Waste management is one of the biggest tasks wherever humans thrive and in particular with the most commonly used non-biodegradable and accumulating waste- plastic. Technically, polymers such as polyethylene, PVC, nylon make the synthetic plastic. Due to its malleability and ability to acquire any shape, reasonably light weight and low cost along with durability makes it popular and widely used. Although it is easy to dump plastic it persists in the environment and is difficult to degrade or even reuse. Quite often it is simply disposed into the oceans. According to an article on the Daily News, by 2050, there will be more plastic in the oceans than fishes. This poses a serious threat to the environment especially in the developing economy like India where waste management is not yet robust. In recent times, quite interestingly, there have been discovery of certain biological species which are able to digest plastic in one way or another. Here we explore three such species
1) Bacteria: Ideonella sakaiensis
I. sakaiensis is Gram-negative, aerobic, and rod-shaped bacteria. A team of researchers from Kyoto Institute of Technology and Keio University in the year 2016 isolated this organism from samples of plastic collected outside a plastic recycling institution. Using a combination of two enzymes this organism degrades polyethylene. First it uses PETase to break down the PET plastic in presence of water. And then it further breaks down plastic using the enzyme MHETase into terephthalic acid and ethylene glycol, again with the help of water. Unlike the PET plastic, none of these final products pose a threat to environment.
2) Fungus: Pestalotiopsis microspora
Pestalotiopsis microspora is a species of the endophytic (living within a plant for at least part of its life cycle) fungus which is able to break down and digest polyurethane (PUR). This fungus was discovered in the year 2011 by leading biochemist Scott A. Strobel and were found able to grow on PUR as the sole carbon source under both aerobic and anaerobic conditions. Polyurethanes are used extensively in the making of foam, wheels, tires and synthetic fibers (like Spandex). Pestalotiopsis produces the enzyme Serine hydrolases which carries out degradation of PUR making it a potential candidate for bioremediation.
3) Worm: Galleria mellonella
Federica Bertocchini, from the Spanish National Research Council (CSIC) and biochemists Paolo Bombelli and Christopher Howe from University of Cambridge, found that the larvae of the common insect Galleria mellonella (greater wax moth) fed on polyethylene bags. In an experiment, about 100 worms were exposed to a plastic supermarket bags. In about half a day plastic mass of 92 milligrams was reduced. The overall rate of reduction was much faster than the bacteria discovered at Kyoto University. In the wild these wax-worms feed on honeycomb. After eating, the waste eliminated by these worms can be readily converted into useful substances such as antifreeze.
Galleria mellonella larvae
Traditional methods of tackling the ‘plastic problem’ have several approaches. These includes chemical treatment like chemical oxidation with chromic acid, nitric acid, and peroxides or etching with a strong base like sodium or potassium hydroxide. Segregating of wastes before dumping and developing cleaner alternatives like the use of paper or banana leaves etc. The biological method, in any case, can be much quicker, efficient, cleaner and less risky. It does need more systematic investigations and further development to fully exploit the plastic eater’s abilities.