Biphasic Chemotaxis of <i>E. coli</i> to the Microbiota Metabolite Indole

Bacterial chemotaxis to microbiota metabolites in the GI tract is important in the development of microbial communities. A prominent metabolite is indole, which has received wide attention for its role in regulating a broad range of bacterial phenotypes including virulence. The basis of chemotaxis to indole however, remains poorly understood. With a combination of flagellar motor and FRET assays, we have discovered a time-dependent inversion from a chemorepellent to chemoattractant response to indole. Such an inversion caused a bipartite response – wild-type cells were attracted to regions of high indole concentration if they had previously adapted to indole but were otherwise repelled. Interestingly, the flagellar motor itself mediated a repellent response independent of the chemoreceptors. I will discuss analytical models to explain these and other physiological responses to indole. The spatial filtering of cells by indole is likely important in repelling invaders while recruiting beneficial resident bacteria to growing microbial communities within the GI tract.