Coloured scanning electron micrograph (SEM) of Chromatium sp., photoautotrophic, anaerobic, rod-shaped, Gram-negative bacterium. Chromatium species are photoautotrophic bacteria called purple sulphur bacteria. They exhibit bacterial photosynthesis whereby ATP is produced by cyclic photophosphorylation in the presence of light and bacteriochlorophyll A. Sulphide (such as hydrogen sulphide) is oxidized to produce sulphur granules in the cell cytoplasm. The sulphide is also converted in to sulphate which may serve as a cellular reserve. They are found in both freshwater and saltwater, especially in stagnant water. Magnification: x4,400 when shortest axis printed at 25 millimetres.
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