Key role for sulfur in peptide metabolism and in regulation of three hydrogenases in the hyperthermophilic archaeon Pyrococcus furiosus

The hyperthermophilic archaeon Pyrococcus furiosus grows optimally at 100 d egreesC by the fermentation of peptides and carbohydrates. Growth of the or ganism was examined in media containing either maltose, peptides (hydrolyze d casein), or both as the carbon source(s), each with and without elemental sulfur (S-0). Growth rates were highest on media containing peptides and S -0, with or without maltose. Growth did not occur on the peptide medium wit hout S-0. S-0 had no effect on growth rates in the maltose medium in the ab sence of peptides. Phenylacetate production rates (from phenylalanine ferme ntation) from cells grown in the peptide medium containing S-0 with or with out maltose were the same, suggesting that S-0 is required for peptide util ization. The activities of 14 of 21 enzymes involved in or related to the f ermentation pathways of P. furiosus were shown to be regulated under the fi ve different growth conditions studied. The presence of S-0 in the growth m edia resulted in decreases in specific activities of two cytoplasmic hydrog enases (I and II) and of a membrane-bound hydrogenase, each by an order of magnitude. The primary S-0-reducing enzyme in this organism and the mechani sm of the S-0 dependence of peptide metabolism are not known. This study pr ovides the first evidence for a highly regulated fermentation-based metabol ism in P. furiosus and a significant regulatory role for elemental sulfur o r its metabolites.