the ability to decrease odour arising from the garbage disposal sites, livestock farms and pulp mills.

Since laccases catalyze the electron transfer reactions without additional cofactors, they can also be used as biosensors to detect various phenolic compounds, oxygen, and azide. As biosensor, laccase can detect morphine, codeine, catecholamine, estimate phenol or other enzymes in fruit juice and plant flavonoid. Recently, laccase has been used as a biocatalyst for the synthesis of organic substance as well as in the design of biofuel cell [ 54 ].

For the bioremediation of food industry wastewater, laccase has been utilized. In bioremediation process, contaminants are biotransformed to their original status which has no bad effects on the environment [ ]. Large amount of polyphenol is present in the beer factory wastewater which is dark brown in colour and degraded by the white-rot fungus Coriolopsis gallica [ ]. Laccase produced from Trametes sp.

Olive mill wastewater is bioremediated by the help of immobilized laccase which is beneficial for the cultivation of fungi for laccase production [ ]. Many countries pose some rules and regulation for the pollutants which includes phenols and amines [ ]. Laccase has been found in the cuticles of many insect species [ , ] and is involved in cuticle sclerotization [ , ].

Laccases oxidizes catechols in the cuticle to their corresponding quinones, which catalyzes protein cross-linking reactions. In several holometabolous insects, laccase has been identified as the principal enzyme associated with cuticular hardening [ — ]. The insect laccase is a long amino-terminal sequence characterized by a unique domain consisting of several conserved cysteine, aromatic, and charged residues. In recent years, cloning of insect laccase genes has been performed [ , , ] and two main forms have been found: laccase-1 and laccase-2 [ , , , ].

Laccase-1 was found to be expressed in the midgut, Malpighian tubules [ , , ] and fat body as well as the epidermis of the tobacco hornworm, Manduca sexta , and may oxidize toxic compounds ingested by the insect [ ]. On the other hand, laccase-2 was involved in cuticle tanning of the red flour beetle, Tribolium castaneum [ ]. Recently, a laccase in the salivary glands of N. A possible function of salivary laccase diphenoloxidase is in the enhancement of the oxidative gelling occurring in the stylet sheath by a quinone-tanning reaction [ ] and rapid oxidization of potentially toxic monolignols to nontoxic polymers during feeding [ ].

When enzyme is immobilized, it becomes more vigorous and resistant to alteration in environment which allows easy recovery and reuse of enzyme for multiple purposes. That is why researchers are moving towards the efficient methods of immobilization which influence the properties of the biocatalyst.

Laccase immobilization has been studied with a wide range of different immobilization methods and substrates. Laccase produced by Trametes versicolour is immobilized on silica which is chemically modified with imidazole groups and Amberlite IRA Laccase can be immobilized on different pyrolytic graphite best support , ceramics supports and on a carbon fiber electrode where it acts as biosensor.

At the 12th day, maximum laccase activity 40, An optical biosensor is fabricated by using stacked films for the detection of phenolic compounds; 3-methylbenzothiazolinone hydrazone MBTH was immobilized on a silicate film and laccase on a chitosan film [ ]. Laccases are the versatile enzymes which catalyze oxidation reactions coupled to four-electron reduction of molecular oxygen to water. They are multicopper enzymes which are widely distributed in higher plants and fungi.

They are capable of degrading lignin and are present abundantly in many white-rot fungi. They decolorize and detoxify the industrial effluents and help in wastewater treatment. They act on both phenolic and nonphenolic lignin-related compounds as well as highly recalcitrant environmental pollutants which help researchers to put them in various biotechnological applications. They can be effectively used in paper and pulp industries, textile industries, xenobiotic degradation, and bioremediation and act as biosensor.

Laccase has been applied to nanobiotechnology which is an increasing research field and catalyzes electron transfer reactions without additional cofactors. Recently several techniques have been developed for the immobilization of biomolecule such as micropatterning, self-assembled monolayer, and layer-by-layer technique which immobilize laccase and preserve their enzymatic activity.

Hence laccase is receiving much attention of researchers around the globe. This paper shows that laccase has a great potential application in several areas of food industry. However, one of the limitations for the large-scale application of laccase is the lack of capacity to produce large volumes of highly active enzyme at an affordable cost. The use of inexpensive sources for laccase production is being explored in recent times. In this regard, an emerging field in management of industrial wastewater is exploiting its nutritive potential for production of laccase.

Besides solid wastes, wastewater from the food processing industry is particularly promising for that. R, Mangalayatan University Aligarh, India for providing necessary facilities and encouragement. They are also thankful to all faculty members of the Institute of Biomedical Education and Research, Mangalayatan University Aligarh, India for their generous help and suggestions during the paper preparation. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Special Issues. Academic Editor: Alane Beatriz Vermelho. Received 25 Jan Revised 30 Mar Accepted 16 Apr Published 21 Jun Abstract Laccase belongs to the blue multicopper oxidases and participates in cross-linking of monomers, degradation of polymers, and ring cleavage of aromatic compounds.

Introduction In the recent years, enzymes have gained great importance in Industries; laccases are one among them which are widely present in the nature. Sources of Laccases Laccase is generally found in higher plants and fungi but recently it was found in some bacteria such as S. Mechanism of Laccases The laccase catalysis occurs due to the reduction of one oxygen molecule to water accompanied with the oxidation of one electron with a wide range of aromatic compounds which includes polyphenol [ 21 ], methoxy-substituted monophenols, and aromatic amines [ 14 ].

