No abstract

The attractant effect of green light and the repellent effect of blue light on Halobacterium halobium were studied. It was found that addition of CNand dicyclohexylcarbodiimide, which block the redox chain and H+-ATPase, respectively, increased both the amplitude of lightdependent changes of membrane potential (A$), monitored by the distribution of tetraphenylphosphonium, and the sensitivity of the green-light taxis. A direct proportionality between A$ and the green-light sensitivity was revealed. The sensitivity of the green-light taxis was decreased by glucose, histidine and Na+/K+ gradient, i.e. factors reducing the light-dependent changes of protonic potential. These factors did not affect the blue-light taxis. The uncoupler carbonyl cyanide m-chlorophenylhydrazone appears to repel H. halobium cells. These data are in agreement with the assumption that the green-light taxis is governed by a sensing of protonic potential, whereas the blue-light taxis is mediated by a specific photoreceptor.

No abstract

In Halobaeterium 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 A/t 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 CH3-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 AFt 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. Halobacterium halobium photobehavior a~H+-sensing Protein methylation Blue-light taxis