Component of the Rhodospirillum centenum photosensory apparatus with structural and functional similarity to methyl-accepting chemotaxis protein chemoreceptors

Photosynthetic bacteria respond to alterations in light conditions by migra ting to locations that allows optimal use of light as an energy source. Stu dies have indicated that photosynthesis-driven electron transport functions as an attractant signal for motility among purple photosynthetic bacteria, However, it is unclear just how the motility-based signal transduction sys tem monitors electron how through photosynthesis-driven electron transport. Recently, we have demonstrated that the purple photosynthetic bacterium Rh odospirillum centenum is capable of rapidly moving swarm cell colonies towa rd infrared light as well as away from visible light. Light-driven colony m otility of R. centenum has allowed us to perform genetic dissection of the signaling pathway that affects photosynthesis-driven motility, In this stud y, we have undertaken sequence and mutational analyses of one of the compon ents of a signal transduction pathway, Ptr, which appears responsible for t ransmitting a signal from the photosynthesis-driven electron transport chai n to the chemotaxis signal transduction cascade. Mutational analysis demons trates that cells disrupted for ptr are defective in altering motility in r esponse to light, as well as defective in light-dependent release of methan ol. We present a model which proposes that Ptr senses the redox state of a component in the photosynthetic cyclic electron transport chain and that Pt r is responsible for transmitting a signal to the chemotaxis machinery to i nduce a photosynthesis-dependent motility response.