Characterization of a new periplasmic single-domain rhodanese encoded by a sulfur-regulated gene in a hyperthermophilic bacterium Aquifex aeolicus

Rhodaneses (thiosulfate cyanide sulfurtransferases) are enzymes involved in the production of the sulfur in sulfane form, which has been suggested to be the relevant biologically active sulfur species. Rhodanese domains occur in the three major domains of life. We have characterized a new periplasmic single-domain rhodanese from a hyperthermophile bacterium, Aquifex aeolicus, with thiosulfate:cyanide transferase activity, Aq-1599. The oligomeric organization of the enzyme is stabilized by a disulfide bridge. To date this is the first characterization from a hyperthermophilic bacterium of a periplasmic sulfurtransferase with a disulfide bridge. The aq-1599 gene belongs to an operon that also contains a gene for a prepilin peptidase and that is up-regulated when sulfur is used as electron acceptor. Finally, we have observed a sulfur-dependent bacterial adherence linked to an absence of flagellin suggesting a possible role for sulfur detection by A. aeolicus.