Effects of elemental sulfur on the metabolism of the deep-sea hyperthermophilic archaeon Thermococcus strain ES-1: Characterization of a sulfur-regulated, non-heme iron alcohol dehydrogenase

Abstract

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°C by the fermentation of peptides and reduces elemental sulfur (S0) to H2S. It is shown here that the growth rates and cell yields of strain ES- 1 are dependent upon the concentration of S0 in the medium, and no growth was observed in the absence of S0. The activities of various catabolic enzymes in cells grown under conditions of sufficient and limiting S0 concentrations were investigated. These enzymes included alcohol dehydrogenase (ADH); formate benzyl viologen oxidoreductase; hydrogenase; glutamate dehydrogenase; alanine dehydrogenase; aldehyde ferredoxin (Fd) oxidoreductase; formaldehyde 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 grown under S0 limitation. This was accompanied by increased amounts of H2 and alcohol (ethanol and butanol) from cultures grown with limiting S0. 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 S0 limitation, ADH reduces to alcohols the aldehydes that are generated by fermentation, thereby serving to dispose of excess reductant.