Phototrophic sulphur bacteria Chromatium minutissimum 1 C, Ectothiorhodospira shaposhnikovii 1, and various strains of Thiocapsa roseopersicina grow in the dark under anaerobic conditions (hydrogen or argon) on organic media in the presence of sulphide, thiosulphate or molecular sulphur. Ect. shaposhnikovii grows also in the presence of sulphite, cysteine, methionine, glutathione, and, to a less degree, sulphates. Cultures of Ect. shaposhnikovii growing in the dark under anaerobic conditions assimilate fructose and liberate pyruvate, lactate, formiate and traces of acetate into the medium. These cultures can grow in the dark under anaerobic conditions assimilating not only fructose but also various C4-dicarboxylic acids, lactate, pyruvate, butyrate, and acetate. Thiocapsa grows on media containing malate, succinate, lactate, pyruvate, and acetate. Thiocapsa reseopersicina SL assimilates in the dark under anaerobic conditions fructose, glucose, glycerol, pyruvate, lactate, and acetate.