A GntR-like negative regulator of the biphenyl degradation genes of the transposon Tn4371

Abstract

Tn4371, a 55-kb catabolic transposon originally isolated from Ralstonia eutropha A5, carries genes for the degradation of biphenyl/4-chlorobiphenyl, which are clustered on a 13-kb DNA segment located in the middle of the element. DNA sequencing revealed that two potential regulatory genes, bphR and bphS, border this region. Transcriptional fusion experiments using bphC as a reporter gene, Northern hybridization and primer extension analysis led to the conclusion that the transposon-encoded genes bphEFGA1A2A3BCD form an operon transcribed from a sigma70 promoter, pE. Transcription from pE was not influenced by deletion of the bphR gene of Tn4371, which should encode a LysR-like regulator. The bphS gene product negatively regulated pE, and displayed significant similarity to GntR-like regulators. This is the first reported example of a GntR-like regulator involved in the control of an aromatic degradation pathway.

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).…”

“…The GntR-type regulatory proteins involved in the degradation of aromatic compounds are also reported to be repressors (18,31). However, ORF0 in KF707 is not likely to be a repressor (silencer) but more likely to be an activator being required for the expression of the lower pathway genes of bphX0X1X2X3D (Figs.…”

“…These results allowed us to conclude that the orf0 is transcribed alone but not co-transcribed with other degradative genes. The bphS and aphS regulatory genes are independently transcribed with respect to their degradative genes (18,31). On the other hand, the gntR gene in the gnt operon of B. subtilis is inducibly co-transcribed with the other genes.…”

“…Recently, it was suggested that the bph gene cluster in Tn4371 found from Ralstonia eutropha A5, bphEFGA1A2A3BCD, forms an operon transcribed from a 70 promoter and that the bphS gene product negatively regulates the transcription of the bph gene cluster as a repressor (18). On the other hand, the bph operon in Gram-positive Rhodococcus sp.…”

Ralstonia metallidurans CH34 RpoN sigma factor and the control of nitrogen metabolism and biphenyl utilization The GenBank accession number for the sequence determined in this work is AJ131690.

“…In R. metallidurans CH34, most Tn4371 bph genes are however transcribed from a single σ(! promoter (Mouz et al, 1999).…”