**1. Introduction**

Due to more than 200 years of industrialization and to the use of dangerous substances in many production processes, the countries across the world are facing the problem of soil, sediment, and water matrices contamination. Contaminated sites, namely environmental burdens, generally resulted in past and also arise nowadays from the manufacturing, storage, use, and disposal of hazardous chemicals and materials. It is now widely recognized that polluted sites pose threats to human health and the environment.

Polychlorinated biphenyls (PCBs) represent an environmental concern due to their hydrophobicity and toxicity. Although the production of PCBs has been banned and their use heavily restricted, they still pose an environmental problem due to their presence in old electrical transformers, capacitors, landfills, and in contaminated soil and sediments mainly in the areas around the former production facilities [1, 2]. Their physical and chemical properties such as thermal and chemical stability, resistance to degradation, and general inertness contribute to their persistence in the environment [3]. PCBs represent potential health risks for living organisms due to their lipophilic nature, bioaccumulation, and potential carcinogenic properties [4]. Hydroxylated PCBs (HPCBs), known PCB metabolites, have been detected in human serum samples and wildlife blood samples [5]. Numerous adverse health effects in human have been associated with these compounds. HPCBs are capable of mimicking a thyroid hormone, thyroxin [6], and may generate reactive oxidative species and cause DNA damage. Studies performed with the individual PCB congeners show that PCB toxicity and biodegradability are structure related as well [7].

Many conventional and sustainable remediation techniques have been invented to destroy hazardous organic pollutants [8]. The finding that both Gram-negative bacteria, such as *Achromobacter, Alcaligenes, Burkholderia, Commamonas, Pseudomonas*, and Gram-positive bacteria, such as *Bacillus, Corynebacterium*, and *Rhodococcus*, are able to degrade some PCB congeners opened the door to implement biological technologies. Bioremediation technologies using degradation capacity of microorganisms, mainly bacteria, have been seen ecological and economical alternative approach to physicochemical processes to eliminate diffusive contamination of persistent organic pollutants (POPs) in various environmental matrices, e.g., soil, sediments, and sludges. Bioremediation is an attractive, generally low-cost, innovative technology that is a sustainable approach to clean up organic compounds from contaminated areas. Bioremediation represents a perspective and prospective technique for treatment of polluted environments which involves usage of microorganisms and/or plants for pollutant biodegradation or biotransformation. The technology can be performed as natural attenuation or employed as an assisted bioremediation: biostimulation (addition of nutrients and inducers to fortify and stimulate the growth and metabolism of indigenous microorganisms), and bioaugmentation (introduction of indigenous or suitable exogenous bacteria to enhance biodegradation of relevant pollutant) [9–13]. However, successful soil bioaugmentation requires not only application of the individual bacterial strain or a bacterial consortium with the required degradation ability but also of the microorganisms able to survive in the adverse environment [14–17]. Poor survival of the inoculated microorganisms (usually bacteria) and low bioavailability of the hydrophobic carbon source are usually the main obstacles to the successful inoculum amendment. Moreover, the bottleneck for the successful catabolism of a recalcitrant hydrophobic compound is most often not the nature of the biochemical pathway for its degradation, but the overcoming of the endogenous and exogenous stress associated to the utilizing conditions. Although many bacteria have ability to metabolize, e.g., PCBs, high concentrations of these chemicals act as environmental stress factor and inhibit cell survival and then ability to metabolize these pollutants. If bacterial strains wanted to survive, they had to develop efficient adaptation mechanisms in the adverse environment [18, 19].

For the purpose to select the degradation-effective and adverse environment-resistant bacterial strain from 11 environmental isolates, obtained from the PCB-historically contaminated sediment and identified using molecular-biological methods [20], our research was focused on the study of adaptation mechanisms and responses of bioaugmented bacteria during the biological treatment of water and sediment matrices contaminated with PCBs. Since PCBs are highly hydrophobic, they may efficiently cross cell membrane through free diffusion. The effects of PCBs, chlorobenzoic acids (CBAs, PCB-biodegradation end products), biphenyl, and terpenes (the potential inducers of PCB degradation) on bacterial cytoplasmic membrane were determined [10, 11, 15, 19]. Only the resistant bacteria that possess the appropriate enzymes may play a major role in bioremediation technologies.
