(188dn) Investigating Signal Integration in Bacteria Chemotaxis

The mammalian gastrointestinal (GI) tract harbors a diverse community of microbes, collectively known as the microbiota. The metabolites produced by the microbial community during its growth and sustenance have been postulated to be important determinant of health and disease. Previous work from our lab identified that the microbiota metabolizes host-produced norepinephrine to dihydroxymandelic acid (DHMA), which is a potent chemoattractant and inducer of virulence for enterohemorrhagic E. coli (EHEC). We have also previously shown that the microbial metabolite indole produced from tryptophan attenuates EHEC chemotaxis and virulence. While individual effects of different metabolites are well established, the interaction between different metabolites and their integrated effect on EHEC chemotaxis and virulence is poorly understood. The overall goal of this study is to investigate the interaction between DHMA and indole in modulating chemotaxis in EHEC. Using non-pathogenic E. coli as a model, we investigated the effect of indole and DHMA on the flagellar motor as well as on chemotactic migration. First, cells were tethered to a glass slide and exposed to different concentrations of the two signals while recording the rotation of the bidirectional bacterial flagellar motor. The pre-stimulus and post-stimulus clockwise bias, which is the probability of CW rotation of the motor, was simultaneously measured to determine the effects on chemotactic signaling. Indole elicited a pronounced increase in the CW bias, indicating a strong repellent response, whereas exposure to DHMA decreased the CW bias (i.e, an attractant response) in a dose-dependent manner. Additionally, we also investigated the chemoreceptor(s) involved in the repellent response to indole. Mutants lacking the tsr and tar chemoreceptors remained sensitive to indole, suggesting that the repellent response to indole is not mediated by either receptor, contrary to earlier reports. Instead, we will discuss a potential mechanism by which the response to indole might be mediated. Finally, we will discuss the measurements of the effects of indole on chemotactic migration in a flow-based microfluidic assay and its correlation with the motor measurements.