| Chemotaxis, the ability of motile bacteria to detect and respond to specific chemicals in the environment, can help bacteria find an optimal niche for their survival and growth. This dissertation describes chemotactic responses to two groups of structurally related compounds, s-triazines and pyrimidines, in Escherichia coli and Pseudomonas species.;E. coli was chemotactically attracted to the pyrimidines thymine and uracil, as well as the s-triazine compounds N-isopropylammelide and cyanuric acid. E. coli mutants lacking the methyl-accepting chemotaxis protein (MCP) Tap lost the ability to respond to both pyrimidines and s-triazines. These data indicate that pyrimidines and triazines are detected by the same chemoreceptor (Tap) in E. coli . Pyrimidines are the closest naturally-occurring structures to triazines. Because E. coli uses pyrimidines but not s-triazines as sole sources of nitrogen, we propose that chemotaxis towards s -triazines is due to fortuitous recognition by the pyrimidine chemoreceptor in E. coli.;Pseudomonas sp. strain ADP utilizes the man-made s-triazine herbicide atrazine as sole nitrogen source. This strain was attracted to the s-triazines atrazine, hydroxyatrazine, N-isopropylammelide and cyanuric acid. The response was not induced during growth with atrazine, and atrazine metabolism was not required for the chemotactic response. Strain ADP, as well as Pseudomonas putida strains F1 and PRS2000, responded to cytosine, but did not respond or responded very weakly to thymine and uracil. McpC, a newly identified MCP gene, was demonstrated to encode the cytosine chemoreceptor in strain F1. P. putida strains F1 and PRS2000 also responded to s-triazines, and McpC is involved in chemotaxis responses towards N-isopropylammelide in F1.;In addition to the characterization of s-triazine and pyrimidine chemotaxis, this work analyzed the putative MCPs in P. putida F1 and uncovered specific chemotaxis and aerotaxis functions for several MCPs. |
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