Microcolony morphology drives bacterial responses in complex environments

Individual bacterial cells adopt a wide range of shapes whose physiological functions have been extensively studied. Bacterial microcolonies also adopt characteristic shapes like clusters and chains that vary significantly even between species with similar single-cell shapes. Despite their ubiquity, the functions of bacterial microcolony morphologies remain largely unknown. Here I provide evidence that microcolony morphology is a major determinant of bacterial colonization in flow. Clinical reports of heart infections present a surprising paradox: bacteria like S. aureus and E. faecalis preferentially colonize areas of high fluid flow. Utilizing microfluidic devices and computational models, I explored the dynamics of how these two species respond to flow. I discovered distinct mechanisms used by the two species to colonize in high fluid flow, and both act at the microcolony scale. S. aureus grows in a clustered morphology and transport of signaling molecules away from the clustered cells disrupts dispersal signaling. Conversely, E. faecalis grows in linear chains and mechanical forces from flow push cells towards the surface, leading to more cells attached in higher fluid flow. Overall, this work elucidates two distinct mechanisms by which bacterial microcolony morphologies drive colonization behaviors and introduces a new perspective to consider when exploring bacterial behaviors in complex environments.