Biochemical and genetic bases of microbial degradation of polychlorinated biphenyls (PCBs)

The microbial degradation of polychlorinated biphenyls (PCBs) has been exte nsively conducted by many workers, and the following general results have b een obtained, (1) PCBs are degraded oxidatively by aerobic bacteria and oth er microorganisms such as white rot fungi. PCBs are also reductively dehalo genated by anaerobic microbial consortia, (2) The biodegradability of PCBs is highly dependent on chlorine substitution, i.e., number and position of chlorine, The degradation and dehalogenation capabilities are also highly s train dependent, (3) Biphenyl-utilizing bacteria can cometabolize many PCB congeners to chlorobenzoates by biphenl-catabolic enzymes. (4) Enzymes invo lved in the PCB degradation were purified and characterized, Biphenyl dioxy genase, ring-cleavage dioxygenase, and hydrolase are crystallized, and two ring-cleavage dioxygenases are being solved by x-ray crystallography. (5) T he bph gene clusters responsible for PCB degradation are cloned from a vari ety of bacterial strains. The structure and function are analyzed with resp ect to the evolutionary relationship. (6) The molecular engineering of biph enyl dioxygenases is successfully performed by DNA shuffling, domain exchan ge, and subunit exchange. The evolved enzymes exhibit wide and enhanced deg radation capacities for PCBs and other aromatic compounds.