'Plastic-eating' bacteria discovered by Indian scientists

Researchers have discovered two strains of 'plastic-eating' bacteria from the wetlands of Greater Noida, an advance that may lead to eco-friendly alternative clean-up methods for plastic waste worldwide. The bacterial strains discovered by researchers at Shiv Nadar University in Greater Noida, Uttar Pradesh, have the potential to decompose polystyrene a key component in Single-Use Plastic (SUP) items such as disposable cups, cutlery, toys, packaging materials etc.

The bacterial species namely Exiguobacterium sibiricum strain DR11 and Exiguobacterium undae strain DR14 were isolated from the wetlands adjoining the university.

Polystyrene is quite resistant to degradation due to its high molecular weight and long-chain polymer structure. This is the reason for their persistence in the environment, according to the study published in the journal Royal Society of Chemistry (RSC) Advances. The exponential production and consumption of polystyrene in various sectors has presented a great environment risk and raised the problem of waste management, the researchers noted.

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"Our data support the fact that strains of extremophile bacterium Exiguobacterium are capable of degrading polystyrene and can be further used to mitigate the environmental pollution caused by plastics," Richa Priyadarshini, Associate Professor at Shiv Nadar University, Greater Noida, told PTI.

"Wetlands are one of the richest habitats of microbial diversity but are relatively unexplored. Hence, these ecosystems are ideal grounds for isolating bacteria with novel biotechnological applications," said Priyadarshini who discovered the bacteria strains along with her team at the Department of Life Sciences, School of Natural Sciences.

According to industry estimates, India consumes about 16.5 million metric tonnes of plastic annually. The All India Plastic Manufacturers Association (AIPMA) estimates that the plastic industry produces about 14 million metric tonnes of polystyrene, which is non-biodegradable.

This effects both terrestrial and marine life, e.g. a plastic fork  can take up to 450 years or more to decompose, the researchers noted. In the universe of plastic items used daily, SUP constitutes about a fifth in volume, they said. The finding assumes significance in India given the recent announcement by the Prime Minister to eliminate SUP by 2022. The research team identified that upon coming into contact with the plastic (polystyrene), the two isolated bacteria strains use it as a carbon source, and create biofilms.

This alters the physical properties of polystyrene, and initiates a process of natural degradation with the release of hydrolysing enzymes to break the polymer chains. "Biodegradation is a process by which microbial organisms mainly bacteria and fungi transform or degrade chemicals introduced into the environment," Priyadarshini said.

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The team is currently trying to evaluate the metabolic processes of these strains for utilisation in the environmental bioremediation.

"What started as a scientific exploration of the wetland in our campus has led to this significant discovery of plastic-eating bacteria," said  Rupamanjari Ghosh, Vice-Chancellor, Shiv Nadar University.

"This is a dream solution of breaking plastic in a natural process and making it biodegradable," Ghosh said. "We started out by just exploring the area to get a sense of bacterial species prevalent in these areas, but ended up isolating numerous bacterial species with unique and useful properties," added Priyadarshini.

With new bacterial species being discovered with plastic biodegradation ability, she noted that novel enzymes and new potential metabolic pathways can be discovered which could help in bioremediation in future. The researchers noted that both Exiguobacterium strains were able to establish biofilms on polystyrenes surfaces. Biofilms are an assemblage of bacterial cells, which grow as communities, reaching to very high cell densities. This leads to more targeted and localised action of polymer degrading enzymes, the researchers said.

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"Polystyrene is quite recalcitrant to degradation and requires some form of pre-treatment like chemical, thermal, photo-oxidation etc prior to biodegradation," said Priyadarshini.

Both DR11 and DR14 strains were able to not only form biofilm on non-treated polystyrene but were also found capable of degrading unmodified plastic, researchers said.

"Human dependence on plastic material has increased substantially over the years, which has led to huge amount of plastic accumulation in the environment leading to adverse effects on the ecosystem," Priyadarshini said.

She noted that more sustainable methods for plastic degradation are required. The researchers note that the use of both indigenous and genetically modified bacteria could lead to eco-friendly alternative clean-up methods for plastic waste. Further research should be directed towards making these process faster, sustainable and cost-effective, they said.

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