Photoresponses of Halobacterium salinarum to Repetitive Pulse Stimuli

Abstract

Halobacterium salinarum cells from 3-day-old cultures have been stimulated with different patterns of repetitive pulse stimuli. A short train of 0.6-s orange light pulses with a 4-s period resulted in reversal peaks of increasing intensity. The reverse occurred when blue light pulses were delivered as a finite train: with a 3-s period, the response declined in sequence from the first to the last pulse. To evaluate the response of the system under steady-state conditions of stimulation, continuous trains of pulses were also applied; whereas blue light always produced a sharply peaked response immediately after each pulse, orange pulses resulted in a declining peak of reversals that lasted until the subsequent pulse. An attempt to account for these results in terms of current excitation/adaptation models shows that additional mechanisms appear to be at work in this transduction chain.

Effect of loss of CheC and other adaptational proteins on chemotactic behaviour in Bacillus subtilis

“…Many archaea and some bacteria have CheC or the closely related CheX (Kirby et al, 2001). Some of these have polar flagella and, on negative stimuli, undergo repeated reversals of motion, such as the spirochaete Spirochaeta aurantia (Cercignani et al, 1998;Fosnaugh & Greenberg, 1988) and the archaeon Halobacterium salinarum (Spudich et al, 1989). It is clear that the main output of the receptor/CheA complex is to regulate CheY-P levels in these as in all chemotactic bacteria/ archaea but how CheY-P levels can regulate switching frequency (it primarily affects bias) has never been understood.…”

Competition-Integration of Blue and Orange Stimuli in Halobacterium salinarum Cannot Occur Solely in SRI Photoreceptor

“…The existence of two cytoplasmic signals could also account for the color specificity of reported delayed effects of stimuli, occurring after the delivery of a stimulus on a time scale much longer than that of the photocycle (Mac-Cain et al, 1987;Lucia et al, 1996Lucia et al, , 1997Cercignani et al, 1998).…”

Color-specific Conditioning Effects Due to Both Orange and Blue Stimuli Are Observed in a Halobacterium salinarum Strain Devoid of Putative Methylatable Sites on HtrI¶

“…When the conditioning stimulus is a blue pulse, the poststimulus effect results in a general inhibition; either an orange step down or a blue pulse induce a much weaker reversal peak when delivered a few seconds after an intense blue pulse. This has been indirectly shown using several stimuli in sequence (2,3) or using repetitive stimulation (4), which is a suitable method to enhance the “memory” arising from the prolonged effects of light stimuli.…”