Biodegradation of polystyrene and low-density polyethylene by Zophobas atratus larvae: Fragmentation into microplastics, gut microbiota shift, and microbial functional enzymes

Abstract

In this study, biodegradation of polystyrene (PS) and low-density polyethylene (LDPE) by Zophobas atratus larvae was characterized to investigate fragmentation of ingested polymers, larval physiology, gut microbiota, and microbial functional enzymes over a 28-day test. The larvae maintained high survival rates and low cannibal rates, but their body fat content decreased when fed with PS or LDPE with respective consumption rates of 43.3 ± 1.5 and 52.9 ± 3.1 mg plastics/100 larvae per day. The larvae biodegraded PS via broad depolymerization and LDPE via limited-extent depolymerization. The ingested PS and LDPE were fragmented into microplastics with a mean size of 174 and 185 μm on a volume basis, and the particles with a size of 6.3 and 5.9 μm reached a maximum number, respectively, with no nanoplastics generated. Chemical modifications of the polymers were confirmed. Significant shifts and clustering in the gut microbiota were detected with the relative abundance of Citrobacter sp. increasing when PS and LDPE were fed, as reported for other species of Tenebrionidae. Microbial functional enzymes, possibly associated with plastic degradation, including arylesterase and serine-hydrolase, were upregulated in both PS-fed and PE-fed larvae. This work provides new insights into insect-mediated biodegradation of persistent plastics for future investigations.