Generation of hydrogen sulfide from sulfur assimilation in Escherichia coli.

Many organisms produce endogenous hydrogen sulfide (HS) as a by-product of protein, peptide, or L-cysteine degradation. Recent reports concerning mammalian cells have demonstrated that HS acts as a signaling molecule playing important roles in various biological processes. In contrast to mammals, bacterial HS signaling remains unclear. In this work, we demonstrate that Escherichia coli generates HS 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 HS generation. We found that HS 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 HS in a CRP-dependent manner as a response to glucose starvation. These results indicate that CRP plays a key role in the generation of HS coupled to thiosulfate assimilation, whose molecular mechanisms remains to be elucidated. Here, we propose a potential biological role of the HS as a signaling mediator for a cross-talk between carbon and sulfur metabolism in E. coli.