Details for Chromatiales

The purple phototrophic bacteria carry out anoxygenic photosynthesis; unlike the cyanobacteria no O₂ is evolved. Purple bacteria contain chlorophyll pigments called bacteriochlorophylls and additionally contain any of a variety of carotenoid pigments. Together, these pigments give purple bacteria their spectacular colors, usually purple, red, or brown. The purple bacteria are a morphologically diverse group, and the taxonomy of these organisms has been established along phylogenetic, morphological, and physiological lines.

Purple bacteria synthesize intracytoplasmic photosynthetic membrane systems into which their pigments are inserted. These membranes can be of various morphologies but in all cases originate from invaginations of the cytoplasmic membrane. These internal membranes allow purple bacteria to increase their specific pigment content and to thus better utilize the available light; when cells are grown at high light intensities, internal membranes are few and pigment contents low, while at low light intensities, the cells are packed with membranes and photopigments.