Changed bacterial community in the river water samples upon introduction of biodegradable poly(3-hydroxybutyrate)

The addition effects of polymeric materials on natural environments have been mainly evaluated in terms of the relationships between culturable polymer-degrading microorganisms and/or their secreted enzymes and target materials. In this study, we applied metagenome analysis to better understand the change in unculturable microorganismal biodiversity in the four different river samples by using poly (3-hydroxybutyrate) [P(3HB)], a well-studied biodegradable polymer. An inverse relationship between the number of microorganisms and the weight of P(3HB) was observed for all the river samples, while no changes were observed for nondegradable polyethylene. Based on statistical analysis (Chao1 index), the microbial consortia exhibited reduced diversity and tended to converge to similar microbial communities among three of the river samples. This suggests a tight relationship between the biodegradation of P(3HB) and bacterial consortium structure in the river environments. Interestingly, metagenomic sequences corresponding to bacteria that have already been identified as culturable P(3HB) degraders were detected, suggesting a close relationship between the unculturable community and the culturable community. The metagenomic analysis has provided us useful insights into the dynamic changes in the microbial community in the river samples and is applicable for various combinations of environments and biopolymers.