Antunes Research Project Summary

The human body is colonized by a complex microbial community with critical roles for health. This microbiota educates the immune system, helps digest our food, and protects us against pathogens. The diversity of microbes and encoded functions is significant. Our group showed that the gut microbiota is also a source of great chemical diversity, and that most of the compounds produced are unknown. Bacteria produce and respond to small molecules to communicate and adapt to their environment. Chemical signaling controls functions that are critical for host adaptation in most pathogens. Therefore, small-molecule signaling is an attractive target for the development of anti-infectives. Given the chemical complexity of the gut, microbiotapathogen crosstalk must be common. In fact, we previously showed that an organic extract of human feces elicits a significant transcriptional response in Salmonella enterica, with ~100 regulated genes. Interestingly, virulence genes were abundant among those repressed by the extract, suggesting that microbiota-derived metabolites can dampen virulence. We then determined that a single commensal, Enterocloster citroniae, can repress S. enterica virulence gene expression. More recently, we studied the transcriptional impact of the human fecal metabolome on other pathogens. In Vibrio cholerae, the causative agent of cholera, the effect was even more pronounced, with ~900 genes being regulated. Motility was the main category of repressed genes, and the effect was confirmed by phenotypic assays. As with S. enterica, the effect could be recapitulated with E. citroniae. Given the importance of V. cholerae as a human pathogen and the critical role played by motility in its pathogenesis, it is our goal to determine the impact of microbiota-derived metabolites on V. cholerae pathogenicity. We will generate a collection of gut commensals with anti-motility properties to characterize the genetic and chemical nature of the bioactivity. Genomes and transcriptomes of active and inactive strains will be compared, giving insights into the synthetic apparatus involved. Bioactivity-guided purification will be performed, and compound characterization using mass spectrometry and nuclear magnetic resonance will ensue. Lastly, we will study the impact of active strains and compounds on host resistance to V. cholerae using infection models. Results from this work will shed light on the chemical biology of microbiota-pathogen interactions and may reveal strains and compounds with potential therapeutic applications.