Ramachandran, A.; Stone, H. A.; Gitai, Z.

Planktonic (free-floating) cells are typically assumed to be oblivious to any flow that carries them. Here we discover that planktonic bacteria can sense flow to induce gene expression changes that are beneficial in flow. Specifically, planktonic P. aeruginosa induce shear-rate-dependent genes that promote growth in low oxygen environments. Untangling this mechanism revealed that in flow, motile P. aeruginosa spatially redistribute, leading to cell density changes that activate quorum sensing, which in turn enhances oxygen uptake rate. In diffusion-limited environments, including those commonly encountered by bacteria, flow-induced cell density gradients also independently generate oxygen gradients that alter gene expression. Mutants deficient in this newly-discovered flow sensing mechanism exhibit decreased fitness in flow, suggesting that this dynamic coupling of biological and mechanical processes can be physiologically significant.