Abstract

The accumulation of polylactic acid (PLA) microplastics (MPs) in estuaries presents significant environmental challenges. The potential biodegradation of PLA MPs was rarely studied in estuarine sediments from urban areas. This study examined PLA MPs biodegradation during enrichment and assessed microbial diversity and functional gene shifts between raw estuarine sediment (day 0) and enriched culture (day 60). The enriched culture at 60-day post-incubation reduced the 40 % weight of the initial 2 g L⁻¹ PLA MPs, accompanied by a decrease in the carbonyl peak at 1747 cm⁻¹, indicating oxidative polymer chain cleavage. In addition, the biodegradation process significantly altered microbial diversity and promoted key synergistic genera such as Symbiobacterium, Sphingobacterium, Comamonas, Pseudomonas, and Alcaligenes for cooperative PLA MPs biodegradation. Linear discriminant analysis scores highlighted the distinct differences in microbial profiles between the raw estuarine sediment and the enriched culture. In addition, functional genes including pht2, tphA2, putative chitinase, esterase, and lipase were enriched, which would facilitate biopolymer and phthalate degradation. These findings revealed how PLA MP exposure affected microbial carbon and nitrogen metabolism in estuarine sediment and uncovered synergistic bacterial taxa with biotechnological potential for sustainable plastic waste treatment.