An overview of plastic degradation using microbes

An overview of plastic degradation using microbes
Plastic is the most disastrous substance present in our society that causes an immense amount of pollution. Scientists have been working on many ways to reduce the effects caused by plastics since they cannot be destroyed easily. The hydrogen bonding between plastic is so strong that it can be only denatured by thermal heat, in turn releasing pollutants into the atmosphere. Hence, various ways of degrading plastic by biological substances are being studied and microbes have shown promising results to be efficient in degrading plastic.

Polyethylene and polyurethane are the plastics that are widely used in the present society. Polyethylene is made up of monomers of ethylene and polyurethane is made up of polyisocyanate and polyol linked by urethane. Microbes produce certain enzymes like protease, laccase and esterase. Bacteria and fungi are efficient plastic degraders but fungi are being more efficient.

The degradation of plastics takes place in a step-wise process. Plastic biodeterioration is the first step involved in plastic biodegradation. It will alter the plastics’ physical properties by enlarging the pores with the help of extracellular enzymes. Most of the microbes will form a biofilm over the plastics since they are hydrophobic in nature; the organism adhering to it should also be hydrophobic.

Biofragmentation is the next process involved in plastic biodegradation. It converts the plastics into monomers of less molecular weight since it cannot pass as such through the cell membrane. Plastics are generally stable and they should have an unstable electric charge for lysis to occur. Microbes secrete oxygenase which adds oxygen to the carbon chains destabilising the polymers.

Assimilation and Mineralisation is the last step involved in biodegradation. Assimilation refers to the assimilation of monomers inside the cell wall releasing secondary metabolites, these metabolites will be used by other cells for metabolic activities. All the compounds get mineralised and release gases.

Various studies have proved that Streptococcus, Staphylococcus, Achromobacter xylooxidans, Pseudomonas sp. and Comomonas acidovorans can degrade plastic materials efficiently. Fungal species like Aspergillus niger, Penicillium, Saccharomyces cerevisae and Aspergillus glaucus are also efficient plastic degraders. It takes about 9 months for the degradation of plastic in case of bacteria isolated from soil; lesser time period is consumed by fungi, i.e. almost one month. These organisms use plastic as the sole source of carbon.

Endophytic fungi called Pestaliopsis microspora isolated from the wood bark of Ecuadorian rainforest was able to degrade polyurethane within 10 days of incubation. It produces serine hydrolyase which cleaves the urethane linkages making it degrade at a faster rate. The bacterial organism like Pseudomonas chloraphilis also degrades polyurethane by producing esterase.

There are various organisms present in the ecosystem with novel characters that are yet to be exploited. The screening of the organisms is an important factor to understand their novelties. Plastic degradation using microbes is a cost-efficient and economical way to reduce pollution.

How to cite this article:
Malavika Menon. An overview of plastic degradation using microbes . BioLim O-Media. 29 June, 2016. 4(6).
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