| Ralstonia sp. strain U2 and Pseudomonas putida G7 are capable of completely mineralizing the environmental pollutant naphthalene. The naphthalene degradation pathways in these two organisms have been well characterized. Less is known about how strains U2 and G7 use chemotaxis, which is the movement of motile cells toward or away from an environmental chemical, to detect naphthalene. This dissertation describes the chemotactic responses of strains U2 and G7 to naphthalene and related compounds.;Ralstonia sp. strain U2 was chemotactically attracted to naphthalene, but not to the naphthalene degradation intermediates salicylate or gentisate. The response to naphthalene by strain U2 was induced by growth with naphthalene, salicylate, or gentisate, suggesting that the response is under regulatory control. Interestingly, NagR, the regulator of the naphthalene catabolic genes in strain U2, did not regulate naphthalene chemotaxis. Assays with a plasmid-cured derivative of strain U2 indicated that the gene(s) responsible for naphthalene chemotaxis in strain U2 were located on the same catabolic plasmid as the naphthalene degradation genes. The putative methyl-accepting chemotaxis protein (MCP), NagY, which is encoded upstream of the naphthalene degradation genes, was hypothesized to mediate naphthalene chemotaxis in strain U2, but was not required for the response. We looked for new chemotaxis gene candidates by employing a whole-genome mutagenesis strategy, but did not find any naphthalene chemotaxis mutants. Finally, strain U2 was shown to be chemotactic to four other aromatic hydrocarbon attractants in addition to naphthalene.;We confirmed previously published results stating that P. putida G7 was chemotactically attracted to naphthalene, while the naphthalene chemotaxis mutant G7Y1 (lacking nahY) was not. The nahY gene complemented naphthalene chemotaxis defects in several G7 derivative strains, and conferred the ability to respond to naphthalene on P. putida PRS2000. Complementation of the same G7 derivatives and strain PRS2000 with nahXY resulted in an apparently stronger response to naphthalene, suggesting that NahX may play a role in strain G7 naphthalene chemotaxis that has not been previously described. It was also determined that strain G7 has two distinct chemoreceptors for naphthalene and salicylate, and that the naphthalene chemoreceptor NahY can also mediate chemotaxis to the aromatic hydrocarbon biphenyl in addition to naphthalene. |
