Bacterial chemotaxis, the movement of motile bacteria toward or away from chemicals, was discovered nearly a century ago by Engelmann (43) and Pfeffer (70, 71) The subject was actively studied for about fifty years, but then there were very few reports until quite recently For reviews of the literature up to about 1960, see Berg (23) , Weibull (90) and Ziegler (92) The present review will restrict itself to the recent work on chemotaxis in Escherichia coli and Salmonella typhimurium, some of which is also covered in Berg’s review (23)

Chemotaxis in bacteria.

Bacteria must constantly adapt their growth to changes in nutrient availability; yet despite large-scale changes in protein expression associated with sensing, adaptation, and processing different environmental nutrients, simple growth laws connect the ribosome abundance and the growth rate. Here, we investigate the origin of these growth laws by analyzing the features of ribosomal regulation that coordinate proteome-wide expression changes with cell growth in a variety of nutrient conditions in the model organism Escherichia coli. We identify supply-driven feedforward activation of ribosomal protein synthesis as the key regulatory motif maximizing amino acid flux, and autonomously guiding a cell to achieve optimal growth in different environments. The growth laws emerge naturally from the robust regulatory strategy underlying growth rate control, irrespective of the details of the molecular implementation. The study highlights the interplay between phenomenological modeling and molecular mechanisms in uncovering fundamental operating constraints, with implications for endogenous and synthetic design of microorganisms.

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Emergence of robust growth laws from optimal regulation of ribosome synthesis

Methylation of membrane-bound proteins with apparent molecular weights around 65,000 does not occur in mutants of the generally nonchemotactic cheR class of Salmonella typhimurium. This was shown to be due to the lack of a protein methyltransferase in these mutants by means of an in vitro assay using soluble proteins, membranes, and S-adenosylmethionine as the methyl donor. The methylase from the wild type was purified, characterized, and shown to be of molecular weight 38,000. It is specific for proteins in S. typhimurium and Escherichia coli membranes. The methylase is not required for tumbling but appears to be essential for maintaining the appropriate rate constants and levels of the regulator of the chemotactic response.

https://www.pnas.org/content/pnas/74/2/533.full.pdf

Identification of a protein methyltransferase as the cheR gene product in the bacterial sensing system

The source of energy for bacterial motility is the intermediate in oxidative phosphorylation, not ATP directly. For chemotaxis, however, there is an additional requirement, presumably ATP. These conclusions are based on the following findings. (i) Unlike their parents, mutants of Escherichia coli and Salmonella typhimurium that are blocked in the conversion of ATP to the intermediate of oxidative phosphorylation failed to swim anaerobically, even when they produced ATP. When respiration was restored to the mutants, motility was simultaneously restored. (ii) Carbonylcyanide m-chlorophenylhydrazone, which uncouples oxidative phosphorylation, completely inhibited motility even though ATP remained present. (iii) Arsenate did not inhibit motility in the presence of an oxidizable substrate, though it did reduce ATP levels to less than 0.3% (iv) Arsenate completely inhibited chemotaxis under conditions where motility was normal.

Chemomechanical coupling without ATP: the source of energy for motility and chemotaxis in bacteria.

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.

https://www.pnas.org/content/pnas/72/10/3939.full.pdf

Methylation of a membrane protein involved in bacterial chemotaxis

A spontaneous ethionine-resistant mutant of Escherichia coli was found to be nonchemotactic. The mutant had low S-adenosylmethionine (SAM) synthetase activity and a greatly reduced SAM pool. Transd...

An S-adenosylmethionine requirement for chemotaxis in Escherichia coli.

Auxotrophic strains of Escherichia coli generally are motile and chemotactic in the absence of those amino acids needed for growth. Methionine auxotrophs, however, require low levels of methionine ...

Chemotaxis and methionine metabolism in Escherichia coli.

Six methionine auxotrophs were isolated from an E. coli K-12 strain which required up to 100 times as much methionine for growth as a conventional auxotroph. In these mutants, the methionyl-tRNA synthetase had an increased Km for methionine. The Km value for the mutants ranged from 0.48 to 1.63 mM, compared to 0.078 mM for the wild type. The Km (methionine) for S-adenosyl methionine synthetase was not altered.

John B. Armstrong

Papers

An S-adenosylmethionine requirement for chemotaxis in Escherichia coli.

Chemotaxis and methionine metabolism in Escherichia coli.

A new method for the isolation of methionyl transfer RNA synthetase mutants from Escherichia coli.