Novel sensory adaptation mechanism in bacterial chemotaxis to oxygen and phosphotransferase substrates

The involvement of methylation in the chemosensory response of bacteria to many attractants has been clearly established by studies in several laboratories. It has been assumed that adaptation of Salmonella typhimurium and Escherichia coli to all attractants involves methylation of a transmembrane methyl-accepting chemotaxis protein. The methyl donor in this reaction is S-adenosyl-L-methionine, and the protein methyltransferase is the product of the cheR gene. In contrast, adaptation to oxygen and phosphotransferase substrates were found to be independent of this methylation system. In E. coli AW660 (tsr tar trg), which lacks the known methyl-accepting chemotaxis proteins, chemotaxis was normal to oxygen and to substrates of the phosphotransferase system such as D-mannose, D-glucose, and N-acetyl-D-glucosamine. When S-adenosyl-L-methionine was depleted by methionine starvation or by addition of 1-aminocyclopentane-1-carboxylic acid, methylation-dependent adaptation to serine, aspartate, and ribose was defective in wild-type E. coli and S. typhimurium. However, adaptation to oxygen and phosphotransferase substrates was independent of S-adenosyl-L-methionine and the cheR product. These results suggest that there are methylation-independent and methylation-dependent mechanisms for sensory adaptation in bacteria.