Interplay between chemotaxis, quorum sensing, and metabolism regulates Escherichia coli-Salmonella Typhimurium interactions in vivo

Motile bacteria use chemotaxis to navigate complex environments like the mammalian gut. These bacteria sense a range of chemoeffector molecules, which can either be of nutritional value or provide a cue for the niche best suited for their survival and growth. One such cue molecule is the intra- and interspecies quorum sensing signaling molecule, autoinducer-2 (AI-2). Apart from controlling collective behavior of Escherichia coli, chemotaxis towards AI-2 contributes to its ability to colonize the murine gut. However, the impact of AI-2-dependent niche occupation by E. coli on interspecies interactions in vivo is not fully understood. Here, using the C57BL/6J mouse infection model, we show that chemotaxis towards AI-2 contributes to nutrient competition and thereby affects colonization resistance conferred by E. coli against the enteric pathogen Salmonella enterica serovar Typhimurium (S. Tm). Like E. coli, S. Tm also relies on chemotaxis, albeit not towards AI-2, to compete against residing E. coli in a gut inflammation-dependent manner. Finally, by using a barcoded mutant library pool of S. Tm, we analyzed how AI-2 signaling in E. coli affects the central metabolism of S. Tm. AI-2-dependent niche colonization by E. coli specifically affected the fitness of S. Tm mutants deficient in fumarate respiration ({Delta}dcuABC) or mannose ({Delta}manA) utilization. Our findings thus provide important insights into AI-2-mediated E. coli-S. Tm interactions during gut infection. Author SummaryBoth chemotaxis and AI-2 quorum sensing systems have been extensively studied in Escherichia coli. Despite our understanding of these systems at a molecular level in vitro, their physiological relevance in vivo, particularly in the context of mammalian gut colonization, remains less explored. Building on our previous work on the role of chemotaxis and AI-2 signaling in E. coli gut colonization, we investigated their roles in interspecies interactions. Specifically, we examined how AI-2-dependent colonization by E. coli affects its competition with the enteric pathogen Salmonella enterica serovar Typhimurium (S. Tm) and the metabolic requirements for S. Tm growth. Our data show that AI-2 signaling contributes to colonization resistance of E. coli against S. Tm. Although S. Tm also requires chemotaxis to grow efficiently in E. coli-colonized mice, this is independent of its ability to sense AI-2. Notably, AI-2-dependent niche occupation by E. coli altered S. Tm metabolism at different stages of infection. Collectively, our findings highlight how AI-2 signaling in one species can affect the metabolism of its interaction partners in vivo.