Microorganisms uptake zero-valent sulfur via membrane lipid dissolution of octasulfur and intracellular...

Zero-valent sulfur, commonly utilized as a fertilizer or fungicide, is prevalent in various environmental contexts. Its most stable and predominant form, octasulfur (S₈), plays a crucial role in microbial sulfur metabolism, either through oxidation or reduction. However, the mechanism underlying its cellular uptake remains elusive. We presented evidence that zero-valent sulfur was adsorbed to the cell surface and then dissolved into the membrane lipid layer as lipid-soluble S₈ molecules, which reacted with cellular low-molecular thiols to form persulfide, e.g., glutathione persulfide (GSSH), in the cytoplasm. The process brought extracellular zero-valent sulfur into the cells. When persulfide dioxygenase is present in the cells, GSSH will be oxidized. Otherwise, GSSH will react with another glutathione (GSH) to produce glutathione disulfide (GSSG) and hydrogen sulfide (H₂S). The mechanism is different from simple diffusion, as insoluble S₈ becomes soluble GSSH after crossing the cytoplasmic membrane. The uptake process is limited by physical contact of insoluble zero-valent sulfur with microbial cells and the regeneration of cellular thiols. Our findings elucidate the cellular uptake mechanism of zero-valent sulfur, which provides critical information for its application in agricultural practices and the bioremediation of sulfur contaminants and heavy metals.