Plastic degrading microbes

Plastic degrading microbes

Polythene terephthalate has been choking mother earth in recent decades. The best remedy to this could be to the biodegrade these plastics by plastic degrading microbes. However, there are various types of plastic degradation. They are biodegradation, mechano-chemical, catalytic, ozone induced and thermal biodegradation. The degradation process can take place both in aerobic and anaerobic conditions thus indicating that both aerobes and anaerobes can degrade plastics.

Research shows that the Indian mangrove soil harbours microbes which are capable of degrading plastics/polythene. Both gram positive and gram negative bacteria are involved in the process of biodegradation. Among fungi, Aspergillus are predominantly involved in this activity.

Gram positive bacteria:

• Streptococcus
• Staphylococcus
• Micrococcus

Gram negative:

• Moraxella
• Pseudomonas

Fungi:

• Aspergillus niger
• Aspergillus glaucus

All these microbes take minimum 8 weeks to 9 months to degrade plastics. There are various factors which influence the capacity of the microbes to degrade plastics. Degradation depends on both the physical and chemical nature of that polymers. Polymers with side chains, high molecular weight can be degraded slowly. Apart from this, their morphology, melting temperature, degree of crystallisation also play an important role in deciding their degradation ability.

However, Ideonella sakaiensis is capable of degrading a thin film of PET in 6 weeks at 30 degree centigrade. This bacterium degrades PET with the help of two enzymes, which act continuously in a sequence. First of all the bacterium adheres to PET and it produces an intermediate substance with two monomers-ethylene glycol and terephthaic acid through hydrolysis. The second enzyme further acts on this intermediate substance.

List of the microbes and the enzymes produced by them to degrade plastics.

• Alcaligens faecalis - polycaprolactone depolymerase
• Aureobasidium pullulans - extracellular esterase
• Rhizopus delemar - lipase
• Pestalotiopsis microspora - serine
• Comomonas acidivorans - esterane

Some of these microbes use plastics as their sole source of carbon and degrade them completely. Degradation of plastics can be identified by cracking, erosion, discolouration and phase separation.

Why harm the earth and then seek the solution of degradation?

Isn't it  better to  upgrade to bioplastics. Bioplastics are biodegradable plastics which are manufactured from fossils or from biomass. Though the manufacture of bioplastics is costly, it has several advantages than synthetic plastics.