Degradability of commercial mixtures of polychlorobiphenyls by three Rhodococcus strains.

Biodegradative characteristics were investigated for the commercially available mixtures of polychlorinated biphenyls (PCBs) Trikhlorbifenil and Sovol degraded by the Rhodococcus wratislaviensis КT112-7, Rhodococcus wratislaviensis CH628 and Rhodococcus ruber P25 strains isolated from the natural habitats. For bioutilization of the Trikhlorbifenil, all three strains were found to have a high biodegrading potential: the complete destruction was achieved in 10-14 days. For the mixture Sovol, the bioutilization parameters were found to be of lower values: the degradation of the PCBs congeners was 96-98% after 14 days. For the tested polychlorobiphenyl mixtures, the structural specificities of congeners are discussed, the genes encoding monooxygenases are revealed, and explanation is given to the differences in biodegradative characteristics of the Rhodococcus strains towards di-, tri-, tetra-, penta-, hexa- and heptachlorobiphenyls. The presented data are highly relevant for environmental remediation of objects polluted with the extremely hazardous polychlorobiphenyls.

Biodegradation of trichlorobiphenyls and their hydroxylated derivatives by Rhodococcus-strains.

A possibility of using a complex approach is considered to explain features of biodestruction of polychlorinated biphenyls (PCBs), which are known to be persistent organic pollutants. The approach comprises the following main stages: (i) chemical modification of chloroarenes by hydroxylation and (ii) bacterial degradation of the hydroxylated derivatives. This approach is applicable to individual trichlorobiphenyls (PCB 29, PCB 30) and to a widespread mixture Trikhlorbifenil (analog of Aroclor 1242 and Delor 103). As bacterial strain destructors, the Rhodococcus-strains (КТ112-7, СН628, P25) were used. It was established that the main metabolites of microbial biodegradation of both polychlorobiphenyls and their hydroxy derivatives are polychloro- and hydroxy(polychloro)benzoic acids, which allows an assumption to be made about possible further biodegradation of these compounds down to the products of the base exchange reaction in a cell: water, carbon dioxide and chlorine compounds. The study discusses the effect that the structure of PCBs congeners causes on the conversion by hydroxylation, on the biodegradation rate of both PCBs and their hydroxy derivatives, and on the metabolite formation levels.

Biodegradability of hydroxylated derivatives of commercial polychlorobiphenyls mixtures by Rhodococcus-strains.

For the first time, investigations are is carried out for the interactions of hydroxylated polychlorobiphenyls (HO-PCBs) mixtures, which were obtained from PCBs commercially available under the trade name Sovol, with the Rhodococcus (R.) strains. It is established that the HO-PCBs mixtures containing basic products within the range of 83.2-95.8% cause a toxic effect on the growth of R. wratislaviensis KT112-7, R. wratislaviensis CH628, R. ruber P25 strains. The inhibitory concentration (IC50) was varied within the range of 30-490 mg/l. For the first time, it is found that the bacterial strains can use HO-PCBs as a source of carbon with no co-substrate added. The strains are shown to degrade 95.5-100% of the HO-PCBs mixtures at a concentration of 0.1 g/l during 14 days. It is demonstrated that HO-PCBs degrading occurs following the classical bacterial pathway of transforming biphenyl/PCB. However, the HO-PCBs metabolites, which are substituted benzoic acids, are not the final products of the transformation and are subjected to further degrading by the strains. Therefore, the R. wratislaviensis KT112-7, R. wratislaviensis CH628, and R. ruber P25 strains are shown to degrade the HO-PCBs mixtures efficiently and are found to be stable to their toxic action.

Reactivity of polychlorinated biphenyls in nucleophilic and electrophilic substitutions.

To explain the chemical reactivity of polychlorinated biphenyls in nucleophilic (S(N)) and electrophilic (S(E)) substitutions, quantum chemical calculations were carried out at the B3LYP/6-31G(d) level of the Density Functional Theory in gas phase. Carbon atomic charges in biphenyl structure were calculated by the Atoms-in-Molecules method. Chemical hardness and global electrophilicity index parameters were determined for congeners. A comparison of calculated descriptors and experimental data for congener reactivity in the S(N) and S(E) reactions was made. It is shown that interactions in the S(N) mechanism are reactions of the hard acid-hard base type, these are the most effective in case of highly chlorinated substrates. To explain the congener reactivity in the SE reactions, correct descriptors were not established. The obtained results can be used to carry out chemical transformations of the polychlorinated biphenyls in order to prepare them for microbiological destruction or preservation.