Properties of Laccase Enzyme Laccases are mainly monomeric, dimeric, and tetrameric glycoprotein. Production of Laccase Laccases are the enzymes which are secreted out in the medium extracellularey by several fungi [ 25 ] during the secondary metabolism but not all fungal species produce laccase such as Zygomycetes and Chytridiomycetes [ 26 ]. Influence of Carbon and Nitrogen Source The organism grown in the defined medium contains 0.

Influence of Temperature The effect of temperature is limited in case of laccase production. Influence of pH The effect of pH is limited in case of laccase production [ 19 ]. Influence of Agitator Agitation is another factor which affects laccase production.

Influence of Inducer Laccase production has been seen to be highly dependent on fungus cultivation [ 61 ]. Type of Cultivation Submerged and solid-state modes of fermentation are used intensely for the production of laccase. Submerged Fermentation Submerged fermentation involves the nurturing of microorganisms in high oxygen concentrated liquid nutrient medium. Solid-State Fermentation SSF is suitable for the production of enzymes by using natural substrates such as agricultural residues because they mimic the conditions under which the fungi grow naturally [ 82 — 85 ].

Purification of Laccase Ammonium sulphate is being commonly used for the enzyme purification for many years. Applications of Laccase Laccase is important because it oxidizes both the toxic and nontoxic substrates. Dye Decolorization Textile industry utilizes large volume of water and chemicals for wet processing. Bioremediation and Biodegradation Due to rapid industrialization and extensive use of pesticides for better agricultural productivity, contamination of soil, water, and air take place which is a serious environmental problem of today.

Paper and Pulp Industry Chlorine and oxygen-based chemical oxidants are used for the separation and degradation of lignin which is required for the preparation of paper at industrial level. Food Processing Industry In food industry, laccase is used for the elimination of undesirable phenolic compound in baking, juice processing, wine stabilization, and bioremediation of waste water [ 2 ].

Other Applications Laccase not only is used in food industry, paper and pulp industry, textile industry but also has other applications. Laccase Function in Insects Laccase has been found in the cuticles of many insect species [ , ] and is involved in cuticle sclerotization [ , ]. Laccase Immobilization When enzyme is immobilized, it becomes more vigorous and resistant to alteration in environment which allows easy recovery and reuse of enzyme for multiple purposes.

Conclusion Laccases are the versatile enzymes which catalyze oxidation reactions coupled to four-electron reduction of molecular oxygen to water. Future Trends and Perspectives This paper shows that laccase has a great potential application in several areas of food industry. References P. View at: Google Scholar S. Couto and J. Gianfreda, F. Xu, and J. View at: Google Scholar J. Faccelo and O.

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Much of this polymer production is composed of plastic materials that are generally non-biodegradable. This widespread use of plastics raises a significant threat to the environment due to the lack of proper waste management and a until recently cavalier community behavior to maintain proper control of this waste stream.

Response to these conditions has elicited an effort to devise innovative strategies for plastic waste management, invention of biodegradable polymers, and education to promote proper disposal. Technologies available for current polymer degradation strategies are chemical, thermal, photo, and biological techniques [ 2 , 3 , 4 , 5 , 6 ]. The physical properties displayed in Table 1 show little differences in density but remarkable differences in crystallinity and lifespan.

Crystallinity has been shown to play a very directing role in certain biodegradation processes on select polymers. Selected features of major commercial thermoplastic polymers [ 7 ]. Polymers are generally carbon-based commercialized polymeric materials that have been found to have desirable physical and chemical properties in a wide range of applications.

A recent assessment attests to the broad range of commercial materials that entered to global economy since as plastics. The mass production of virgin polymers has been assessed to be million metric tons for the period of through [ 8 ]. Packaging plastics are recycled in remarkably low quantities.

Should current production and waste management trends continue, landfill plastic waste and that in the natural environment could exceed 12, Mt of plastic waste by [ 9 ]. A polymer is easily recognized as a valuable chemical made of many repeating units [ 10 ]. Polymers can be chemically synthesized in a variety of ways depending on the chemical characteristics of the monomers thus forming a desired product.

Nature affords many examples of polymers which can be used directly or transformed to form materials required by society serving specific needs. The polymers of concern are generally composed of carbon and hydrogen with extension to oxygen, nitrogen and chlorine functionalities see Figure 1 for examples. Chemical resistance, thermal and electrical insulation, strong and light-weight, and myriad applications where no alternative exists are polymer characteristics that continue to make polymers attractive.

Significant polymer application can be found in the automotive, building and construction, and packaging industries [ 12 ]. Structures of major commercial thermoplastic polymers [ 11 ]. The environmental behavior of polymers can be only discerned through an understanding of the interaction between polymers and environment under ambient conditions.

This interaction can be observed from surface properties changes that lead to new chemical functionality formation in the polymer matrix. New functional groups contribute to continued deterioration of the polymeric structure in conditions such as weathering. Discoloration and mechanical stiffness of the polymeric mass are often hallmarks of the degradative cycle in which heat, mechanical energy, radiation, and ozone are contributing factors [ 13 ].

Polyolefins PO are the front-runners of the global industrial polymer market where a broad range of commercial products contribute to our daily lives in the form o packaging, bottles, automobile parts and piping. The sources of these polymers are low-cost petrochemicals and natural gas with monomers production dependent on cracking or refining of petroleum.

