Light-induced behavioral responses ('phototaxis') in prokaryotes

Light-induced sensory responses are among the oldest scientific observations on bacterial behavior. Various types of response have been characterized physiologically in detail. However, the molecular basis of this type of response is only slowly emerging. In many of these systems photosynthetic pigments absorb the light. This then generates a signal via electron transport, feeding into a canonical chemotaxis signal transduction pathway. Nevertheless, several examples have been identified in which dedicated photoreceptor proteins do play a role. The intrinsic complexity of some of these signal transduction systems is overwhelming, in part because of the significant apparent redundancy. The genomics information that is now available for several model organisms ( in particular Rhodobacter sphaeroides and Synechocystis sp. PCC6803) facilitates obtaining an increasingly detailed view of the molecular basis of the partial reactions that jointly form the basis of this type of elementary behavioral response.