Site-specific response of sediment microbial community to supplementation of polyhydroxyalkanoates as biostimulating agents

The use of biodegradable plastics is constantly raising and the effects on the ecosystems of their environmental accumulation are still to be thoroughly explored. In a previous study, we provided a first, lab-scale glance on the possible utilization of the biopolymers polyhydroxyalkanoates (PHAs) as stimulating agents to enhance microbial degradation of polychlorobiphenyls (PCBs) in marine sediments coming from Pialassa della Baiona (Ravenna, Italy), as a model of challenging contaminated environment. Here, the same approach was applied to a heavily polluted sediment of Mar Piccolo (Taranto, Italy) and results were compared both in terms of bioremediation efficiency and impact on metabolic and compositional features of the resident microbial community. We reported a decreased efficiency of PHA in stimulating PCB dechlorination in sediments from Taranto. However, the comparative approach provided an insight on the secondary effects of PHAs on the surrounding ecosystem, with changes in the abundance of primary degraders caused by the presence of an exogenous carbon source, consequently affecting also the abundance of subdominant bacteria, possibly cross-feeders. Differences in features of the sediments (i.e. granulometry, peculiarities of the mixed chemical contamination, indigenous microbial community) could have influenced the observed differences in resulting anaerobic metabolism. This study contributes at clarifying the environmental impact of accumulating biopolymers. Acting as carbon and energy source, these molecules will differently shape the microbial community according to the studied sediment, affecting the extent of remediation actions in case of their deliberate dispersion as biostimulating agents.