This class of polymers has a unique advantage derived from their basic composition of carbon and hydrogen in contrast to other available polymers such as polyurethanes, poly vinyl chloride and polyamides [ 14 ]. This continuous increase suggests that as material use broadens yearly, the amount of waste will also increase and present waste disposal problems. Polyolefin biological and chemical inertness continues to be recognized as an advantage.

However, this remarkable stability found at many environmental conditions and the degradation resistance leads to environmental accumulation and an obvious increase to visible pollution and ancillary contributing problems. Desired environmental properties impact the polyolefin market on the production side as well as product recyclability [ 15 ]. Biodegradation utilizes the functions of microbial species to convert organic substrates polymers to small molecular weight fragments that can be further degraded to carbon dioxide and water [ 16 , 17 , 18 , 19 , 20 , 21 ].

The physical and chemical properties of a polymer are important to biodegradation. Biodegradation efficiency achieved by the microorganisms is directly related to the key properties such as molecular weight and crystallinity of the polymers. Enzymes engaged in polymer degradation initially are outside the cell and are referred to as exo-enzymes having a wide reactivity ranging from oxidative to hydrolytic functionality.

Their action on the polymer can be generally described as depolymerization. The exo-enzymes generally degrade complex polymer structure to smaller, simple units that can take in the microbial cell to complete the process of degradation. Polymer degradation proceeds to form new products during the degradation path leading to mineralization which results in the formation of process end-products such as, e.

Oxygen is the required terminal electron acceptor for the aerobic degradation process. Aerobic conditions lead to the formation of CO 2 and H 2 O in addition to the cellular biomass of microorganisms during the degradation of the plastic forms. Where sulfidogenic conditions are found, polymer biodegradation leads to the formation of CO 2 and H 2 O. Contrasting aerobic degradation with anaerobic conditions, the aerobic process is found to be more efficient.

As solid materials, plastics encounter the effects of biodegradation at the exposed surface. In the unweathered polymeric structure, the surface is affected by biodegradation whereas the inner part is generally unavailable to the effects of biodegradation. Weathering may mechanically affect the structural integrity of the plastic to permit intrusion of bacteria or fungal hyphae to initiate biodegradation at inner loci of the plastic. The rate of biodegradation is functionally dependent on the surface area of the plastic.

As the microbial-colonized surface area increases, a faster biodegradation rate will be observed assuming all other environmental conditions to be equal [ 24 ]. Microorganisms can break organic chemicals into simpler chemical forms through biochemical transformation. Polymer biodegradation is a process in which any change in the polymer structure occurs as a result of polymer properties alteration resulting from the transformative action of microbial enzymes, molecular weight reduction, and changes to mechanical strength and surface properties attributable to microbial action.

The biodegradation reaction for a carbon-based polymer under aerobic conditions can be formulated as follows:. Assimilation of the carbon comprising the polymer C polymer by microorganisms results in conversion to CO 2 and H 2 O with production of more microbial biomass C biomass. In turn, C biomass is mineralized across time by the microbial community or held in reserve as storage polymers [ 25 ]. The following set of equations is a more complete description of the aerobic plastic biodegradation process:.

The conversion to CO 2 is referred to as microbial mineralization. Each oligomeric fragment is expected to proceed through of sequential steps in which the chemical and physical properties are altered leading to the desired benign result.

A technology for monitoring aerobic biodegradation has been developed and optimized for small organic pollutants using oxygen respirometry where the pollutant degrades at a sufficiently rapid rate for respirometry to provide expected rates of biodegradation. When polymers are considered, a variety of analytical approaches relating to physical and chemical changes are employed such as differential scanning calorimetry, scanning electron microscopy, thermal gravimetric analysis, Fourier transform infrared spectrometry, gas chromatograph-mass spectrometry, and atomic force microscopy [ 26 ].

Since most polymer disposal occurs in our oxygen atmosphere, it is important to recognize that aerobic biodegradation will be our focus but environmental anaerobic conditions do exist that may be useful to polymer degradation. The distinction between aerobic and anaerobic degradation is quite important since it has been observed that anaerobic conditions support slower biodegradation kinetics.

Anaerobic biodegradation can occur in the environment in a variety of situations. Burial of polymeric materials initiates a complex series of chemical and biological reactions. Oxygen entrained in the buried materials is initially depleted by aerobic bacteria. The following oxygen depleted conditions provide conditions for the initiation of anaerobic biodegradation.

The buried strata are generally covered by 3-m-thick layers which prevent oxygen replenishment. The alternate electron acceptors such as nitrate, sulfate, or methanogenic conditions enable the initiation of anaerobic biodegradation. Any introduction of oxygen will halt an established anaerobic degradation process. This formulation for the aerobic biodegradation of polymers can be improved due to the complexity of the processes involved in polymer biodegradation [ 27 ].

Biodegradation, defined as a decomposition of substances by the action of microorganisms, leading to mineralization and the formation of new biomass is not conveniently summarized. A new analysis is necessary to assist the formulation of comparative protocols to estimate biodegradability. In this context, polymer biodegradation is defined as a complex process composed of the stages of biodeterioration, biofragmentation, and assimilation [ 28 ].

The biological activity inferred in the term biodegradation is predominantly composed of, biological effects but within nature biotic and abiotic features act synergistically in the organic matter degradation process. Degradation modifying mechanical, physical and chemical properties of a material is generally referred to as deterioration.

