Phototaxis in Archaea and Bacteria
Jon Riggs, Wouter D.Hoff
Oklahoma State University, Stillwater, OK, United States.
Light-triggered changes in the motility of archaea and bacteria during phototaxis involves multiple photoreceptors, signaling pathways, and motility systems, as demonstrated by studies on four model systems. In Halobacterium salinarum two sensory rhodopsins relay light signals to methyl accepting chemotaxis proteins leading to the archaellum via homologs of CheA and CheY and trigger negative and positive phototaxis responses depending on the color of the excitation. In Rhodobacter sphaeroides excitation of the photosynthetic machinery results in changes of redox potential that trigger changes in rotation direction of the flagellar motor. Halorhodospira halophila contains a similar system for positive phototaxis, but also contains photoactive yellow protein, a dedicated photoreceptor for negative phototaxis in this organism. Synechocystis moves by gliding motility based on type IV pili and contains a complex array of photosensory systems, with a major role for bilin-containing members of the phytochrome superfamily. This organism exhibits social phototaxis of entire colonies, while single Synechocystis cells are capable of true phototaxis. The mechanism that allows this directional detection involves microlensing by the spherical cells. While rich information is available for the molecular mechanism of photoreceptor activation and changes in cellular mobility, more research is needed on the signal transduction pathways that convert photoreceptor activation to changes in the cellular motility machinery.
Keywords: BLUF domain, Cellular microlensing, Cyanobacteria, Cyanobacteriochrome, Flagellum, Halobacterium, Halorhodospira, Photoactive yellow protein, Photomovement, Photoreceptors, Photosynthesis, Phototaxis, Rhodobacter, Sensory rhodopsin, Signal transduction.