Characterization of cyst cell formation in the purple photosynthetic bacterium Rhodospirillum centenum

Department of Biology, Indiana University, Jordan Hall, Bloomington, IN 47405, USA Correspondence Carl E. Bauer cbauer{at}bio.indiana.edu Rhodospirillum centenum is an anoxygenic photosynthetic bacterium that is capable of differentiating into several cell types. When grown phototrophically in liquid, cells exhibit a vibrioid shape and have a single polar flagellum. When grown on a solid surface, R. centenum will differentiate into rod-shaped swarm cells that display numerous lateral flagella. Upon starvation for nutrients, R. centenum also forms desiccation-resistant cysts. In this study, it was determined that R. centenum has heat- and desiccation-resistance properties similar to other cyst-forming species. In addition, microscopic analyses of the morphological changes that occur during cyst cell development were performed. It was observed that R. centenum typically forms multi-celled clusters of cysts that contain from four to more than 10 cells per cluster. It was also determined that cell density has a minor effect on the percentage of cyst cells formed, with cell densities of 10 5 –10 7 cells per 5 µl spot yielding the highest percentage of cyst cells. The striking similarities between the life cycle of R. centenum and the life cycle exhibited by Azospirillum spp. are discussed. Abbreviations: PHB, poly-hydroxybutyrate