ORGANIZATION OF THE BPH GENE-CLUSTER OF TRANSPOSON TN4371, ENCODING ENZYMES FOR THE DEGRADATION OF BIPHENYL AND 4-CHLOROBIPHENYL COMPOUNDS

Tn4371 is a 55 kb transposon which encodes enzymes for the degradation of biphenyl and 4-chlorobiphenyl compounds into benzoate and 4-chloro benzoate derivatives. We constructed a cosmid library of Tn4371 DNA. T he bph genes involved in biphenyl/4-chlorobiphenyl degradation were fo und to be clustered in the middle of the transposon. Sequencing reveal ed an organisation of the bph genes similar to that previously found i n Pseudomonas sp. KKS102, i.e. the bphEGF genes are located upstream o f bphA1A2A3 and bphA4 is separated from bphA1A2A3 by bphBCD. Consensus sequences for sigma 54-associated RNA polymerase were found upstream of bphA1 and bphEGF. Plasmid RP4::Tn4371 was transferred into a mutant of Alcaligenes eutrophus H16 lacking sigma 54. In contrast to wild-ty pe H16 exconjugants, the sigma 54 mutant exconjugants could not grow o n biphenyl, indicating the dependence of Tn4371 bph gene expression on sigma 54. The Tn4371-encoded bph pathway was activated when biphenyl and various biphenyl-like compounds were present in the growth medium. Preliminary observations indicate the presence of a region outside th e catabolic genes downstream of bphA4 which is involved in mediating a t least the basal expression of BphC.