sulfur bacteria

The rather confusing term 'sulfur bacteria' encompasses green sulfur bacteria plus purple sulfur bacteria (distinguised from green nonsulfur and purple nonsulfur bacteria) .

The green sulfur bacteria (Chlorobiaceae) are photosynthetic bacteria that form a coherent group phylogenetically isolated from all other microbes, such that they are the sole occupants of their phylum (Phylum Chlorobi).

The purple sulfur bacteria are photosynthetic anaerobic or microaerophilic Proteobacteria found in meromictic lakes and sulfur (hot) springs.

Chlorobiaceae (green sulfur) are anaerobic obligate photoautolithotrophs that use sulfide, elemental sulfur or hydrogen as their source of electrons, employing bacteriochlorophylls c, d, and e in vesicles called chlorosomes that are attached to the membrane. As anaerobes, their environment must be oxygen-free, and, as phototrophs, they require light as an energy source.

In conducting nonoxygenic photosynthesis, green and purple sulfur bacteria employ sulfide ions (H2S) as an electron donor:

CO2 + 2H2S → CH2O + H2O + 2S

Members of the purple Chromatiaceae family produce internal sulfur granules, while members of the Ectothiorhodospiraceae family produce external sulfur granules on oxidation of H2S.

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