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The oxidation of reduced sulfur compounds is performed exclusively by Bacteria and Archaea.All the Archaea involved in this process are aerobic and belong to the Order Sulfolobales, [19] [20] characterized by acidophiles (extremophiles that require low pHs to grow) and thermophiles (extremophiles that require high temperatures to grow).
The partly oxidized sulfur compounds can be either completely oxidized to sulfate by sulfur-oxidizing bacteria, if enough oxygen is present, or reduced to sulfide by sulfidogenic bacteria. In such places oxygen limitation is frequent, as indicated by micro-profile measurements from such habitats.
Sulfur metabolism. Sulfur is metabolized by all organisms, from bacteria and archaea to plants and animals. Sulfur can have an oxidation state from -2 to +6 and is reduced or oxidized by a diverse range of organisms. [1] The element is present in proteins, sulfate esters of polysaccharides, steroids, phenols, and sulfur-containing coenzymes.
Oxygen is required in both ammonia and nitrite oxidation, meaning that both nitrosifying and nitrite-oxidizing bacteria are aerobes. As in sulfur and iron oxidation, NADH for carbon dioxide fixation using the Calvin cycle is generated by reverse electron flow, thereby placing a further metabolic burden on an already energy-poor process.
The capability to oxidize sulfide and store sulfur are the main features which define Beggiatoa and its close relative Thioploca as filamentous colorless sulfur bacteria, in contrast to other filamentous bacteria like cyanobacteria and the non-sulfur-oxidizing Cytophaga and Flexibacter. [11]
Sulfide:quinone oxidoreductase (SQR) also helps with electron transport, but, when alone, has been found to produce decreased rates of sulfide oxidation in green sulfur bacteria, suggesting that there is a different, more effective mechanism. [27] However, most green sulfur bacteria contain a homolog of the SQR gene. [29]
Acidithiobacillus are chemolithoautotrophs that can occur as acidophilic, mesophilic, or mesothermophilic. [6] Acidithiobacillus caldus can also grow mixotrophically. Currently, the genus comprises ten species which are capable of obtaining energy by oxidizing sulfur compounds, with certain species also utilizing both ferrous and ferric iron.
Thiotrichales. Thiotrichales is an order of sulfur-oxidizing bacteria within the class Gammaproteobacteria. The members of this order are known for their large size and ability to live in sulfur rich environments. Thiotrichales has an important role in the sulfur and nitrogen cycles in marine and freshwater sediments, hydrothermal vents, and ...