Plastics: Environmental and Biotechnological Perspectives on Microbial Degradation

Abstract

Plastics are widely used in the global economy, and each year, at least 350 to 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 of if and to what 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 enzymes and microorganisms known still have moderate turnover rates. While many reports describing microbial communities degrading chemical additives have been published, no enzymes acting on the high-molecular-weight polymers polystyrene, polyamide, polyvinylchloride, polypropylene, ether-based polyurethane, and polyethylene are known. Together, these polymers comprise more than 80% of 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 noncultivated microorganisms and dark matter proteins. Only then can novel biocatalysts and organisms be delivered that allow rapid degradation, recycling, or value-added use of the vast majority of most human-made polymers.

Growing a circular economy with fungal biotechnology: a white paper

“…Millions of tons of plastics accumulate in the environment annually due to their stability, poor recycling and low circular use, and they represent an ecological threat to nature and human health. At least 350-400 million tons of plastics are being produced annually worldwide [70], while its production keeps increasing by an average of 7% per annum. In 2014, for example, 311 million tons were produced, among these, 59 million tons in Europe.…”

“…Among the most promising enzymes used for PET and polyurethane treatment have been esterases, cutinases, lipases and lignin-modifying and unspecific macromoleculedepolymerising and hydrolytic enzymes, such as different peroxidases, laccases, glucose oxidases and cytochromes P450. However, no distinct degradation effects for virgin and pre-treated plastics have been achieved solely by the use of pure enzymes [70]. Hence, currently ongoing research is focused on mycelial-based degradation (whole cell degradation) of pure or mixed cultures in combination with purified enzyme cocktails.…”

Unraveling 1,4-Butanediol Metabolism in Pseudomonas putida KT2440

“…In the context of a bio-upcycling strategy, bacteria and fungi have been found to degrade PU, including several Pseudomonads which grow on PU at high rates (Howard, 2002). A range of PU-degrading ester-and urethane hydrolases have been identified (Hung et al, 2016;Schmidt et al, 2017;Danso et al, 2019;Magnin et al, 2019a,b). Besides this, chemical recycling of PU is also possible with more mature technologies (Zia et al, 2007;Behrendt and Naber, 2009).…”

Method for Zero-Waste Circular Economy using worms for plastic agriculture: Augmenting polystyrene consumption and plant growth

“…There are exciting research based on enzymes isolated from bacteria present in plastic eating worms [27][28][29][30] , but the implementation of these process towards complete degradation into harmless substances at industrial scale will still require further research and engineering in the face of an increasingly pressing problem of plastic waste. In the meantime, the natural solution of worms can be investigated for more immediate implementation, especially given that they can also simultaneously provide for urban farming in both fish/poultry feed and their frass for food crops.…”