Bioremediation of PCB-Contaminated Sediments and Adaptive Mechanisms of Bacterial Degraders Exposed to Polychlorinated Biphenyls (PCBs)

Abstract

In the recent decades, several hundred tons of polychlorinated biphenyls (PCBs) have been released into the environment. Due to their hydrophobic properties, PCBs tend to be adsorbed by natural organic matter in the aqueous bottom sediments. Sediment is an essential, integral part of the hydrological system. However, because sediments are the ultimate reservoir for the numerous chemical contaminants, they have the potential to pose ecological and human health hazard. Environmental and economic reasons have urged the development of bioremediation technologies for PCB removal from the contaminated areas. This contribution is focused on biodegradation of PCBs in contaminated sediments using biostimulation and bioaugmentation approaches of bioremediation, as well as on the effects of PCBs as the potential stress factors on the cell membrane of the bacterial degraders and on the membrane adaptation mechanisms. Determination of ecotoxicity and genotoxicity of PCB-contaminated sediments represents an important part of our research together with isolation and identification of PCB-degrading bacterial strains from the sediments. The obtained results indicate beneficial effect of both biostimulation and bioaugmentation strategies during biodegradation of PCBs in the contaminated sediments. PCBs affected saturation of membrane fatty acids, cis–trans isomerization, caused pronounced adaptation changes, and altered membrane fluidity of the cells of the bacterial degraders. This phenomenon is thought to be the major adaptive mechanism in microorganisms exposed to toxic aromatic pollutants. Study of ecotoxicity demonstrated that sediments sampled from industrial canal and water reservoir, both located in the vicinity of the former producer of PCBs in Slovakia, were toxic for the tested bioindicators. It has been established that PCB-contaminated sediments represent a source of adverse effects on life functions of the biota. Eleven bacterial strains were isolated and identified in the contaminated sediments using 16sRNA method. Detection of bphA gene encoding biphenyldioxygenase, the important starting enzyme of PCB degradation, was performed. Data obtained from microcosm studies might be useful in the preliminary design of a site-specific biostimulation/bioaugmentation strategy.