Rapid biodegradation of high molecular weight semi-crystalline polylactic acid at ambient temperature via enzymatic and alkaline hydrolysis by a defined bacterial consortium

Abstract

Biodegradation of polylactic acid (PLA) in the natural environment is usually slow. This study aims to develop a bacterial consortium that biodegrades semi-crystalline PLA films with high molecular weight, at an ambient temperature of 30 °C. PLA-degrading bacteria were enriched from polymeric wastes. Proteobacteria, Bacteroidia and Actinobacteria relative abundances were high during the PLA-enrichment process. Four isolated bacteria, Nocardioides zeae EA12, Stenotrophomonas pavanii EA33, Gordonia desulfuricans EA63, and Chitinophaga jiangningensis EA02, which synthesized PLA degradative enzymes such as protease, esterase and lipase were mixed as consortium EAc. PLA films inoculated with EAc showed biofilm formation (10.54 log CFU/cm2), molecular weight (Mv) reduction (61%), and weight loss (9.68%) after 35 days. The extent of biodegradation was significantly higher than that by individual strains. Decrease in PLA Mv fitted the first order kinetics with a rate constant of 0.028 d−1. UV spectroscopy of biodegraded PLA suggested the carbonyl bond cleavage, while substantial chain scissions in the ester backbone of PLA were detected by ATR-FTIR. The rapid PLA biodegradation was due to the synthesis of diverse hydrolases and increase in pH, which led to enzymatic and alkaline hydrolysis. Consequently, EAc consortium could be applied in general solid waste treatment facilities for PLA degradation.