Infection with novel Bacteroides phage BV01 alters host transcriptome and bile acid metabolism in a common human gut microbe

The bacterial genus Bacteroides is among the most abundant and common taxa in the human gut, yet little is known about the phages infecting the group. Bacteroides phage BV01 (BV01) was identified as a prophage integrated on the chromosome of its host, Bacteroides vulgatus ATCC 8482. Phage BV01 is actively produced, and infects susceptible B. vulgatus hosts in the mouse gut. Infection with BV01 causes a generalized repression of the B. vulgatus transcriptome, downregulating 103 transcripts and upregulating only 12. Integration of BV01 disrupts the promoter sequence of a downstream gene encoding a putative tryptophan-rich sensory protein ( tspO ). Deletion of tspO and subsequent RNAseq analysis revealed that more than half of the differentially-regulated transcripts are shared with the BV01 lysogen, suggesting the transcriptomic response to BV01 is linked to tspO . Among these differentially-regulated transcripts are two encoding bile salt hydrolases. Bile acid deconjugation assays show that BV01 represses its host’s ability to hydrolyze bile acids in a tspO -dependent manner. Analysis of 256 published healthy human gut metagenomes suggests that phage integration adjacent to B. vulgatus -like tspO genes is rare within an individual, but common among humans. Finally, this work proposes a novel phage family that includes BV01, the Salyersviridae , whose host range spans the Bacteroides and is detectable in human-associated samples. Together, these findings highlight the importance of phage-host interactions to our understanding of how gut microbes sense and interact with their environment. IMPORTANCE The links between human disease and the gut microbiome are numerous. Most mechanisms by which most gut microbes and their activities change and impact human health remain elusive. Phages, viruses that infect bacteria, are hypothesized to play a central role in modulating both community dynamics and functional activities. Here we have characterized an active prophage, BV01, which infects a pervasive and abundant human gut-associated species. BV01 infection alters its host’s transcriptional profile including its metabolism of bile acids, molecules implicated in mediating health and disease states in the gut. This highlights that prophages and other components of the variable genome should not be overlooked in bacterial genomes because they may dramatically alter host phenotypes. Furthermore, BV01 represents a new family of phages infecting human gut symbionts, providing a foundation for future investigations of phage-host interactions in these clinically-relevant but underexplored hosts.