Project description:The study investigated the ability of selected (hyper-)thermophilic prokaryotes to grow anaerobically by the reduction of perchlorate and chlorate. Physiological, genomic and proteome analyses suggest that the Crenarchaeon Aeropyrum pernix reduces (per)chlorate with a periplasmic enzyme related to nitrate reductases, while it lacks a functional chlorite-disproportionating enzyme (Cld). A. pernix seems to rely on the chemical reactivity of reduced sulfur compounds with the toxic intermediate chlorite to complete the pathway. The chemical oxidation of thiosulfate (in excessive amounts present in the medium) to sulfate and the concomitant release of chloride anions from the reduction of chlorite are the products of a biotic-abiotic (per)chlorate reduction pathway in A. pernix. The apparent absence of Cld in two other (per)chlorate-reducing microorganisms and their dependence on sulfide for (per)chlorate reduction is consistent with earlier-made observations on (per)chlorate-reducing Archaeoglobus fulgidus. All here discussed microorganisms use strategies for complete (per)chlorate reduction that differ from the physiology of classical (per)chlorate-reducing mesophiles.
