Bacterial chemotaxis is a paradigm for how environmental signals modulate behavior. Escherichia coli, like many species of bacteria, swim by rotating a bundle of helical flagella driven by bi-directional rotary motors. Cells swim in a random pattern described as a series of swims along an approximately straight path called “runs” interrupted by abrupt changes in direction called “tumbles”. This simple picture of cell motility is an idealization of a more complex dynamical problem, in which multiple flagella collectively determine whether cell swimming behavior. Despite extensive studies on the network underlying this process, the relationship between cell swimming state and flagellar state remains poorly characterized. Quantifying this relationship remains a missing link to an end-to-end understanding of bacterial chemotaxis. In this talk, I will discuss new approaches we have developed that allow us to measure the swimming behavior of individual cells while simultaneously detecting the rotational states of each flagellum. A simple mapping relating the cell’s swimming state to the number and average rotational state of its flagella emerges. An important aspect of our findings is that the cell’s swimming behavior appears “robust” against variations in number of flagella, a property that may confer advantages to the cell population. Time permitting, I will also discuss new work on the quantitative analysis of swimming behavior in a higher organism, the vertebrate zebrafish.
Lunch @ 11:45, talk @ 12pm.