A common mechanism for rapid transfer of zero-valent sulfur between microbial cells

Zero-valent sulfur is accumulated in the cytoplasm of certain sulfur-oxidizing or reducing microorganisms. When these microorganisms are unable to metabolize zero-valent sulfur, they produce sulfur globules that mainly consist of octasulfur (S₈), a common species of elemental sulfur. The intracellular zero-valent sulfur was easily transferred to other bacteria and the yeast Saccharomyces cerevisiae for metabolism. After eliminating all known potential mechanisms of zero-valent sulfur transfer between cells, we hypothesized and tested whether S₈ was directly transferred. S₈ was shown to be soluble and enriched in membrane lipids. The transfer of S₈ molecules occurred between live cells, inactivated cells, and liposomes via physical contact. Low-molecular thiols, such as glutathione, reacted with S₈ in the cell membranes to produce glutathione persulfide that was soluble in the cytoplasm. In the recipient cells, glutathione persulfide was either metabolized by enzymes or spontaneously reacted with another glutathione to produce hydrogen sulfide and glutathione disulfide. The new mechanism of zero-valent sulfur transfer as membrane lipid-soluble S₈ molecules is common among tested microorganisms and may also occur in the environment for microorganisms to share and use zero-valent sulfur.