Sulfur oxidizing bacteria
Sulfur-reducing bacteria or Sulfurikanten are autotrophic bacteria , the hydrogen sulfide (H 2 S) and other reduced sulfur compounds, such as (S, for example, thiosulfate 2 O 3 2- ), to elemental sulfur (S) or sulfate oxidize . Most can also oxidize elemental sulfur to sulfate. The non-phototrophic (“colorless”) sulfur-oxidizing bacteria form a metabolic type, not a phylogenetic unit. Many groups are therefore not related and can be found in very different taxa .
Sulfur oxidizing bacteria are sometimes also called sulfur bacteria , but this term is ambiguous, it is applied to different metabolic types of bacteria.
Two physiological groups of sulfur-oxidizing bacteria are distinguished:
Non-phototrophic sulfur oxidizing bacteria . These bacteria cover their energy needs through exergonic sulfur oxidation. This group includes, for example, Acidithiobacillus thiooxidans (unicellular, aerobic, acidophilic), Beggiatoa (multicellular, filamentous, aerobic, non-acidophilic), many endolithic bacteria and also the Thiomargarita namibiensis , discovered in 1999 , the "sulfur pearl of Namibia", which has a Diameter of up to three quarters of a millimeter the largest bacteria that is visible to the naked eye.
Photoautotrophic sulfur oxidizing bacteria . These bacteria have bacteriochlorophyll and use hydrogen sulfide (H 2 S) or other reduced sulfur compounds as an electron source ( reductant ) for anoxygenic photosynthesis . This group includes the obligatory anaerobic “ green sulfur bacteria ” (for example the genus Chlorobium ) and the likewise obligatory anaerobic “ sulfur purple bacteria ” (for example the genus Chromatium ).
Cyanobacteria carry out an oxygenic photosynthesis. They therefore have two photosystems and can use water as an electron source for the reduction of carbon dioxide (with the formation of elemental oxygen). However, some cyanobacteria can also use hydrogen sulfide as an electron source when hydrogen sulfide is present (with the formation of elemental sulfur) and in this case only use photosystem I, they then carry out anoxygenic photosynthesis. They can therefore be assigned to the second group, the photoautotrophic sulfur bacteria. The ability to use hydrogen sulfide as a reductant is interpreted as a relic of the evolution of oxygenic photosynthesis from anoxygenic.
See also
literature
- Joseph W. Lengeler, G. Drews, Hans Günter Schlegel: Biology of the prokaryotes . Thieme, Stuttgart 1999, ISBN 3-13-108411-1 , p. 245-251 .