Natural and synthetic polymers represent a challenging source of raw materials to harvest and control in our environment. All polymeric materials eventually deteriorate and degrade over time due to changes in the inter-or intramolecular bonding resulting from biological and/or environmental exposure. Microorganisms use a combination of cellular hydrolytic and oxidative chemical processes to release carbon sources from polymers. Specifically, polyesters and polyurethanes are susceptible to hydrolysis by catabolic enzymes released by fungi, bacteria and archaea in the environment, and these polymer classes make up 35% of global polymer production. This review focuses on the activity of lipases, cutinases, esterases and proteases with polyesters and polyurethanes reported in articles from 2018 or later as well as new advances and key trends in both fundamental and applied biodegradation research efforts.

Aims: Biochemical hydrolysis and chemical catalysis are involved in the successful biodegradation of polymers. In order to evaluate the potential separation between biochemical and chemical catalysis during the biodegradation process, we report the use of two diphenylpolyenes (DPPs), all trans-1,4-diphenylbutadiene (DPB) and all trans-1,6-diphenylhexatriene (DPH), as potential acid-sensitive indicators in polymers. Methods and Results: 1,4-Diphenylbutadiene and DPH (0.1% w/w) were melt-cast successfully with poly(ethylene succinate) hexamethylene (PES-HM) polyurethane (thermoset polyester polyurethane) coatings above 80℃. When these two DPP/ PES-HM coatings were exposed to a concentrated supernatant with significant esterase activity resulting from the growth of a recently isolated and identified strain of Tremellomycetes yeast (Naganishia albida 5307AI), the DPB coatings exhibited a measurable and reproducible localized decrease in the blue fluorescence emission in regions below where hydrolytic biodegradation was initiated in contrast with DPH blended coatings. The fluorescence changes observed in the biodegraded DPB coating were similar to exposing them to concentrated acids and not bases. Conclusions:Our experiments resulted in (1) a method to blend DPP additives into thermoset coatings, (2) the first report of the biodegradation of polyester polyurethane coating by N. albida, and (3) demonstration that hydrolytic supernatants from this strain generate acidic region within degrading polyester coatings using DPB as the indicator.Significance and Impact of the Study: Our experiments confirm that N. albida is an active polyester degrader and that DPB is a promising acid sensitive polymer coating additive.

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