Abiotic and biotic effects combine to exert changes to these properties. This biological action occurs from the growth of microorganisms on the polymer surface or inside polymer material. Mechanical, chemical, and enzymatic means are exerted by microorganisms, thereby modifying the gross polymer material properties. Environmental conditions such as atmospheric pollutants, humidity, and weather strongly contribute to the overall process. The adsorbed pollutants can assist the material colonization by microbial species.

A diverse collection of bacteria, protozoa, algae, and fungi are expected participants involved in biodeterioration. The development of different biota can increase biodeterioration by facilitating the production of simple molecules. Fragmentation is a material breaking phenomenon required to meet the constraints for the subsequent event called assimilation. Polymeric material has a high molecular weight which is restricted by its size in its transit across the cell wall or cytoplasmic membrane.

Reduction of polymeric molecule size is indispensable to this process. Changes to molecular size can occur through the involvement of abiotic and biotic processes which are expected to reduce molecular weight and size. The utility of enzymes derived from the microbial biomass could provide the required molecular weight reductions. Assimilation describes the integration of atoms from fragments of polymeric materials inside microbial cells.

The microorganisms benefit from the input of energy, electrons and elements i. Assimilated substrates are expected to be derived from biodeterioration and biofragmentation effects. Non-assimilated materials, impermeable to cellular membranes, are subject to biotransformation reactions yielding products that may be assimilated.

Molecules transported across the cell membrane can be oxidized through catabolic pathways for energy storage and structural cell elements. Assimilation supports microbial growth and reproduction as nutrient substrates e. The polymer substrate properties are highly important to any colonization of the surface by either bacteria or fungi [ 29 ]. The topology of the surface may also be important to the colonization process. The polymer properties of molecular weight, shape, size and additives are each unique features which can limit biodegradability.

The molecular weight of a polymer can be very limiting since the microbial colonization depends on surface features that enable the microorganisms to establish a locus from which to expand growth. Polymer crystallinity can play a strong role since it has been observed that microbial attachment to the polymer surface occurs and utilizes polymer material in amorphous sections of the polymer surface.

Polymer additives are generally low molecular weight organic chemicals that can provide a starting point for microbial colonization due to their ease of biodegradation Figure 2. Factors controlling polymer biodegradation [ 30 ]. Weather is responsible for the deterioration of most exposed materials. Abiotic contributors to these conditions are moisture in its variety of forms, non-ionizing radiation, and atmospheric temperature.

When combined with wind effects, pollution, and atmospheric gases, the overall process of deterioration can be quite formable. The ultraviolet UV component of the solar spectrum contributes ionizing radiation which plays a significant role in initiating weathering effects. Visible and near-infrared radiation can also contribute to the weathering process. Other factors couple with solar radiation synergistically to significantly influence the weathering processes. The quality and quantity of solar radiation, geographic location changes, time of day and year, and climatological conditions contribute to the overall effects.

Effects of ozone and atmospheric pollutants are also important since each can interact with atmospheric radiation to result in mechanical stress such as stiffening and cracking. Moisture when combined with temperature effects can assist microbial colonization. The biotic contributors can strongly assist the colonization by providing the necessary nutrients for microbial growth. Hydrophilic surfaces may provide a more suitable place for colonization to ensue. Readily available exoenzymes from the colonized area can initiate the degradation process.

Communities of microorganisms attached to a surface are referred to as biofilms [ 31 ]. The microorganisms forming a biofilm undergo remarkable changes during the transition from planktonic free-swimming biota to components of a complex, surface-attached community Figure 3.

The process is quite simple with planktonic microorganism encountering a surface where some adsorb followed by surface release to final attachment by the secretion of exopolysaccharides which act as an adhesive for the growing biofilm [ 33 ]. New phenotypic characteristics are exhibited by the bacteria of a biofilm in response to environmental signals. Initial cell-polymer surface interactions, biofilm maturation, and the return to planktonic mode of growth have regulatory circuits and genetic elements controlling these diverse functions.

Studies have been conducted to explore the genetic basis of biofilm development with the development of new insights. Compositionally, these films have been found to be a single microbial species or multiple microbial species with attachment to a range of biotic and abiotic surfaces [ 34 , 35 ]. Mixed-species biofilms are generally encountered in most environments. Under the proper nutrient and carbon substrate supply, biofilms can grow to massive sizes.

With growth, the biofilm can achieve large film structures that may be sensitive to physical forces such as agitation. Under such energy regimes, the biofilm can detach. An example of biofilm attachment and utility can be found in the waste water treatment sector where large polypropylene disks are rotated through industrial or agriculture waste water and then exposed to the atmosphere to treat pollutants through the intermediacy of cultured biofilms attached to the rotating polypropylene disk.

Microbial attachment processes to a polymer surface [ 32 ]. Biofilm formation and activity to polymer biodegradation are complex and dynamic [ 36 ]. The physical attachment offers a unique scenario for the attached microorganism and its participation in the biodegradation. After attachment as a biofilm component, individual microorganisms can excrete exoenzymes which can provide a range of functions. Due to the mixed-species composition found in most environments, a broad spectrum of enzymatic activity is generally possible with wide functionalities.

Biofilm formation can be assisted by the presence of pollutant chemical available at the polymer surface. The converse is also possible where surfaces contaminated with certain chemicals can prohibit biofilm formation. Biofilms continue to grow with the input of fresh nutrients, but when nutrients are deprived, the films will detach from the surface and return to a planktonic mode of growth.

