Identifying a Novel Bile Salt Hydrolase from the Keystone Gut Bacterium Christensenella minuta.

Guillaume Déjean,Lisa Bruno,Déborah Kissi,Héloïse Tudela,Sandrine P Claus,Georges Rawadi

doi:10.3390/microorganisms9061252

Abstract

Christensenella minuta are human gut dwelling bacteria that have been proposed as key members of the gut microbiome, regulating energy balance and adiposity of their host. We formerly identified that a novel strain of C. minuta (strain DSM33407) boosted microbiota diversity and stimulated deconjugation of the primary bile acid taurocholic acid in human samples. However, there is no description of a bile salt hydrolase (BSH) protein carried in the genome of C. minuta. Here, we identified and cloned a protein from C. minuta’s genome that carries a potent BSH activity, which preferentially deconjugates glycine-conjugated bile acids. We then retrieved 14,319 putative BSH sequences from the NCBI database and filtered them using the UHGP database to collect a total of 6701 sequences that were used to build the most comprehensive phylogenetic tree of BSH-related enzymes identified in the human microbiome so far. This phylogenetic tree revealed that C. minuta’s BSH amino acid sequence clusters away from others with a threshold of 70% identity. This is therefore the first description of C. minuta’s BSH protein, which may be involved in its unique role within the human gut microbial ecosystem.

Highlights

The ability of C. minuta DSM22607 and DSM33407 to grow in the presence of bile acids was evaluated in 10 mL of modified GAM media broth (Hyserve, Uffing, Germany) supplemented with 0%, 2%, 4%, 6%, 8% w/v OxGall
We first evaluated the bile acid resistance potential of the novel strain CmDSM33407 and compared it to the type strain CmDSM22607. The growth of both strains was examined in modified GAM broth medium supplemented or not with a mixture of oxderived bile acids (i.e., OxGall powder) at increasing concentrations (Figure 1A,B). We observed that both strains were highly resistant to bile acids since they were still able to grow in the presence of 8% of OxGall, the equivalent of 80% of bile
Zooming again on the sub-cluster indicated by a bracket on Figure 6, we identified that C. minuta’s bile salt hydrolase (BSH) sequences are located within a specific cluster of Christensenellaceae sequences

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Christensenella minuta is a low abundance Gram-negative human gut commensal bacterial species of the Firmicutes phylum that has been suggested as a key modulator of adiposity [1,2]. It has been reported to consistently decrease in several human obese cohorts, suggesting that it carries a unique function associated with the regulation of energy metabolism [1,3–6]. Only one strain of C. minuta (DSM 22607, referred to further in the text as CmDSM22607) is available in culture collections, which is the original type strain described by Morotomi et al in 2012 [7]. In a recently published study, we demonstrated the anti-obesity potential of the novel strain Christensenella minuta DSM

Methods

Results

Discussion

Conclusion