Richard C. Stewart

Associate Professor

Research Interests: Signal transduction in microorganisms.

Teaching Interests: Microbial physiology; Microbialgenetics; Introductory microbiology

Microbes live life on the edge: they have little or no ability to change their environments, and they face fierce competition for limited resources.  So it is not surprising that microorganisms are jam-packed with fascinating sensory-response systems that enable them to respond quickly and appropriately when their environments change.  For example, many bacteria can control their swimming movements in ways that lead them toward more favorable environments: toward food sources;  toward surfaces amebable for colonization; away from harmful chemicals.  Controlling cell movements in response to gradients of chemicals is called chemotaxis, and in my laboratory we are investigating how a small set of signal-transducing proteins (CheA, CheW, CheY, CheZ, CheR, CheB, and receptors) interact to allow E. coli to respond, with exquisite sensitivity, to gradients of amino acids, sugars, and oxygen.  The responses mediated by the chemotaxis system are not simple 'knee-jerk' responses, but rather involve the cell making comparisons of the current environment to the environment it experienced a few seconds ago.   This is a remarkably sophisticated abilitiy for a 'simple bacterium', especially when you realize that it makes these comparisons on a very rapid (sub-second) time scale!  Our long term goal is to understand, at a molecular level, how the combined activities of the Che proteins generate this sophisticated regulation of swimming behavior.  Current research activities in my laboratory focus on defining how the activity of the protein kinase (CheA) in this system is controlled by the cell-surface receptors responsible for detecting local amino acid and sugar concentrations. 

Selected Recent Publications:

Boukhvalova, M.S., Dahlquist, F.W., and Stewart, R.C. 2002. CheW binding interactions with CheA and Tar: Importance for chemotaxis signaling in Escherichia coli. J. Biological Chemistry 277, 22251-22259.

Boukhvalova, M.S., VanBruggen, R., and Stewart, R.C. 2002. CheA kinase and chemoreceptor interaction surfaces on CheW. J. Biological Chemistry 277, 23596-23603.

Hirschman, A., Boukhvalova, M.S., VanBruggen, R., Wolfe, A.J., and Stewart, R.C. 2001. Active site mutations in CheA, the signal-transducing protein kinase of the chemotaxis system in Escherichia coli. Biochemistry 40, 13876-13887.