Polystyrene microplastics biodegradation by gut bacterial Enterobacter hormaechei from mealworms under anaerobic conditions: Anaerobic oxidation and depolymerization

Synthetic plastic is used throughout daily life and industry, threatening organisms with microplastic pollution. Polystyrene is a major plastic polymer and also widely found sources of plastic wastes and microplastics. Here, we report that Enterobacter hormaechei LG3 (CP118279.1), a facultative anaerobic bacterial strain isolated from the gut of Tenebrio molitor larvae (mealworms) can oxidize and depolymerize polystyrene under anaerobic conditions. LG3 performed biodegradation while forming a biofilm on the plastic surface. PS biodegradation was characterized by analyses of surface oxidation, change in morphology and molecular weights, and production of biodegraded derivative. The biodegradation performance by LG3 was compared with PS biodegradation by Bacillus amyloliquefaciens SCGB1 under both anaerobic and aerobic conditions. In addition, through nanopore sequencing technology, we identified degradative enzymes, including thiol peroxidase (tpx), alkyl hydroperoxide reductase C (ahpC) and bacterioferritin comigratory protein (bcp). Along with the upregulation of degradative enzymes for biodegradation, changes in lipid A and biofilm-associated proteins were also observed after the cells were incubated with polystyrene microplastics. Our results provide evidence for anaerobic biodegradation by polystyrene-degrading bacteria and show alterations in gene expression patterns after polystyrene microplastics treatment in the opportunistic pathogen Enterobacter hormaechei.