Optimization of a Method for Detecting Intracellular Sulfane Sulfur Levels and Evaluation of Reagents That Affect the Levels in Escherichia coli

The Activity of YCA1 Metacaspase Is Regulated by Reactive Sulfane Sulfur via Persulfidation in Saccharomyces cerevisiae

YCA1, the only metacaspase in Saccharomyces cerevisiae, plays important roles in the regulation of chronological lifespan, apoptosis, and cytokinesis. YCA1 has protein hydrolase activity and functions by cleaving itself and target proteins. However, there are few reports about the regulation of YCA1 activity. In this study, we observed that reactive sulfane sulfur (RSS) can inhibit the activity of YCA1. In vitro experiments demonstrated that RSS reacted with the Cys276 of YCA1, the residue central to its protein hydrolase activity, to form a persulfidation modification (protein-SSH). This modification inhibited both its self-cleavage and the cleavage of its substrate protein, BIR1. To investigate further, we constructed a low-endogenous-RSS mutant of S. cerevisiae, BY4742 Δcys3, in which the RSS-producing enzyme cystathionine-γ-lyase (CYS3) was knocked out. The activity of YCA1 was significantly increased by the deletion of CYS3. Moreover, increased YCA1 activity led to reduced chronological lifespan (CLS) and CLS-driven apoptosis. This study unveils the first endogenous factor that regulates YCA1 activity, introduces a novel mechanism of how yeast cells regulate chronological lifespan, and broadens our understanding of the multifaceted roles played by RSS.

Microorganisms uptake zero-valent sulfur via membrane lipid dissolution of octasulfur and intracellular solubilization as persulfide

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.

The Rhodanese PspE Converts Thiosulfate to Cellular Sulfane Sulfur in Escherichia coli

Hydrogen sulfide (H₂S) and its oxidation product zero-valent sulfur (S⁰) play important roles in animals, plants, and bacteria. Inside cells, S⁰ exists in various forms, including polysulfide and persulfide, which are collectively referred to as sulfane sulfur. Due to the known health benefits, the donors of H₂S and sulfane sulfur have been developed and tested. Among them, thiosulfate is a known H₂S and sulfane sulfur donor. We have previously reported that thiosulfate is an effective sulfane sulfur donor in Escherichia coli; however, it is unclear how it converts thiosulfate to cellular sulfane sulfur. In this study, we showed that one of the various rhodaneses, PspE, in E. coli was responsible for the conversion. After the thiosulfate addition, the ΔpspE mutant did not increase cellular sulfane sulfur, but the wild type and the complemented strain ΔpspE::pspE increased cellular sulfane sulfur from about 92 μM to 220 μM and 355 μM, respectively. LC-MS analysis revealed a significant increase in glutathione persulfide (GSSH) in the wild type and the ΔpspE::pspE strain. The kinetic analysis supported that PspE was the most effective rhodanese in E. coli in converting thiosulfate to glutathione persulfide. The increased cellular sulfane sulfur alleviated the toxicity of hydrogen peroxide during E. coli growth. Although cellular thiols might reduce the increased cellular sulfane sulfur to H₂S, increased H₂S was not detected in the wild type. The finding that rhodanese is required to convert thiosulfate to cellular sulfane sulfur in E. coli may guide the use of thiosulfate as the donor of H₂S and sulfane sulfur in human and animal tests.

A sulfide-sensor and a sulfane sulfur-sensor collectively regulate sulfur-oxidation for feather degradation by Bacillus licheniformis

Bacillus licheniformis MW3 degrades bird feathers. Feather keratin is rich in cysteine, which is metabolized to produce hazardous sulfide and sulfane sulfur. A challenge to B. licheniformis MW3 growing on feathers is to detoxify them. Here we identified a gene cluster in B. licheniformis MW3 to deal with these toxicity. The cluster contains 11 genes: the first gene yrkD encodes a repressor, the 8^th and 9^th genes nreB and nreC encode a two-component regulatory system, and the 10th and 11th genes encode sulfide: quinone reductase (SQR) and persulfide oxygenase (PDO). SQR and PDO collectively oxidize sulfide and sulfane sulfur to sulfite. YrkD sensed sulfane sulfur to derepress the 11 genes. The NreBC system sensed sulfide and further amplified the transcription of sqr and pdo. The two regulatory systems synergistically controlled the expression of the gene cluster, which was required for the bacterium to grow on feather. The findings highlight the necessity of removing sulfide and sulfane sulfur during feather degradation and may help with bioremediation of feather waste and sulfide pollution.