Generation of hydrogen sulfide from sulfur assimilation in Escherichia coli

Many organisms produce endogenous hydrogen sulfide (H₂S) as a by-product of protein, peptide, or L-cysteine degradation. Recent reports concerning mammalian cells have demonstrated that H₂S acts as a signaling molecule playing important roles in various biological processes. In contrast to mammals, bacterial H₂S signaling remains unclear. In this work, we demonstrate that Escherichia coli generates H₂S through the assimilation of inorganic sulfur, without L-cysteine degradation. Comparison of phenotypes and genomes between laboratory E. coli K-12 strains revealed a major contribution of CRP (a protein that controls the expression of numerous genes involved in glycolysis) to H₂S generation. We found that H₂S was produced by cells growing in a synthetic minimal medium containing thiosulfate as a sole inorganic sulfur source, but not in a medium only containing sulfate. Furthermore, E. coli generated H₂S in a CRP-dependent manner as a response to glucose starvation. These results indicate that CRP plays a key role in the generation of H₂S coupled to thiosulfate assimilation, whose molecular mechanisms remains to be elucidated. Here, we propose a potential biological role of the H₂S as a signaling mediator for a cross-talk between carbon and sulfur metabolism in E. coli.