Organisation 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-chlorobenzo-ate derivatives. We constructed a cosmid library of Tn4371 DNA. The bph genes involved in biphenyl/4-chlorobiphenyl degradation were found to be clustered in the middle of the transposon. Sequencing revealed an organisation of the bph genes similar to that previously found in Pseudomonas sp. KKS102, i.e. the bphEGF genes are located upstream of bphA1A2A3 and bphA4 is separated from bphA1A2A3 by bphBCD. Consensus sequences for σ54-associated RNA polymerase were found upstream of bphA1 and bphEGF. Plasmid RP4::Tn4371 was transferred into a mutant of Alcaligenes eutrophus H16 lacking σ54. In contrast to wild-type H16 exconjugants, the σ54 mutant exconjugants could not grow on biphenyl, indicating the dependence of Tn4371bph gene expression on σ54. 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 the catabolic genes downstream of bphA4 which is involved in mediating at least the basal expression of BphC.
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