The role of methylation in the taxis of Halobacterium halobium to light and chemo‐effectors

In Halobacterium halobium tactic responses towards light and chemoeffectors are accompanied by changes in the methylation level of methyl‐accepting chemotaxis proteins (MCP). Taxis towards green light absorbed by the bacteriorhodopsin proton pump appears to be governed by Δ H+ ‐sensing. The addition of CCCP, an uncoupler, prevented the increase of MCP methylation in response to green light illumination, but had no effect on CH 3 ‐incorporation followed by the addition of the attractants glucose, leucine and histidine. Similarly, CCCP did not change MCP demethylation in response to blue light illumination, a repelling stimuli. The sensitivity to an uncoupler of methylation linked to Δ H +‐mediated green light taxis is to be expected, while the independence of demethylation caused by the blue light of CCCP is an indication that in the latter case a specific photoreceptor governs phototaxis. Informed processing from the blue light receptor to MCP does not involve a change in the membrane potential.