FIG. 3.

The cheBR mutant is impaired in, but not null for, aerotaxis in a spatial gradient assay. The abilities of the A. brasilense wild-type strain (Sp7) and the cheBR mutant to form a sharp aerotaxis band in a gradient of oxygen in a capillary tube were compared. The wild-type strain (Sp7) forms a sharp aerotaxis band, while the cheBR mutant forms a diffuse band at a different position in the gradient. Malate (10 mM) was added as the sole carbon and energy source to the suspension of motile cells. The cheB and cheR mutants did not form any aerotaxis bands under similar conditions (not shown). Arrows point to the center of the aerotaxis bands.