Role of D-cysteine desulfhydrase in the adaptation of Escherichia coli to D-cysteine

D-Cysteine, a powerful inhibitor of Escherichia coli growth, is decomposed in vitro into pyruvate, H2S, and NH3 by D-cysteine desulfhydrase. To assess the role of this reaction in the adaptation of the bacterium to growth on D-cysteine, the gene of the desulfhydrase was cloned. It corresponds to the open reading frame yedO at 43.03 min on the genetic map of E. coli. The am ino acid sequence deduced from this gene is homologous to those of several 1-aminocyclopropane-carboxylate deaminases. However, the E. coli desulfhydr ase does not use 1-aminocyclopropane-1-carboxylate as substrate. Various mu tants in which the yedO gene was inactivated or overexpressed were construc ted. They exhibited hypersensitivity or resistance, respectively, to the pr esence of D-cysteine in the culture medium. Growth protection against D-cys teine in minimal medium was conferred by the simultaneous addition of isole ucine, leucine, and valine. In agreement with this behavior, D-cysteine inh ibited the activity of threonine deaminase, a key enzyme of the isoleucine, leucine, and valine pathway. Finally, in the presence of the intact yedO g ene, E. coli growth was improved by addition of D-cysteine as the sole sulf ur source. In agreement with a role of the desulfhydrase in sulfur metaboli sm, yedO expression was induced under conditions of sulfate limitation.