Organisation of the bph gene cluster of transposon Tn4371, encoding enzymes for the degradation of biphenyl and 4-chlorobiphenyl compounds

Abstract

Tn4371 is a 55 kb transposon which encodes enzymes for the degradation of biphenyl and 4-chlorobiphenyl compounds into benzoate and 4-chlorobenzoate 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 sigma54-associated RNA polymerase were found upstream of bphA1 and bphEGF. Plasmid RP4::Tn4371 was transferred into a mutant of Alcaligenes eutrophus H16 lacking sigma54. In contrast to wild-type H16 exconjugants, the sigma54 mutant exconjugants could not grow on biphenyl, indicating the dependence of Tn4371 bph gene expression on sigma54. 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.

Versatile Transcription of Biphenyl Catabolic bphOperon in Pseudomonas pseudoalcaligenes KF707

“…Such elements permit microorganisms to degrade aromatic compounds by horizontal gene transfer. It was reported that the bph gene cluster involved in the metabolism of biphenyl/4-chlorobiphenyl is located in the 55-kb transposon Tn4371 (17,18,33,34). Our recent study also revealed that the 90-kb bph-sal element coding for biphenyl and salicylate metabolism behaves like a conjugative transposon in Pseudomonas putida KF715 whose bph gene cluster is nearly identical to that of KF707 except that the bphX0X1X2X3 genes were deleted (35).…”

Identification and Characterization of the Nitrobenzene Catabolic Plasmids pNB1 and pNB2 in Pseudomonas putida HS12

“…Many catabolic transposons which carry some part or all of the genes for the catabolism of aromatic compounds have been reported thus far. Tn4371 in Alcaligenes eutrophus A5 (22), Tn4651 and Tn4653 in plasmid TOL (39), Tn4655 in plasmid NAH7 (40), Tn5271 in plasmid pBRC60 (23), and Tn5707 in pENH91 (27) have been revealed to carry the catabolic genes for chlorobiphenyls, toluene, naphthalene, 3-chlorobenzoate, and chlorocatechol, respectively. It is presumed that the nbzB gene was transposed from an unknown source into a region of plasmid pNB2 by a Tn5501-like transposon.…”

A 90-Kilobase Conjugative Chromosomal Element Coding for Biphenyl and Salicylate Catabolism in Pseudomonas putida KF715

“…strain CB406 were mobilized following the construction in vivo of a cointegrate plasmid inserted into the broad-hostrange plasmid RP4 (22). Springael and coworkers (23,34) identified a transposon, Tn4371, carrying the bph genes encoding conversion of biphenyl to benzoic acid from Ralstonia eutrophus A5 (formerly Alcaligenes eutrophus A5) in which Tn4371 first transposed from the chromosome to indigenous IncP1 plasmid, and the plasmid carrying Tn4371 can be transferred to other strains by conjugation. A recent study shows that Tn4371 is a kind of conjugative transposon of 55 kb (24,29).…”