Molecular mechanisms underlying synergistic polylactic acid degradation in a bacterial co-culture

Although synergistic interactions among environmental microbial communities are known to play essential roles in plastic biodegradation, the mechanisms underlying metabolic interactions among polylactic acid (PLA)-degrading bacteria remain elusive. Here, we bridged this knowledge gap by integrating microbial community succession, genomics, transcriptomics, and metabolomics to elucidate the cooperative degradation mechanisms of PLA-degrading bacteria. During community succession, Proteobacteria and Actinobacteriota became dominant, with their combined relative abundance increasing from 52% to 97%. From the enriched community, five PLA-degrading strains were isolated, among which Pseudomonas putida and Delftia sp. exhibited the highest co-culture degradation efficiency (18.7% reduction in carbonyl index). 2D correlation spectroscopy and LC-MS confirmed preferential cleavage of PLA chains at C-O-C bonds, leading to the formation of oligomers composed of lactic acid units. Genome annotation revealed that both species exhibited similar metabolic functions and possessed PLA degradation-related genes such as lldD encoding lactate dehydrogenase. Integrated transcriptomic-metabolomic analyses further demonstrated that co-culture enhanced PLA degradation through bidirectional metabolite exchange. Pseudomonas putida acted as the primary degrader, with lldD upregulated 4.9-fold, and supplied Delftia sp. with central carbon intermediates (e.g., fructose-6-phosphate) and amino acids (tryptophan, glutamine). Conversely, Delftia sp. showed a 2.7-fold downregulation of lldD and reciprocally provided Pseudomonas putida with amino acids (arginine, serine, cystine). Collectively, this study uncovers the molecular basis of synergistic PLA degradation and provides new insights into microbial cooperation within the plastisphere, offering a foundation for designing microbial consortia to mitigate plastic pollution and promote sustainable environmental management.