Swim/stick tradeoffs for gut bacterial symbionts*

For microorganisms motility is primarily a dispersal mechanism, enabling them to find new environments at an energetic cost, and yet it is widespread in species of symbiotic bacteria that have adapted to long-term residence in the intestine. Deciphering the costs and benefits of gut bacterial motility will inform our understanding of the ecology and biophysics of the intestinal microbiome, specifically the interplay between the spatial structures of the host environment and its bacterial communities. I’ll present work that investigates these issues by using light sheet microscopy to observe native and genetically perturbed bacterial communities in the intestines of live, larval zebrafish. Our findings reveal a novel benefit of motility: when directed towards an upstream chemotactic cue, motility is extremely effective at countering downstream peristaltic transport. However, the benefits of motility are fragile: small chemical perturbations that impede motility lead to massive population losses via peristaltic transport out of the gut. Together, these results offer insight into how bacterial motility dictates population-scale spatial structure and dynamics in the intestine.