Chemotaxis of Pseudomonas aeruginosa : the control of chemotaxis by nitrogen and the role of methionine in chemotaxis

Date Issued
December 1, 1981
Author(s)
Craven, Rebecca Carol
Advisor(s)
T. C. Montie
Additional Advisor(s)
Raymond Beck
Jeffrey Becker
Leaf Huang
Permanent URI
Abstract
The regulation of amino acid chemotaxis by nitrogen and the role of protein methylation in chemotaxis of the gram-negative bacterium Pseudomonas aeruginosa were investigated. The quantitative capillary tube technique was used to measure chemotactic responses of bacteria to spatial gradients of amino acids and other attractants. Chemotaxis toward serine, arginine, and &alpha-aminoisobutyrate (AIB) was sharply dependent on the form in which nitrogen was presented to the bacteria. Bacteria grown on mineral salts-succinate (MMS) with potassium nitrate gave responses to amino acids that were 2 to 3 times those of cells grown on ammonium sulfate and 10 to 20 times those of cells grown in MSS with casamino acids (CAA) as the nitrogen source. A combination of ammonium sulfate and glutamate was as effective as CAA in depressing serine taxis. The threshold concentration for AIB taxis was consistently lower in nitrate-grown bacteria than in ammonia-grown bacteria. Responsiveness to sodium succinate, however, was not subject to regulation by nitrogen, and glucose chemotaxis chemotaxis was inhibited, rather than enhanced, in nitrate-grown bacteria. These results indicate that chemotaxis of P. Aeruginosa toward amino acids is subject to regulation by nitrogen and that this regulation probably occurs at the level of the chemoreceptors or transducers.

P. aeruginosa was further examined for the presence of a chemotaxis-associated methyl transfer reaction. The cells were labeled with [methyl- H]-methionine in the presence of chloramphenicol and then stimulated with chemoattractants. Labeled components were analyzed by iii IV fluorography of sodium dodecyl sulfate-polyacrylamide electrophoretic gels. Two bands of approximately 73,000 daltons were methylated in response to stimulation by arginine, serine or AIB. The strength of the methylation response corresponded to the strength of the chemotactic stimulus. The level of methylation decreased in response to attractant 35 dilution. The results of labeling of whole cells with [35S]methionine 3 and in vitro labeling with S-adenosyl-[methyl- 3H] methionine indicated that the 73,000 dalton band is labeled by a methyl transfer reaction. This methylated species, therefore, appears to be analogous to the methyl-accepting chemotaxis proteins (MCP) of the enteric bacteria.

Degree
Doctor of Philosophy
Major
Microbiology
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