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A sulfur globule is an intracellular, and sometimes extracellular, aggregate used by various sulfur oxidizing bacteria as storage for elemental sulfur.Sulfur globules were first explained in 1887 by Sergei Winogradsky, [1] and their complete structure and chemical composition has been a debate since then. [1]
Iron-oxidizing bacteria are chemotrophic bacteria that derive energy by oxidizing dissolved ferrous iron. They are known to grow and proliferate in waters containing iron concentrations as low as 0.1 mg/L. However, at least 0.3 ppm of dissolved oxygen is needed to carry out the oxidation. [10]
Aerobic sulfide-oxidizing bacteria usually oxidize sulfide to sulfate and are obligate or facultative chemolithoautotrophs. The latter can grow as heterotrophs , obtaining carbon from organic sources, or as autotrophs, using sulfide as the electron donor (energy source) for CO 2 fixation. [ 4 ]
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
Beggiatoa group is mainly composed by chemolithotrophic, sulfide-oxidizing bacteria. However, the range of possible metabolic pathways is very diversified, varying from the heterotrophy to the chemolithoautotrophy. Because of this huge variability the diverse bacteria of this genus can differ greatly from each other. [15]
Most species oxidize sulfur compounds for energy metabolism. They often use nitrate as an electron acceptor, which contributes to the detoxification of sulfide-rich environments. These bacteria thrive when there is a gradient between oxygenated and anoxic zones, that can occur around hydrothermal vents.
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]