Thermal Organism: Chromatium sp. NZ

Purple bacteria that utilize hydrogen sulfide (H₂S) as an electron donor for CO₂ reduction to photosynthesis are known as puple sulfur bacteria. The sulfide is oxidized to elemental sulfur (S⁰) that is stored in globules inside the cells; the sulfur later disappears as it is oxidized to sulfate. Many purple sulfur bacteria can also use other reduced sulfur compounds as photosynthetic electron donors, thiosulfate (S₂O₃^2-) being a key one commonly used to grow laboratory cultures of these organisms.

Purple sulfur bacteria are generally found in illuminated anoxic zones of lakes and other aquatic habitats where H₂S accumulates, and also in "sulfur springs," where geochemically or biologically produced H₂S can trigger the formations of blooms of purple sulfur bacteria. The most favorable lakes for development of puple sulfur bacteria are meromictic (permanently stratified) lakes. Meromictic lakes stratify because they have denser (usually saline) water in the bottom and less dense (usually freshwater) nearer the surface. If sufficient sulfate is present to support sulfate reduction, the sulfide, produced in the sediments, diffuses upward into the anoxic bottom waters, and here purple sulfur bacteria can form massive blooms, usually in association with green sulfur phototrophic bacteria.

For more information on Purple Phototrphic Bacteria click here.

Taken from the text Brock Biology of Microorganisms (10th ed.). Madigan, M.T., Martinko, J.M., and Parker, J. 2003. Prentice Hall. 355p.