Microbial community capability of PCB degradation in marine sediments

Microbial communities are responsible for the geochemical cycles and bio-removal of organic compounds and xenobiotics playing a key-role in ecosystem functioning. They are able to adapt promptly to environmental changes and the presence of a natural microbial community is a necessary prerequisite for an effective response to the various chemicals that can contaminate an ecosystem. However, the recovery from contamination is only possible if toxicity does not hamper microbial activity. The knowledge of natural remediation capacity of a microbial community allows assessing the contaminant availability to higher levels in the ecosystem food web. Polychlorinated biphenyls (PCBs) are organic hydrophobic persistent pollutants which are found as diffuse contaminants both in soil and sediment. Bacteria are generally recognized as to be the main responsible of biological processes involved in the aerobic/anaerobic degradation of these pollutants. However, a complete PCB removal from environment still remains a very important issue to be investigated owing to their low bioavailability, co-presence of congeners differing in the number of chlorine atoms attached to the biphenyl rings, etc. In order to assess the natural attenuation capacity of bacterial communities living in seawater sediment, degradation experiments were carried out using PCB-contaminated sediments collected from La Spezia harbor (Italy). The experimental set consisted both of microbiologically active and sterile sediment microcosms, which were maintained over 6 months under aerobic or anaerobic conditions. Chemical and microbiological analyses were periodically performed and allowed to estimate the contaminant degradation kinetics and to evaluate the structure and the composition of the microbial communities selected under each experimental condition