Recent advances in the biodegradation of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are typical lasting organic pollutants. Persistence and recalcitrance to biodegradation of PCBs have hampered the transformation of PCB congeners from the environment. Biological transformation of polychlorinated biphenyls could take place through anaerobic dechlorination, aerobic microbial degradation, and a combination of transformation of anaerobic dechlorination and aerobic degradation. Under anaerobic conditions, microbial dechlorination is an important degradation mode for PCBs, especially high-chlorinated congeners. The low-chlorinated compounds formed after reductive dechlorination could be further aerobically degraded and completely mineralized. This paper reviews the recent advances in biological degradation of PCBs, introduces the functional bacteria and enzymes involved in the anaerobic and aerobic degradation of PCBs, and discusses the synergistic action of anaerobic reduction and aerobic degradation. In addition, the different ways to the microbial remediation of PCBs-contaminated environments are discussed. This review provides a theoretical foundation and practical basis to use PCBs-degrading microorganisms for bioremediation.

Regional analysis of potential polychlorinated biphenyl degrading bacterial strains from China

Polychlorinated biphenyls (PCBs), the chlorinated derivatives of biphenyl, are one of the most prevalent, highly toxic and persistent groups of contaminants in the environment. The objective of this study was to investigate the biodegradation of PCBs in northeastern (Heilongjiang Province), northern (Shanxi Province) and eastern China (Shanghai municipality). From these areas, nine soil samples were screened for PCB-degrading bacteria using a functional complementarity method. The genomic 16S rDNA locus was amplified and the products were sequenced to identify the bacterial genera. Seven Pseudomonas strains were selected to compare the capacity of bacteria from different regions to degrade biphenyl by HPLC. Compared to the biphenyl content in controls of 100%, the biphenyl content went down to 3.7% for strain P9-324, 36.3% for P2-11, and 20.0% for the other five strains. These results indicate that a longer processing time led to more degradation of biphenyl. PCB-degrading bacterial strains are distributed differently in different regions of China.

Whole-Genome Sequence of Aquamicrobium sp. Strain SK-2, a Polychlorinated Biphenyl-Utilizing Bacterium Isolated from Sewage Sludge

Here, we report the whole-genome sequence of Aquamicrobium sp. strain SK-2, a bacterium which can use 2,2',4,4',5,5'-hexachlorobiphenyl as the sole carbon source for its growth. An approximately 9.23-Mb genome sequence of SK-2 will greatly facilitate research efforts regarding the study of the polychlorinated biphenyl (PCB) degradation mechanism.

Polychlorinated biphenyls (PCBs) in Africa: a review of environmental levels

Several studies have shown an increase in PCB sources in Africa due to leakage and wrongly disposed transformers, continuing import of e-waste from countries of the North, shipwreck, and biomass burning. Techniques used in the recycling of waste such as melting and open burning to recover precious metals make PCBs contained in waste and other semivolatile organic substances prone to volatilization, which has resulted in an increase of PCB levels in air, blood, breast milk, and fish in several regions of Africa. Consequences for workers performing these activities without adequate measures of protection could result in adverse human health effects. Recent biodegradation studies in Africa have revealed the existence of exotic bacterial strains exhibiting unique and unusual PCB metabolic capability in terms of array of congeners that can serve as carbon source and diversity of congeners attacked, marking considerable progress in the development of effective bioremediation strategies for PCB-contaminated matrices such as sediments and soils in tropical regions. Action must be taken to find and deal with the major African sources of these pollutants. The precise sources of the PCB plume should be pinned down and used to complete the pollutant inventories of African countries. These nations must then be helped to safely dispose of the potentially dangerous chemicals.

Isolation of biphenyl and polychlorinated biphenyl-degrading bacteria and their degradation pathway

Four strains of biphenyl-degrading bacteria were isolated from a sewage and identified from the Rhodococcus genus (SK-1, SK-3, and SK-4) and Aquamicrobium genus (SK-2) by 16S rRNA sequence. Among these strains, strain SK-2 was most suitable for biphenyl degradation. When 0.65, 1.3, 2.6, or 3.9 mM of biphenyl was used, the biphenyl was completely degraded within 24 and 96 h of culture, respectively. However, in the case of 6.5 and 9.75 mM of biphenyl, the biphenyl degradation yields were about 80 % and 46.7 % after 120 h of culture, respectively. The isolated strains could degrade a broad spectrum of aromatic compounds including high-chlorinated polychlorinated biphenyl (PCB) congeners in the presence of biphenyl. In addition, strain SK-2 could utilize PCB congeners containing one to six chlorine substituents such as 2,2',4,4',5,5'-hexachlorobiphenyl. The PCB utilization rate by the strain SK-2 was increased compared to that of other PCB congener-utilizing bacteria. The four isolates metabolized 4-chlorobiphenyl to 4-chlorobenzoic acid and 2-hydroxy-6-oxo-6-(4'-chlorophenyl)-hexa-2,4-dienoic acid. These results suggest the isolated strains might be good candidates for the bioremediation of PCB-contaminated soil, especially high-saline soils.