THE BIPHENYL POLYCHLORINATED BIPHENYL-DEGRADATION LOCUS (BPH) OF PSEUDOMONAS SP LB400 ENCODES 4 ADDITIONAL METABOLIC ENZYMES

The bph locus of Pseudomonas sp. LB400, encoding biphenyl/polychlorinated biphenyl (PCB) degradation, contains a region of about 3.5 kb of hitherto unknown function, between bphC and bphD. This DNA segment has now been characterized. Four structural genes have been located and identified by a combination of expression cloning, enzyme activity tests and DNA sequencing. The region contains four closely spaced cistrons (bphKHJI) encoding a glutathione S-transferase (GST), a 2-hydroxypenta-2,4-dienoate hydratase, an acetaldehyde dehydrogenase (acylating) and a 4-hydroxy-2-oxovalerate aldolase, respectively. The latter three are enzymes required for conversion of the aliphatic end product of bphABCD-encoded catabolism of biphenyls to Krebs cycle intermediates. The discovery of these genes provides a rationale for growth of the strain on chlorinated biphenyls which yield chlorinated benzoates as dead-end metabolites. The sequences of the enzymes involved are 54-71% identical to those of homologous enzymes encoded by the dmp and xyl operons. The role of the GST in the degradation of biphenyls is less clear, but since it was found to contain, in the putative xenobiotic substrate-binding domain, a region which shares about 29% of identical amino acids with a bacterial tetrachlorohydroquinone dehalogenase, it may be involved in dehalogenation of PCB-degradative intermediates.