Sulfur lithotrophs are a group of bacteria that use inorganic sulfur compounds, such as elemental sulfur or hydrogen sulfide, as an energy source for metabolism. Elemental sulfur (S0) can be a particularly challenging substrate for these organisms to use, as it is insoluble and can be toxic at high concentrations.
However, certain sulfur lithotrophs have evolved mechanisms to overcome the toxic effects of elemental sulfur. One strategy used by these organisms is to oxidize the elemental sulfur to sulfate (SO4^2-), which is less toxic to the cell. This process involves the action of sulfur oxidizing enzymes, such as sulfur oxygenase/reductase or thiosulfate oxidase, which convert elemental sulfur to sulfite (SO3^2-) or thiosulfate (S2O3^2-), respectively. These intermediates can then be further oxidized to sulfate by other enzymes, such as sulfite oxidase or thiosulfate dehydrogenase.
Another strategy used by some sulfur lithotrophs is to store elemental sulfur intracellularly in specialized compartments called sulfur globules. These globules are thought to help sequester the sulfur and prevent it from interacting with cellular components that could be damaged by its toxic effects.
Finally, some sulfur lithotrophs have evolved mechanisms to detoxify elemental sulfur by reducing it to hydrogen sulfide (H2S), which is less toxic than S0. This process is mediated by the action of sulfur-reducing enzymes, such as sulfur reductase or thiosulfate reductase.
Overall, these mechanisms allow certain sulfur lithotrophs to effectively use elemental sulfur as an energy source, while minimizing its toxic effects on the cell.