Nutrient-stimulated methylation of a membrane protein in Bacillus licheniformis

When nitrogen-starved vegetative cells of Bacillus licheniformis A5 were presented with a good nitrogen source in the presence of chloramphenicol and methyl-labeled methionine, a 40-kilodalton (kDa) protein was found to be reversibly methylated, with a half-life of approximately 10 to 15 min. The 40-kDa protein was strongly methylated in response to the addition of ammonia, glutamine, or sodium glutamate nitrogen sources that produce generation times of less than or equal to 90 min) but was very poorly methylated in the absence of a nitrogen source or in the presence of potassium glutamate or histidine (generation times of greater than 150 min). The methylated protein was found to be membrane associated, but the methylation reaction did not appear to be related to chemotaxis, because the spectrum of nutrients that promoted methylation was different from that which prompted a chemotactic response. In addition, the methyl residue on the 40-kDa protein was found to be alkali stable. Approximately 180 to 640 molecules of the methylated protein were found per cell. The characteristics of this methylated protein were consistent with the hypothesis that the reversible methylation of the protein functions in nutrient sensing to regulate growth, cell division, and the initiation of sporulation.