Addition of chemotactic attractant to B. subtilis brought about a transient increase of absorption at 557 nm, compared with absorption at either 543 or 575.5 nm. The increase was tentatively attributed to reduction of cytochrome b. This reduction was linked to the ability of attractants (and certain other reagents) to make all bacteria in a population swim smoothly, rather than sometimes swimming and sometimes tumbling as they normally do. It is thought to signify a higher energy requirement for swimming since, in tumbling, flagella may tangle and jam, resulting in periods of no energy loss. Cations were required for motility; the function of the cations was probably not to energize motility, since protons alone could do that, but rather to reduce the surface potential of cells and, thus, avoid excess local acidity.
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