Effects of Enzyme Hydrolysis in Biofilm Formation and Biotic Degradation on Weathered Bioplastics

As efforts to address plastic pollution increase, new avenues are opened for the use of biologically renewable and biodegradable plastics. With the influx of these new polymer systems, it is crucial to understand the degradation processes of these polymers, particularly through disposal systems designed to manage their waste (i.e., compost). This work seeks to characterize a multistep biodegradation system by studying how enzymatic hydrolysis impacts the formation of biofilms upon weathered biodegradable aliphatic polyesters to better understand processes that should occur in composting. Poly l-lactic acid (PLLA), after varying amounts of photochemical weathering, was exposed to the esterase proteinase K followed by exposure to suspended facultative anaerobe, Shewanella oneidensis, whose biofilms were quantified with crystal violet staining. Enzymatic hydrolysis was observed to promote the formation of a biofilm regardless of enzymatic concentration, enzyme exposure time, and state of weathering on the polymer. This trend also held true for a less commercially viable polymer like poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which was demonstrated to be resistant to enzymatic hydrolysis. Further, we observed that the state of photochemical weathering caused variable impacts to the biodegradation of PLLA. Polymer characterization suggests that while there are changes in crystallinity and surface accessible ester linkages, increased surface area caused by photodegradation and/or enzyme hydrolysis drives the observed trends. Overall, this work demonstrates a multistep biodegradation process is more effective at breaking down biodegradable polymers than a single biotic agent, though polymer weathering influences breakdown to some extent, offering insight into the importance of managing these waste streams to ensure optimal designed biodegradability.