Plastics: Microbial Degradation, Environmental and Biotechnological Perspectives

Plastics are widely used in our economy and each year, at least 350-400 million tons are being produced. Due to poor recycling and low circular use, millions of tons accumulate annually in terrestrial or marine environments. Today it has become clear that plastic causes adverse effects in all ecosystems and that microplastics are of particular concern to our health. Therefore, recent microbial research has addressed the question, if and to which extent microorganisms can degrade plastics in the environment. This review summarizes current knowledge on microbial plastic degradation. Enzymes available act mainly on the high molecular weight polymers of polyethylene terephthalate (PET) and ester-based polyurethane (PUR). Unfortunately, the best PUR- and PET-active active enzymes and microorganisms known still have moderate turnover rates. While many reports have been published describing microbial communities degrading chemical additives, no enzymes acting on the high molecular weight polymers polystyrene, polyamides, polyvinylchloride, polypropylene, ether-based polyurethane and polyethylene are known. Altogether these polymers stand for more than 80 % of the annual plastic production. Thus, further research is needed to significantly increase the diversity of enzymes and microorganisms acting on these polymers. This can be achieved by tapping into the global metagenomes of non-cultivated microorganisms and dark matter proteins. Only then, novel biocatalysts and organisms can be delivered that allow rapid degradation, recycling or value-added use of the vast majority of most man-made polymers.