Overall hydrophobicity of the polymer surface and the surface charge of a bacterium may provide a reasonable prediction of surfaces to which a microorganism might colonize [ 37 ]. These initial cell-surface and cell-cell interactions are very useful to biofilm formation but incomplete Figure 4.

Microbial surfaces are heterogeneous, and can change widely in response to environmental changes. Five stages of biofilm development: have been identified as 1 initial attachment, 2 irreversible attachment, 3 maturation I, 4 maturation II, and 5 dispersion. Further research is required to provide the understanding of microbial components involved in biofilm development and regulation of their production to assemble to various facets of this complex microbial phenomenon [ 38 ].

Biofilm formation and processes [ 34 ]. The activities envisioned in this scenario depicted in Figure 4 are the reversible adsorption of bacteria occurring at the later time scale, irreversible attachment of bacteria occurring at the second-minute time scale, growth and division of bacteria in hours-days, exopolymer production and biofilm formation in hours-days, and attachment and other organisms to biofilm in days-months.

The evaluation of the extent of polymer biodegradation is made difficult by the dependence on polymer surface and the departure of degradation kinetics from the techniques available for small pollutant molecule techniques [ 39 ]. For applications for polymer biodegradation a variety of techniques have been applied.

The testing regime must be explicitly described within a protocol of steps that can be collected for various polymers and compared on an equal basis. National and international efforts have developed such protocols to enable the desired comparisons using rigorous data collecting techniques and interpretation [ 40 ].

Each of these polymers is subject to very slow fragmentation to form small particles in a process expected to require centuries of exposure to photo-, physical, and biological degradation processes. Until recently, the commercial polymers were not expected to biodegrade. The current perspective supports polymer biodegradation with hopeful expectation that these newly encountered biodegradation processes can be transformed into technologies capable of providing major assistance to the ongoing task of waste polymer management.

The polyolefins such as polyethylene PE have been recognized as a polymer remarkably resistant to degradation [ 42 ]. Products made with PE are very diverse and a testament to its chemical and biological inertness. The biodegradation of the polyolefins is complex and incompletely understood.

Pure strains elicited from the environment have been used to investigate metabolic pathways or to gain a better understanding of the effect that environmental conditions have on polyolefin degradation. This strategy ignores the importance of different microbial species that could participate in a cooperative process. Treatment of the complex environments associated with polymeric solid waste could be difficult with information based on pure strain analysis. Mixed and complex microbial communities have been used and encountered in different bioremediation environments [ 43 ].

Antibiotic resistance can develop rapidly through changes in the expression of efflux pumps, including changes to some antibiotics considered to be drugs of last resort. It is therefore imperative that new antibiotics, resistance-modifying agents and, more specifically, efflux pump inhibitors EPIs are characterized.

The use of bacterial resistance modifiers such as EPIs could facilitate the re-introduction of therapeutically ineffective antibiotics back into clinical use such as ciprofloxacin and might even suppress the emergence of MDR strains. Here we review the literature on bacterial EPIs derived from natural sources, primarily those from plants. The resistance-modifying activities of many new chemical classes of EPIs warrant further studies to assess their potential as leads for clinical development.

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Abiotic contributors to these conditions are moisture in its variety of forms, non-ionizing radiation, and atmospheric temperature. When combined with wind effects, pollution, and atmospheric gases, the overall process of deterioration can be quite formable.

The ultraviolet UV component of the solar spectrum contributes ionizing radiation which plays a significant role in initiating weathering effects. Visible and near-infrared radiation can also contribute to the weathering process. Other factors couple with solar radiation synergistically to significantly influence the weathering processes.

The quality and quantity of solar radiation, geographic location changes, time of day and year, and climatological conditions contribute to the overall effects. Effects of ozone and atmospheric pollutants are also important since each can interact with atmospheric radiation to result in mechanical stress such as stiffening and cracking. Moisture when combined with temperature effects can assist microbial colonization. The biotic contributors can strongly assist the colonization by providing the necessary nutrients for microbial growth.

Hydrophilic surfaces may provide a more suitable place for colonization to ensue. Readily available exoenzymes from the colonized area can initiate the degradation process. Communities of microorganisms attached to a surface are referred to as biofilms [ 31 ]. The microorganisms forming a biofilm undergo remarkable changes during the transition from planktonic free-swimming biota to components of a complex, surface-attached community Figure 3. The process is quite simple with planktonic microorganism encountering a surface where some adsorb followed by surface release to final attachment by the secretion of exopolysaccharides which act as an adhesive for the growing biofilm [ 33 ].

New phenotypic characteristics are exhibited by the bacteria of a biofilm in response to environmental signals. Initial cell-polymer surface interactions, biofilm maturation, and the return to planktonic mode of growth have regulatory circuits and genetic elements controlling these diverse functions. Studies have been conducted to explore the genetic basis of biofilm development with the development of new insights.

Compositionally, these films have been found to be a single microbial species or multiple microbial species with attachment to a range of biotic and abiotic surfaces [ 34 , 35 ]. Mixed-species biofilms are generally encountered in most environments. Under the proper nutrient and carbon substrate supply, biofilms can grow to massive sizes. With growth, the biofilm can achieve large film structures that may be sensitive to physical forces such as agitation.

