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Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271.

ABSTRACT: Primary bile acids are synthesized from cholesterol in the liver, conjugated to either glycine or taurine and secreted into bile. Bile salts undergo enterohepatic circulation several times each day. During this process, they are biotransformed into a variety of metabolites by gut bacteria. The major biotransformation is the 7alpha-dehydroxylation of cholic acid and chenodeoxycholic acid yielding deoxycholic acid and lithocholic acid, respectively. 7alpha-Dehydroxylation is a multi-step pathway. The genes encoding enzymes in this pathway have been identified in two species of "high" activity strains of clostridia. Here, we report the isolation and characterization of a bile acid inducible (bai) operon in Clostridium hylemonae, a "low" activity 7alpha-dehydroxylating strain. The gene organization and sequence of the baiBCDEFGHI operon was highly conserved between C. hylemonae and "high" activity strains. Surprisingly, the baiA gene was missing from the bai operon of C. hylemonae. The baiA gene was isolated using PCR and degenerate oligonucleotide primers. The mRNA start site for the large bai operon was determined and shown to be only 11bp from the initiation codon of the first gene. It was also discovered that allocholic acid (5alpha) induced the bai operon and stimulated the conversion of [24-(14)C] cholic acid to [24-(14)C] allodeoxycholic acid in cultures of C. scindens and C. hylemonae allodeoxycholic acid. Finally, it was discovered that the addition of testosterone to the growth medium markedly increased 7alpha-dehydroxylation of cholic acid in Clostridium scindens and C. hylemonae. We hypothesize that testosterone may be a gratuitous inducer of genes involved in the reductive arm of the bile acid 7alpha-dehydroxylation pathway.

SUBMITTER: Ridlon JM

PROVIDER: S-EPMC6262846 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

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Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271.

Ridlon Jason M JM Kang Dae-Joong DJ Hylemon Phillip B PB

Anaerobe 20090521 2

Primary bile acids are synthesized from cholesterol in the liver, conjugated to either glycine or taurine and secreted into bile. Bile salts undergo enterohepatic circulation several times each day. During this process, they are biotransformed into a variety of metabolites by gut bacteria. The major biotransformation is the 7alpha-dehydroxylation of cholic acid and chenodeoxycholic acid yielding deoxycholic acid and lithocholic acid, respectively. 7alpha-Dehydroxylation is a multi-step pathway. ...[more]

PMID: 19464381

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Project description: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-7alpha-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 7alpha-dehydroxylation. In Clostridium sp. strain TO-931, genes potentially encoding bile acid-coenzyme A (CoA) ligase, 3alpha-hydroxysteroid dehydrogenase, bile acid 7alpha-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.

Project description:Bile acids are important cholesterol-derived nutrient signaling hormones, synthesized in the liver, that act as detergents to solubilize dietary lipids. Bile acid 7?-dehydroxylating gut bacteria generate the toxic bile acids deoxycholic acid and lithocholic acid from host bile acids. The ability of these bacteria to remove the 7-hydroxyl group is partially dependent on 7?-hydroxysteroid dehydrogenase (HSDH) activity, which reduces 7-oxo-bile acids generated by other gut bacteria. 3?-HSDH has an important enzymatic activity in the bile acid 7?-dehydroxylation pathway. 12?-HSDH activity has been reported for the low-activity bile acid 7?-dehydroxylating bacterium Clostridium leptum; however, this activity has not been reported for high-activity bile acid 7?-dehydroxylating bacteria, such as Clostridium scindens, Clostridium hylemonae, and Clostridium hiranonis Here, we demonstrate that these strains express bile acid 12?-HSDH. The recombinant enzymes were characterized from each species and shown to preferentially reduce 12-oxolithocholic acid to deoxycholic acid, with low activity against 12-oxochenodeoxycholic acid and reduced activity when bile acids were conjugated to taurine or glycine. Phylogenetic analysis suggests that 12?-HSDH is widespread among Firmicutes, Actinobacteria in the Coriobacteriaceae family, and human gut ArchaeaIMPORTANCE 12?-HSDH activity has been established in the medically important bile acid 7?-dehydroxylating bacteria C. scindens, C. hiranonis, and C. hylemonae Experiments with recombinant 12?-HSDHs from these strains are consistent with culture-based experiments that show a robust preference for 12-oxolithocholic acid over 12-oxochenodeoxycholic acid. Phylogenetic analysis identified novel members of the gut microbiome encoding 12?-HSDH. Future reengineering of 12?-HSDH enzymes to preferentially oxidize cholic acid may provide a means to industrially produce the therapeutic bile acid ursodeoxycholic acid. In addition, a cholic acid-specific 12?-HSDH expressed in the gut may be useful for the reduction in deoxycholic acid concentration, a bile acid implicated in cancers of the gastrointestinal (GI) tract.

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Project description:The formation of secondary bile acids by gut microbes is a current topic of considerable biomedical interest. However, a detailed understanding of the biology of anaerobic bacteria in the genus Clostridium that are capable of generating secondary bile acids is lacking. We therefore sought to determine the transcriptional responses of two prominent secondary bile acid producing bacteria, Clostridium hylemonae and Clostridium hiranonis to bile salts (in vitro) and the cecal environment of gnotobiotic mice. The genomes of C. hylemonae DSM 15053 and C. hiranonis DSM 13275 were closed, and found to encode 3,647 genes (3,584 protein-coding) and 2,363 predicted genes (of which 2,239 are protein-coding), respectively, and 1,035 orthologs were shared between C. hylemonae and C. hiranonis. RNA-Seq analysis was performed in growth medium alone, and in the presence of cholic acid (CA) and deoxycholic acid (DCA). Growth with CA resulted in differential expression (>0.58 log2FC; FDR < 0.05) of 197 genes in C. hiranonis and 118 genes in C. hylemonae. The bile acid-inducible operons (bai) from each organism were highly upregulated in the presence of CA but not DCA. We then colonized germ-free mice with human gut bacterial isolates capable of metabolizing taurine-conjugated bile acids. This consortium included bile salt hydrolase-expressing Bacteroides uniformis ATCC 8492, Bacteroides vulgatus ATCC 8482, Parabacteroides distasonis DSM 20701, as well as taurine-respiring Bilophila wadsworthia DSM 11045, and deoxycholic/lithocholic acid generating Clostridium hylemonae DSM 15053 and Clostridium hiranonis DSM 13275. Butyrate and iso-bile acid-forming Blautia producta ATCC 27340 was also included. The Bacteroidetes made up 84.71% of 16S rDNA cecal reads, B. wadsworthia, constituted 14.7%, and the clostridia made up <.75% of 16S rDNA cecal reads. Bile acid metabolomics of the cecum, serum, and liver indicate that the synthetic community were capable of functional bile salt deconjugation, oxidation/isomerization, and 7α-dehydroxylation of bile acids. Cecal metatranscriptome analysis revealed expression of genes involved in metabolism of taurine-conjugated bile acids. The in vivo transcriptomes of C. hylemonae and C. hiranonis suggest fermentation of simple sugars and utilization of amino acids glycine and proline as electron acceptors. Genes predicted to be involved in trimethylamine (TMA) formation were also expressed.

Dataset Information

Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271.

Publications

Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271.

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