Variation in chemotactic strategies within and across bacterial species

AbstractBacteria use a conserved signaling pathway to direct their behavior in chemical gradients. This directed motioncalled chemotaxis is essential for clinically relevant phenomena like biofilm formation and host invasion.Extensive work has characterized the dynamics of chemical sensing adaptation and behavior in Escherichiacoli. However a fully integrated picture of chemotaxis is currently lacking in other bacteria. Given the diversity ofsensing and behavioral strategies across bacteria to fully understand the role of chemotaxis in pathogenicity itis essential to characterize the interaction between signal transduction and behavior in other species.In this application the PI proposes to extend two experimental lines of inquiry first explored in E. coli topathogenic bacteria. One direction of the lab is to use single-cell fluorescence resonance energy transfer tocharacterize the dynamics of chemotactic signal processing to Vibrio cholerae. While E. coli navigate with run-and-tumble cycles alternating between straight runs and stationary reorienting tumbles V. cholerae and othersingly-flagellated bacteria navigate with run-reverse-flick cycles where after a run cells backtrack along theirrun trajectory and then flick at a 90o angle. In a chemical gradient different swimming behaviors will generateinputs to the chemosensory system with different statistics. Characterizing chemosensory responses in V.cholerae will reveal how a common signaling architecture can be repurposed to process diverse signals andcontrol diverse chemotaxis strategies.Another direction of the lab is to study the role of cell-to-cell variability in chemotactic behavior and its effect onthe collective migration of populations. By consuming environmental attractants groups of bacteria can establishmoving attractant gradients to follow which results into waves or bands of migrating bacteria that can travel overlong distances. For E. coli our lab previously demonstrated that during collective migration individual phenotypesspontaneously sort themselves along the traveling gradient according to their chemotactic performance.Importantly we found that the leader-follower organization that emerges enables traveling populations to overtime adapt their phenotypic composition to the environments they traverse by culling the weakest phenotypesthat end up at the back of the traveling group. Moving forward we want to understand the dynamics of how newspatial configurations of chemotaxis phenotypes emerge when populations encounter new environments andthe consequences of spatial sorting in migrating populations on pathogenicity. As such we will examinephenotypic diversity in traveling waves of E. coli migrating through interfaces between liquid and agar and ofPseudomonas aeruginosa were virulence traits and chemotaxis are often coregulated.