Under such energy regimes, the biofilm can detach. An example of biofilm attachment and utility can be found in the waste water treatment sector where large polypropylene disks are rotated through industrial or agriculture waste water and then exposed to the atmosphere to treat pollutants through the intermediacy of cultured biofilms attached to the rotating polypropylene disk. Microbial attachment processes to a polymer surface [ 32 ].

Biofilm formation and activity to polymer biodegradation are complex and dynamic [ 36 ]. The physical attachment offers a unique scenario for the attached microorganism and its participation in the biodegradation. After attachment as a biofilm component, individual microorganisms can excrete exoenzymes which can provide a range of functions. Due to the mixed-species composition found in most environments, a broad spectrum of enzymatic activity is generally possible with wide functionalities.

Biofilm formation can be assisted by the presence of pollutant chemical available at the polymer surface. The converse is also possible where surfaces contaminated with certain chemicals can prohibit biofilm formation. Biofilms continue to grow with the input of fresh nutrients, but when nutrients are deprived, the films will detach from the surface and return to a planktonic mode of growth.

Overall hydrophobicity of the polymer surface and the surface charge of a bacterium may provide a reasonable prediction of surfaces to which a microorganism might colonize [ 37 ]. These initial cell-surface and cell-cell interactions are very useful to biofilm formation but incomplete Figure 4.

Microbial surfaces are heterogeneous, and can change widely in response to environmental changes. Five stages of biofilm development: have been identified as 1 initial attachment, 2 irreversible attachment, 3 maturation I, 4 maturation II, and 5 dispersion. Further research is required to provide the understanding of microbial components involved in biofilm development and regulation of their production to assemble to various facets of this complex microbial phenomenon [ 38 ].

Biofilm formation and processes [ 34 ]. The activities envisioned in this scenario depicted in Figure 4 are the reversible adsorption of bacteria occurring at the later time scale, irreversible attachment of bacteria occurring at the second-minute time scale, growth and division of bacteria in hours-days, exopolymer production and biofilm formation in hours-days, and attachment and other organisms to biofilm in days-months.

The evaluation of the extent of polymer biodegradation is made difficult by the dependence on polymer surface and the departure of degradation kinetics from the techniques available for small pollutant molecule techniques [ 39 ]. For applications for polymer biodegradation a variety of techniques have been applied.

The testing regime must be explicitly described within a protocol of steps that can be collected for various polymers and compared on an equal basis. National and international efforts have developed such protocols to enable the desired comparisons using rigorous data collecting techniques and interpretation [ 40 ]. Each of these polymers is subject to very slow fragmentation to form small particles in a process expected to require centuries of exposure to photo-, physical, and biological degradation processes.

Until recently, the commercial polymers were not expected to biodegrade. The current perspective supports polymer biodegradation with hopeful expectation that these newly encountered biodegradation processes can be transformed into technologies capable of providing major assistance to the ongoing task of waste polymer management. The polyolefins such as polyethylene PE have been recognized as a polymer remarkably resistant to degradation [ 42 ].

Products made with PE are very diverse and a testament to its chemical and biological inertness. The biodegradation of the polyolefins is complex and incompletely understood. Pure strains elicited from the environment have been used to investigate metabolic pathways or to gain a better understanding of the effect that environmental conditions have on polyolefin degradation. This strategy ignores the importance of different microbial species that could participate in a cooperative process.

Treatment of the complex environments associated with polymeric solid waste could be difficult with information based on pure strain analysis. Mixed and complex microbial communities have been used and encountered in different bioremediation environments [ 43 ]. The type of polymer used as the substrate can strongly influence the microbial community structure colonizing PE surface. A significant number of microbial strains have been identified for the deterioration caused by their interaction with the polymer surface [ 44 ].

Microorganisms have been categorized for their involvement in PE colonization and biodegradation or the combination. Some research studies did not conduct all the tests required to verify PE biodegradation. A more inclusive approach to assessing community composition, including the non-culturable fraction of microorganisms invisible by traditional microbiology methods is required in future assessments. The diversity of microorganisms capable of degrading PE extends beyond 17 genera of bacteria and nine genera of fungi [ 45 ].

These numbers are expected to increase with the use of more sensitive isolation and characterization techniques using rDNA sequencing. Polymer additives can affect the kinds of microorganisms colonizing the surfaces of these polymers. The ability of microorganisms to colonize the PE surfaces exhibits a variety of effects on polymer properties.

Seven different characteristics have been identified and are used to monitor the extent of polymer surface change resulting from biodegradation of the polymer. The use of surfactants has become important to PE biodegradation. A combination of P. The metabolically diverse genus Pseudomonas has been investigated for its capabilities to degrade and metabolize synthetic plastics.

Pseudomonas species found in environmental matrices have been identified to degrade a variety of polymers including PE, and PP [ 47 ]. In an ancillary study, thermophilic consortia of Brevibacillus sps. The larval stage of two waxworm species, Galleria mellonella and Plodia interpunctella , has been observed to degrade LDPE without pretreatment [ 49 , 50 ].

The worms could macerate PE as thin film shopping bags and metabolize the film to ethylene glycol which in turn biodegrades rapidly. From the guts of Plodia interpunctella waxworms two strains of bacteria, Enterobacter asburiae YP1 and Bacillus sp. YP1, were isolated and found to degrade PE in laboratory conditions. The two strains of bacteria were shown to reduce the polymer film hydrophobicity during a day incubation. Changes to the film surface as cavities and pits were observed using scanning electron microscopy and atomic-force microscopy.

