Random Walks, Hydrodynamic Interactions, and Molecular Memory in Bacteria

Pushkar Lele from Texas A&M University
Melcher Hall rm 170

Brownian motion limits the amount of control bacteria have over their movements. To improve the odds of reaching a nutrient source, bacteria have evolved an elegant intracellular signaling network – the chemotaxis network – and a motility apparatus – the flagellum. Together, they enable the cell to make temporal comparisons of chemical signal levels and to bias it’s random walk in response. To successfully migrate in a preferred direction, the bug needs a short-time memory of the current signal levels. I will present our recent discovery with the gut-dwelling E. coli that demonstrates a novel function for this memory. With the aid of in vivo single motor biophysical assays, Förster resonance energy transfer, microfluidics, and genetic engineering, we have found that chemotactic memory induces a biphasic response to indole, an important gastrointestinal tract metabolite. When indole levels are high, E. coli seems to love it’s taste. When indole levels are low, E. coli would rather avoid it. I will speculate on how such metabolites might help maintain healthy gut microenvironments while resisting pathogens. In contrast, our measurements of hydrodynamic interactions of individual Helicobacter pylori cells with no-slip boundaries together with the time reversibility of Stokes flows indicate that this memory may not be relevant for H. pylori-chemotaxis. How do H. pylori cells ever find their way?