The Family Chromatiaceae

The Chromatiaceae is a family of the Chromatiales within the Gammaproteobacteria and closely related to the Ectothiorhodospiraceae. Representatives of both families are referred to as phototrophic purple sulfur bacteria and typically grow under anoxic conditions in the light using sulfide as photosynthetic electron donor, which is oxidized to sulfate via intermediate accumulation of globules of elemental sulfur. In Chromatiaceae species, the sulfur globules appear inside the cells; in Ectothiorhodospiraceae, they are formed outside the cells and appear in the medium. Characteristic properties of these bacteria are the synthesis of photosynthetic pigments, bacteriochlorophyll a or b, and various types of carotenoids and the formation of a photosynthetic apparatus with reaction center and antenna complexes localized within internal membrane systems. Phototrophic growth, photosynthetic pigment synthesis, and formation of the photosynthetic apparatus and internal membranes are strictly regulated by oxygen and light and become derepressed at low oxygen tensions. Typically, Chromatiaceae are enabled to the photolithoautotrophic mode of growth. A number of species also can grow photoheterotrophically using a limited number of simple organic molecules. Some species also can grow under chemotrophic conditions in the dark, either autotrophically or heterotrophically using oxygen as terminal electron acceptor in respiratory processe