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Bacterial Chemotaxis
Research on chemotaxis in our laboratory focuses on the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. S. oneidensis is a facultative anaerobe that shows extreme respiratory versatility with respect to use of electron acceptors. Under anaerobic conditions these electron acceptors can be metals, e.g. Fe(III) or Mn(III/IV). In the environment, these metals are most likely to be present as insoluble minerals. Consequently, the question arises: How do metal-reducing bacteria locate minerals for respiratory purposes? We are attempting to answer this question by studying behavioral responses of S. oneidensis to metals.
S. oneidensis MR-1 has 3 clusters of chemotaxis genes that each appear to encode a chemotactic signal transduction pathway and 28 receptor genes that encode proteins similar to the methyl-accepting chemotaxis proteins. We have constructed mutants in many of the chemotaxis and receptor genes to identify specific mutant phenotypes. Using this approach, we have identified receptor proteins required for sensing both Fe(II) and Fe(III). We have also identified the signal transduction pathways that relay information from the receptors to the flagella motor. Interestingly, we have discovered that responses to Fe(II) and Fe(III) involve different receptor proteins and different signal transduction pathways. Specifically, responses to Fe(II) involve chemotactic behavior, while responses to Fe(III) involve energy taxis.
Currently, our research focuses on the following questions:
What is the mechanism of Fe(II) sensing in S. oneidensis?
Can behavioral responses to Fe(II) facilitate Fe(III)-mineral surface colonization?
What is the mechanism for respiratory electron transport sensing that facilitates responses to electron acceptors including Fe(III)?
Does S. oneidensis use energy taxis in the environment to locate the most energetically favorable locations for growth?
Are responses to toxic metals that can be used for anaerobic respiration (such as uranium and chromium) associated with energy sensing behavior?
Students interested in graduate studies in this area should contact Dr. Ward by e-mail.
Research Interests
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