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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).
Sulfide Oxidation. Under aerobic conditions, sulfide is oxidized to sulfur and then sulfate by sulfur oxidizing bacteria, such as Thiobacillus, Beggiatoa and many others. Under anaerobic conditions, sulfide can be oxidized to sulfur and then sulfate by Purple and Green sulfur bacteria. H 2 S → S 0 → SO 2− 4. Sulfur Oxidation
These bacteria thrive when there is a gradient between oxygenated and anoxic zones, that can occur around hydrothermal vents. This is where Thiotrichales usually form microbial mats and biofilms is sulfur is abundant. This species of microbe can also be present in cold seep ecosystems where methane and sulfide seep through the seafloor.
The bacterial oxidation process comprises contacting refractory sulfide ROM ore or concentrate with a strain of the bacterial culture for a suitable treatment period under an optimum operating environment. The bacteria oxidise the sulfide minerals, thus liberating the occluded gold for subsequent recovery via cyanidation.
Some bacteria use light energy to couple sulfur oxidation to carbon dioxide (CO 2) fixation for growth. These fall into two general groups: green sulfur bacteria (GSB) and purple sulfur bacteria (PSB). [6] However, some Cyanobacteria are also able to use hydrogen sulfide as an electron donor during anoxygenic photosynthesis. [7]
In autotrophic Beggiatoa, sulfide is a source of energy and electrons for carbon fixation and growth. The oxidation of sulfide can be aerobic or anaerobic, in fact it can be coupled with the reduction of oxygen or with the reduction of nitrate.
Anaerobic sulfide oxidation is performed by both phototrophs and chemotrophs. Green sulfur bacteria (GSB) and purple sulfur bacteria (PSB) perform anoxygenic photosynthesis fueled by sulfide oxidation. Some PSB can also perform aerobic sulfide oxidation in the presence of oxygen and can even grow chemoautotrophically under low light conditions ...
Sulfide oxidation produces sulfuric acid, which dissolves the limestone walls of the cave. [6] Microcrystalline gypsum precipitates as a corrosion residue that eventually limits pH buffering by the underlying limestone and enables the development of extremely acidic wall surfaces. [6] A. thiooxidans is known to inhabit these biofilms.