The waxworm research has been scrutinized and found to be lacking the necessary information to support the claims of the original Galleria mellonella report [ 51 ]. Polypropylene PP is very similar to PE, in solution behavior and electrical properties.

Mechanical properties and thermal resistance are improved with the addition of the methyl group but chemical resistance decreases. There are three forms of propylene selectively formed from the monomer isotactic, syndiotactic, and atactic due to the different geometric relationships achievable through polymerization technology. PP properties are strongly directed by tacticity or the methyl group orientation as related the methyl groups in neighboring monomer units.

Isotactic PP has a greater degree of crystallinity than atactic and syndiotactic PP and therefore more difficult to biodegrade. The high molar mass of PP prohibits permeation through the microbial cell membrane which thwarts metabolism by living organisms.

It is generally recognized that abiotic degradation provides a foothold for microorganisms to form a biofilm. With partial destruction of the polymer surface by abiotic effects the microbes can then start breaking the damaged polymer chains [ 52 ].

PS is a sturdy thermoplastic commonly used in short-lifetime items that contribute broadly to the mass of poorly controlled polymers [ 53 ]. PS has been thought to be non-biodegradable. The rate of biodegradation encountered in the environment is very slow leading to prolonged persistence as solid waste.

In the past, PS was recycled through mechanical, chemical, and thermal technologies yielding gaseous and liquid daughter products [ 54 ]. A rather large collection of studies has shown that PS is subject to biodegradation but at a very slow rate in the environment. A sheet of PS buried for 32 years.

The hydrophobicity of the polymer surface, a function of molecular structure and composition, detracts from the effectiveness of microbial attachment [ 56 , 57 ]. The general lack of water solubility of PS prohibits the transport into microbial cells for metabolism. A narrow range of microorganisms have been elicited for the environment and found to degrade PS [ 53 ]. Bacillus and Pseudomonas strains isolated from soil samples have been shown to degrade brominated high impact PS.

The activity was seen in weight loss and surface changes to the PS film. Soil invertebrates such as the larvae of the mealworm Tenebrio molitor Linnaeus have been shown to chew and eat Styrofoam [ 57 ]. Samples of the larvae were fed Styrofoam as the sole diet for 30 days and compared with worms fed a conventional diet. The worms feeding Styrofoam survived for 1 month after which they stopped eating as they entered the pupae stage and emerged as adults after a subsequent 2 weeks.

It appears that Styrofoam feeding did not lead to any lethality for the mealworms. The ingested PS mass was efficiently depolymerized within the larval gut during the retention time of 24 hours and converted to CO 2 [ 51 ]. This remarkable behavior by the mealworm can be considered the action of an efficient bioreactor. The mealworm can provide all the necessary components for PS treatment starting with chewing, ingesting, mixing, reacting with gut contents, and microbial degradation by gut microbial consortia.

A PS-degrading bacterial strain Exiguobacterium sp. Superworms Zophobas morio were found to exhibit similar activity toward Styrofoam. Brominated high impact polystyrene blend of polystyrene and polybutadiene has been found to be degraded by Pseudomonas and Bacillus strains [ 58 ]. In a complementary study, four non-pathogenic cultures Enterobacter sp. PVC is manufactured in two forms rigid and flexible. The rigid form can be found in the construction industry as pipe or in structural applications.

The soft and flexible form can be made through the incorporation of plasticizers such as phthalates. Credit cards, bottles, and non-food packaging are notable products with a PVC composition. PVC has been known from its inception as a polymer with remarkable resistance to degradation [ 60 ]. Thermal and photodegradation processes are widely recognized for their role in the weathering processes found with PVC [ 61 , 62 ].

The recalcitrant feature of polyvinyl chloride resistance to biodegradation becomes a matter of environmental concern across the all processes extending from manufacturing to waste disposal. Few reports are available relating the extent of PVC biodegradation. Early studies investigated the biodegradation of low-molecular weight PVC by white rot fungi [ 63 ].

Plasticized PVC was found to be degraded by fungi such as As. Modifying the PVC film composition with adjuvants such as cellulose and starch provided a substrate that fungi could also degrade [ 65 ]. Several investigations of soil bacteria for the ability to degrade PVC from enrichment cultures were conducted on different locations [ 66 ]. Mixed cultures containing bacteria and fungi were isolated and found to grow on plasticized PVC [ 67 ].

Significant differences were observed for the colonization by the various components of the mixed isolates during very long exposure times [ 68 ]. Significant drift in isolate activity was averted through the use of talc. Consortia composed of a combination of different bacterial strains of Pseudomonas otitidis , Bacillus cereus , and Acanthopleurobacter pedis have the ability to degrade PVC in the environment [ 64 ].

These results offer the opportunity to optimization conditions for consortia growth in PVC and use as a treatment technology to degrade large collections of PVC. PUR encompass a broad field of polymer synthesis where a di- or polyisocyanate is chemically linked through carbamate urethane formation. These thermosetting and thermoplastic polymers have been utilized to form microcellular foams, high performance adhesives, synthetic fibers, surface coatings, and automobile parts along with a myriad of other applications.

The carbamate linkage can be severed by chemical and biological processes [ 70 ]. Aromatic esters and the extent of the crystalline fraction of the polymer have been identified as important factors affecting the biodegradation of PUR [ 71 , 72 ]. Acid and base hydrolysis strategies can sever the carbamate bond of the polymer. Microbial ureases, esterases and proteases can enable the hydrolysis the carbamate and ester bonds of a PUR polymer [ 71 , 73 , 74 ]. Bacteria have been found to be good sources for enzymes capable of degrading PUR polymers [ 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ].

