Noll 9418197 This project is an investigation of the physiology of elemental sulfur reduction to sulfide by the hyperthromophilic bacterium Thermotoga neapolitana. Sulfur reduction (sulfidogenesis) is a common property of hyperthermophilic bacteria and archaea, but the mechanisms by which it occurs may differ among these organisms. Since sulfidogenesis is found in organisms similar to the common ancestors of two phylogenetic domains, it may have been present in the ancestors of all lining organisms and, thus, represents an early means to enhance catabolism using an inorganic electron acceptor. Our goals in this project are to determine how sulfidogenesis contributes to bioenergetics and to elucidate the metabolic pathways that lead to sulfide production. We intend to achieve these goals by pursuing three objectives. (1) We will purify and characterize an NADH:polysulfide oxidoreductase, one of two known sulfur reductases in T. neapolitiana. We will clone its gene to study its regulation and relationship to adjacent genes. (2) We will isolate mutants defective in key enzymatic activities to test hypotheses derived from biochemical studies and look for evidence of alternative bioenergetics pathways. (3) We will finally develop a cloning vector for T. neapolitiana for the long range goals of introducing mutations via gene replacement and examining catabolic regulation. %%% This project is a study of how solid elemental sulfur is converted to hydrogen sulfide gas by the bacterium Thermotoga neapolitana, an organism that grows at very high temperatures (a hyperthermophilic). Sulfide formation is a common property of hyperthermophilic organisms, but the mechanism by which it occurs is unknown for many of them. This process has evolutionary, ecological, and economic importance. Since the process is found in organisms thought to be like some of the fist organisms to appear on Earth, it may represent an early metabolic process. The sulfur cycle is central to t he biology of geothermal ecosystems, so these hyperthermophiles are important in these environments. The biological removal of sulfurous compounds from coals and ores has traditionally been mediated by aerobes. Hyperthermophilic anaerobes or their enzymes may provide an alternative means to solubilize bound sulfur for measurement or removal. Our goals in this project are to determine how sulfide formation contributes to bioenergetics and to elucidate the metabolic pathways that lead to sulfide production. We intend to achieve these goals by studying the enzymes that mediate this process, isolating the genes that encode these enzymes, and developing genetic tools that will allow future investigations of these enzymes, and developing genetic tools that will allow future investigations of these and other questions about the metabolism of this fascinating organism. ***
