Affiliation:
1. Department of Microbiology and Immunology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia 23298
Abstract
ABSTRACT
Clostridium
sp. strain TO-931 can rapidly convert the primary bile acid cholic acid to a potentially toxic compound, deoxycholic acid. Mixed oligonucleotide probes were used to isolate a gene fragment encoding a putative bile acid transporter from
Clostridium
sp. strain TO-931. This DNA fragment had 60% nucleotide sequence identity to a known bile acid transporter gene from
Eubacterium
sp. strain VPI 12708, another bile acid-7α-dehydroxylating intestinal bacterium. The DNA (9.15 kb) surrounding the transporter gene was cloned from
Clostridium
sp. strain TO-931 and sequenced. Within this larger DNA fragment was a 7.9-kb region, containing six successive open reading frames (ORFs), that was encoded by a single 8.1-kb transcript, as determined by Northern blot analysis. The gene arrangement and DNA sequence of the
Clostridium
sp. strain TO-931 operon are similar to those of a
Eubacterium
sp. strain VPI 12708 bile acid-inducible operon containing nine ORFs. Several genes in the
Eubacterium
sp. strain VPI 12708 operon have been shown to encode products required for bile acid 7α-dehydroxylation. In
Clostridium
sp. strain TO-931, genes potentially encoding bile acid-coenzyme A (CoA) ligase, 3α-hydroxysteroid dehydrogenase, bile acid 7α-dehydratase, bile acid-CoA hydrolase, and a bile acid transporter were similar in size and exhibited amino acid homology to similar gene products from
Eubacterium
sp. strain VPI 12708 (encoded by
baiB
,
baiA
,
baiE
,
baiF
, and
baiG
, respectively). However, no genes similar to
Eubacterium
sp. strain VPI 12708
biaH
or
baiI
were found in the
Clostridium
sp. strain TO-931
bai
operon, and the two putative
Eubacterium
sp. strain VPI 12708 genes,
baiC
and
baiD
, were arranged in one continuous ORF in
Clostridium
sp. strain TO-931. Intergene regions showed no significant DNA sequence similarity, but primer extension analysis identified a region 115 bp upstream from the first ORF that exhibited 58% identity to a
bai
operator/promoter region identified in
Eubacterium
sp. strain VPI 12708. These results indicate that the gene organization, gene product amino acid sequences, and promoters of the bile acid-inducible operons of
Clostridium
sp. strain TO-931 and
Eubacterium
sp. strain VPI 12708 are highly conserved.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
126 articles.
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