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Rhodospirillaceae (purple non-sulphur bacteria; order Rhodospirillales) A family of anaerobic, anoxygenic, photosynthetic bacteria which mostly use organic compounds as sources of reduction for photosynthesis. Most species are motile, having flagella. The cells are spherical, spiral, ovoid, or rod-shaped, and range in colour from brownish or greenish to purple. Photosynthetic pigments are attached to membranes which are continuous with the cytoplasmic membrane. There are several genera. The organisms are found in mud in eutrophic ponds, ditches, sewage lagoons, etc.