Genetics and Photophysiology of Novel Anoxyphototrophs

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9303836 Bauer The recently described nonsulfur purple photosynthetic bacterium Rhodospirillum centenum exhibits several physiological traits previously unknown among photosynthetic eubacteria. One feature is the existence of a life cycle involving the formation of heat and desiccation resistant cysts. Germination of Rsp. centenum cysts leads to cell differentiation characterized by swarm cell behavior on solid media. Swarm cells grown on solid agar medium have numerous lateral flagella and are distinct from non-swarm cells which bear a single polar flagellum. Swarm cell differentiation appears to be a stage of a life cycle and to be a specific response to an increase in medium viscosity. A second unusual feature of Rsp. centenum is that swarm cell colonies have the capacity to migrate rapidly either towards or away from light; rates as high as 45 mm/hour have been observed. An action spectrum has demonstrated that 585 nm light repels whereas light over the region 800-880 nm attracts. Major goals of this proposal include the physiological characterization of swarm cells as well as an analysis of phototactic behavior of Rsp. centenum. In addition, genetic analyses of swarm cell formation as well as phototaxis will be undertaken to determine the number and nature of the genetic loci involved in these processes. These studies will also be augmented by biochemical and molecular genetic characterization of the photoreceptor(s) involved. It is anticipated that the proposed research will provide significant information on prokaryotic cell differentiation and in addition, should provide the first molecular analysis of the mechanism of phototaxis in eubacteria. We also propose to extend genetic analysis of bacterial photosynthesis to evolutionarily divers species of eubacterial phototrophs. The aim of this area of research is to obtain clones of bacteriochlorophyll biosynthesis genes from Chlorobium tepidum, Heliobacterium gestii, Rhodopseudomonas viridis and cyanobacteria for the purpose of determining the extent to which a Photosynthesis Gene Cluster is conserved among various genera and species of phototrophic prokaryotes. The clones obtained will also be used to generate sequence analyses of genetic loci common to bacterial and plant chlorophyll biosynthetic pathways for use in subsequent studies of chlorophyll biosynthesis in plant systems. ***