Chemotactic methylesterase promotes adaptation to high concentrations of attractant in Bacillus subtilis

The Bacillus subtilis gene encoding CheB (cheB(B)), the chemotactic methylesterase, has been sequenced. The 39-kDa protein which resulted from the expression of cheB(B), using a T7 expression system was consistent with the predicted open reading frame. CheB(B) shares 39.5% identity with Escherichia coli CheB(E) and can complement a cheB(E) null mutant. CheB(B) is required for removal of methyl groups from the receptors upon attractant stimulus and appears to play an important role in adaptation to the addition of attractants, whereas CheB(E) plays an important role in adaptation to the addition of repellents. Unlike the cheB(E) and cheR(E) mutants of E. coli, which show extreme flagellar rotational biases, the unstimulated cheB(B) mutant showed a normal (wild type) bias. Upon addition of attractant, the cheB(B) null mutant showed a counter-clockwise bias that was higher than for wild type and demonstrated only partial adaptation. In the capillary assay for the attractant azetidine-2-carboxylic acid, the mutant gave a wild type response at low concentrations but a very reduced response at high concentrations. We conclude that B. subtilis has an effective methylation- independent adaptation system but must utilize the methylation system for adaptation to high concentrations of attractant.