A protein methylation reaction involved in chemotaxis of Escherichia coli has been identified. The involvement of this reaction in chemotaxis in indicated by four lines of evidence. (a) The methylation reaction is altered in several classes of generally nonchemotactic mutants and is coreverted with the chemotaxis defects. (b) The methylation level of the protein is affected by chemotactic stimuli. (c) The transferred methyl group is derived from methionine and is labile, in accord with the known fact that chemotaxis requires a continuous supply of methionine. (d) Methylation is abnormal in various mutants having defective or missing flagella.
Chemotactic responses are mediated by modulation of the frequency of tumbling. Studies with methionine auxotrophs of wild-type Eseherichis cofi and four mutants which tumble continuously show that methionine or one of its metabolites is involved in the tumbling process. Following removal of methionine, the wild type and two mutants, after various periods of time, became unable to tumble. (4), and stimulated by addition of repellent (4) or dilution of attractant (2).Since modulation of the tumbling frequency is the process through which chemotactic responses are mediated, it is necessary to understand how tumbles are generated and regulated and further how this regulation is influenced by changes in the concentrations of stimulatory compounds. Adler and Dahl (5) have observed that a methionine auxotroph of Escherichia coil K12 requires L-methionine for both chemotaxis and a normal spontaneous tumbling frequency. Recently Aswad and Koshland (6), in extending these results to Salmonella typhimurium, reported that a methionine auxotroph of a strain normal for chemotaxis was unable to tumble when starved for methionine. They also found that a similarly treated tumbling mutant (a strain which tumbles incessantly with little or no smooth swimming) continued to tumble. However, the period of smooth swimming which occurs in this mutant upon addition of the attractant aspartate was considerably lengthened as compared to that observed in the presence of methionine. Aswad and Koshland interpret these results to mean "that methionine metabolism is not tightly coupled to the generation of tumbles but . . . is necessary for rapid return to an environment that allows tumbling from an environment that causes smooth swimming" (6).Using methionine auxotrophs of E. coli K12, both chemotactic wild type and four tumbling mutants, we have investigated further the role of methionine in tumbling and the regulation of tumbling by chemotactic compounds. When starved of methionine, the wild type and two of the mutants, after different periods of time, become unable to tumble. If the starvation is performed in the presence of a constant level of attractant, the time required for the loss of tumbling is considerably decreased and in addition a third strain becomes unable to tumble. We conclude from these results that methionine or one of its metabolites is (1) required for tumbling to occur and (2) involved in converting chemical stimuli into bacterial responses. METHODSBacteria. Tumbling mutants AW618, AW620, AW627, and AW628, henceforth called mutants III, II, I, and IV, were independently isolated from E. coil AW574 (7) followed mutagenesis with ethyl methanesulfonate by R. W. Reader and W.-W. Tso. All strains were made MeF (methionine-requiring) by cotransduction with rif of the metF marker in strain 2-46 (8). The lesions in mutants I, II, and IV were found to be in cheB by complementation. The defect in mutant III has not been located.Growth and Manipulation of Bacteria. Cells were grown aerobically with rotary shaking at 350 o...
Normal Escherichia coli bacteria are repelled by acetate, benzoate, and indole and attracted by alpha-aminoisobutyrate. We have isolated mutants that are attracted to acetate, benzoate, and indole and may be repelled by alpha-aminoisobutyrate. These reversed-taxis mutants are defective in a central processing component: a set of methylated proteins known as MCP 1. The mechanism of reversal of taxis is discussed.
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