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.

Risk assessment of change in respiratory gas concentrations by native culturable bacteria in the air of sulfide ore mines

Sulfide ores are extracted from mines at considerable depths, that having unique a physical and chemical environment. On the one hand, physical, chemical, and biological processes taken place in the rocks produce this environment; on the other hand, they form unique bacterial communities. The aim of this study was to study the native culturable aerobic bacteria present in the sulfide ores of the deposits located in the Krasnoyarsk Territory (Russia) and evaluate their activity in relation to respiratory gases (oxygen and carbon dioxide) present in air. The results of the study established that the culturable bacteria present in the sulfide ore of the N1 deposit were related to genera Bacillus and Paenibacillus (class Bacilli), genera Citricoccus, Micrococcus, Brachybacterium, Microcella, Dietzia, and Rhodococcus (class Actinomycetia) and genera Paracoccus and Pseudomonas (class Proteobacteria). The culturable bacteria of the N2 sulfide ore deposit were represented by genera Bacillus, Oceanobacillus, Alicyclobacillus (class Bacilli) and genera Micrococcus and Agromyces (class Actinomycetia). The N2 deposit community contained the strain Nor9-1, which showed a high level of similarity with the Alicyclobacillus aeris ZJ-6 iron-/sulfur-oxidizing bacterium. The model systems showed a strong correlation (r² = 0.91-0.97) between the growth of the bacterial communities of the studied ores and changes in the concentrations of oxygen and carbon dioxide in the model atmosphere. Under the ecological optimum (specific growth rate of the culture constituting 0.519 d^-1) in 7 d, oxygen decreased to 0.34-1.48% and carbon dioxide increased to 7.44-14.88%. Under the ecological pessimum (restricted available organic carbon), given the predominant development of the chemolithotrophic group of bacteria (specific growth rate of 0.045 d^-1), changes in the respiratory gas concentrations constituted 0.9-2.7% of O₂ and 0.06-0.16% of CO₂. A relationship was established between the specific rate of O₂/CO₂ loss and specific growth rate of the bacterial communities. Thus, for the first time, indigenous cultivated aerobic bacteria of sulfide ores collected from the deposits of the Krasnoyarsk Territory were studied, and their effects on oxygen and carbon dioxide contents in the atmosphere of closed model systems were examined.

Selective pressure of biphenyl/polychlorinated biphenyls on the formation of aerobic bacterial associations and their biodegradative potential

Unique bacterial associations were formed in the polluted soils from territory of the industrial factories Open Joint Stock Company "The Middle Volga Chemical Plant," Chapaevsk, Russia and Open Joint Stock Company "Lubricant Producing Plant," Perm, Russia. This study evaluates the influence of the biphenyl/polychlorinated biphenyls (PCB) on the formation of aerobic bacterial associations and their biodegradative potential. Enrichment cultivation of the soil samples from the territories of these industrial factories with PCB (commercial mixture Sovol) was lead for forming aerobic bacterial enrichment cultures showing a unique composition. The dominating in these bacterial cultures was the phylum Proteobacteria (Beta- and Gammaproteobacteria). Using biphenyl as a carbon source led to decrease of biodiversity in the final stable bacterial associations. Periodic cultivation experiments demonstrated that the association PN2-B has a high degradative potential among the six studied bacterial associations. PN2-B degraded 100% mono-chlorobiphenyls (94.5 mg/L), 86.2% di-chlorobiphenyls (22.3 mg/L), 50.9% Sovol, and 38.4% Delor 103 (13.8 mg/L). Qualitative analysis of metabolites showed that association performed transformation of chlorobenzoic acids (PCB degradation intermediates) into metabolites of citrate cycle. Twelve individual strain-destructors were isolated. The strains were found to degrade 17.7-100% PCB1, 36.2-100% PCB2, 18.8-100% PCB3 (94.5 mg/L), and 15.7-78.2% PCB8 (22.3 mg/L). The strains were shown to metabolize chlorobenzoic acids formed during degradation of chlorobiphenyls. A unique ability of strains Micrococcus sp. PNS1 and Stenotrophomonas sp. PNS6 to degrade ortho-, meta-, and para-monosubstituted chlorobenzoic acids was revealed. Our results suggest that PN2-B and individual bacterial strains will be perspective for cleaning of the environment from polychlorinated biphenyls.

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.