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.