EFFECTS OF ELEMENTAL SULFUR ON THE METABOLISM OF THE DEEP-SEA HYPERTHERMOPHILIC ARCHAEON THERMOCOCCUS STRAIN ES-1 - CHARACTERIZATION OF A SULFUR-REGULATED, NONHEME IRON ALCOHOL-DEHYDROGENASE

The strictly anaerobic archaeon Thermococcus strain ES-1 was recently isolated from near a deep-sea hydrothermal vent. It grows at temperatures up to 91 degrees C by the fermentation of peptides and reduces elemental sulfur (S-0) to H2S. It is shown here that the growth rates and cell yields of strain ES-1 are dependent upon the concentration of S-0 in the medium, and no growth was observed in the absence of S-0. The activities of various catabolic enzymes in cells grown under conditions of sufficient and limiting S-0 concentrations were investigated. These enzymes included alcohol dehydrogenase (ADH); formate benzyl viologen oxidoreductase; hydrogenase; glutamate dehydrogenase; alanine dehydrogenase; aldehyde ferredoxin (Fd) oxidoreductase; formal-dehyde Fd oxidoreductase; and coenzyme A-dependent, Fd-linked oxidoreductases specific for pyruvate, indolepyruvate, 2-ketoglutarate, and 2-ketoisovalerate. Of these, changes were observed only with ADH, formate benzyl viologen oxidoreductase, and hydrogenase, the specific activities of which all dramatically increased in cells under S-0 limitation. This was accompanied by increased amounts of H-2 and alcohol (ethanol and butanol) from cultures grown with limiting S-0. Such cells were used to purify ADH to electrophoretic homogeneity. ADH is a homotetramer with a subunit M(r) of 46,000 and contains 1 g-atom of Fe per subunit, which, as determined by electron paramagnetic resonance analyses, is present as a mixture of ferrous and ferric forms. No other metals or acid-labile sulfide was detected by colorimetric and elemental analyses. ADH utilized NADP(H) as a cofactor and preferentially catalyzed aldehyde reduction. It is proposed that, under S-0 limitation, ADH reduces to alcohols the aldehydes that are generated by fermentation, thereby serving to dispose of excess reductant.