The Phototrophic Beta-Proteobacteria

Abstract

he phototrophic purple β-Proteobacteria are purple nonsulfur bacteria able to perform anoxygenic photosynthesis with bacteriochlorophylls and carotenoids as photosynthetic pigments. Though genetic relationships and chemotaxonomic properties clearly distinguish these bacteria from the phototrophic α-Proteobacteria, both groups share a number of common physiological properties. Owing to their photosynthetic pigments, cell suspensions appear in various colors and have characteristic absorption spectra. Photosynthetic pigments are located in the cytoplasmic membrane and in internal membrane systems (small tubular invaginations of the cytoplasmic membrane) and are bacteriochlorophyll a and various types of carotenoids. In most species, the formation of pigments and of the internal membrane systems is repressed under oxic conditions but becomes derepressed at low oxygen tensions.