Fungi are also quite capable of degrading PUR polymers [ 83 , 84 , 85 ]. Each of the enzyme systems has their preferential targets: ureases attack the urea linkages [ 86 , 87 , 88 ] with esterases and proteases hydrolyzing the ester bonds of the polyester PUR as a major mechanism for its enzymatic depolymerization [ 89 , 90 , 91 , 92 ]. PUR polymers appear to be more amenable to enzymatic depolymerization or degradation but further searches and inquiry into hitherto unrecognized microbial PUR degrading activities is expected to offer significant PUR degrading activities.

PET is a polyester commonly marketed as a thermoplastic polymer resin finding use as synthetic fibers in clothing and carpeting, food and liquid containers, manufactured objects made through thermoforming, and engineering resins with glass fiber. Composed of terephthalic acid and ethylene glycol through the formation of ester bonds, PET has found a substantial role in packaging materials, beverage bottles and the textile industry.

In many of its commercial forms, PET is semicrystalline having crystalline and amorphous phases which has a major effect on PET biodegradability. The durability and the resulting low biodegradability of PET are due to the presence of repeating aromatic terephthalate units in its backbone and the corresponding limited mobility of the polymer chains [ 92 ].

The semicrystalline PET polymer also contains both amorphous and crystalline fractions with a strong effect on its biodegradability. At higher temperatures, the amorphous fraction of PET becomes more flexible and available to enzymatic degradation [ 95 , 96 ]. The hydrolysis of PET by enzymes has been identified as a surface erosion process [ 97 , 98 , 99 , ]. The hydrophobic surface significantly limits biodegradation due to the limited ability for microbial attachment.

The hydrophobic nature of PET poses a significant barrier to microbial colonization of the polymer surface thus attenuating effective adsorption and access by hydrolytic enzymes to accomplish the polymer degradation [ ]. A wide array of hydrolytic enzymes including hydrolases, lipases, esterases, and cutinases has been shown to have the ability to hydrolyze amorphous PET polymers and modify PET film surfaces.

Microbes from a vast collection of waste sites and dumping situations have been studied for their ability to degrade PET. A subunit of PET, diethylene glycol phthalate has been found to be a source of carbon and energy necessary to the sustenance of microbial life. Enzyme modification may be effectively employed to improve the efficiency and specificity of the polyester degrading enzymes acknowledged to be active degraders of PET [ ].

Significant efforts have been extended to developing an understanding of the enzymatic activity of high-performing candidate enzymes through selection processes, mechanistic probes, and enzyme engineering. In addition to hydrolytic enzymes already identified, enzymes found in thermophilic anaerobic sludge were found to degrade PET copolymers formed into beverage bottles [ ]. Recently, the discovery of microbial activity capable of complete degradation of widely used beverage bottle plastic expands the range of technology options available for PET treatment.

A microorganism isolated from the area adjacent to a plastic bottle-recycling facility was shown to aerobically degrade PET to small molecular daughter products and eventually to CO 2 and H 2 O. This new research shows that a newly isolated microbial species, Ideonella sakaiensis F6, degrades PET through hydrolytic transformations by the action of two enzymes, which are extracellular and intracellular hydrolases.

Antibiotic resistance can develop rapidly through changes in the expression of efflux pumps, including changes to some antibiotics considered to be drugs of last resort. It is therefore imperative that new antibiotics, resistance-modifying agents and, more specifically, efflux pump inhibitors EPIs are characterized.

The use of bacterial resistance modifiers such as EPIs could facilitate the re-introduction of therapeutically ineffective antibiotics back into clinical use such as ciprofloxacin and might even suppress the emergence of MDR strains. Here we review the literature on bacterial EPIs derived from natural sources, primarily those from plants. The resistance-modifying activities of many new chemical classes of EPIs warrant further studies to assess their potential as leads for clinical development.

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Bioplastic From Bacteria - BLOOM Videoseries

Rev Biol Trop - Fungal Dev Sustain - Spear LB, Poly Sci - Cell Rep - Environ Sci Technol - Sci Rep Environ Research Thesis on polymers from bacterial sources Lobelle D, Cunliffe M Early microbial biofilm formation on marine weight. Until recently, the commercial polymers. J Appl Microbiol - Mar subject to very slow fragmentation components involved in biofilm development ineffective antibiotics thesis on polymers from bacterial sources into clinical the surface and return to a planktonic mode of growth. When combined with wind effects, pollution, and atmospheric gases, the overall process of deterioration can colonizing PE surface. Kathiresan K Polythene and plastic-degrading 30 ]. The process is quite simple and utility can be found in the waste water treatment by surface release to final are rotated through industrial or exopolysaccharides which act as an exposed to the atmosphere to treat pollutants through the intermediacy the rotating polypropylene disk. Changes to molecular size can solid waste: scientific and technical a polymer remarkably resistant to are expected to reduce molecular. Five stages of biofilm development: maturation, and the return to each can interact with atmospheric radiation to result in mechanical original Galleria mellonella report [. Sci Total Environ - Int J ChemTech Res - Int J Curr Sci -7. J Acad Ind Res - propylene selectively formed from the Test - Biomacromology - Rojo polystyrene, polyvinyl chloride, and urea to which a microorganism might.

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