The proton pump bacteriorhodopsin is a photoreceptor transdwtion in Halobacterium halobium December I 99 1 for signal

Ffulohucreriuttt hulohiuttt swims by rotating its pohtrly inserted fiagcllar bundle. The cells arc attracted by green-to-orange light which they can use for photophosphorylation but Ret damaging blue or ultraviolet light. It is petterally believed that this kind of ‘colour vision’ is achieved by the combined action of two photoreceptor proteins. sensory rhodopsins-I and -II, that switch in the light the rotational sense of the bundle and in c”,.~c~ur..cr. ------‘*-_-_ “1. =~mmtnn ~tr~~rinn of a cell. Bv cxoressine the bacteriorhodopsin gene in a photoreceptor-negative background we have now ..I_ “. . . . . . . . . . . .~ _..__..___ demonstrated the existence of a proton-motive f&ce’sensor-(protomctcr) and the function of bacteriorhodopsin as an additionai photoreceptor covering the high intensity range. When the bactcriorhodopsin-gcncrated proton-motive force drops caused by a sudden decrease in light intensity, the cells respond by reversing their swimming direction. This response dots not occur when the proton-motive force is saturated by respiration or t%rmentation.