Sulfide dehydrogenase from the hyperthermophilic archaeon Pyrococcus furiosus: a new multifunctional enzyme involved in the reduction of elemental sulfur

Abstract

Pyrococcus furiosus is an anaerobic archaeon that grows optimally at 1000C by the fermentation of carbohydrates yielding acetate, C02, and H2 as the primary products. If elemental sulfur (SO) or polysulfide is added to the growth medium, H2S is also produced. The cytoplasmic hydrogenase of P. furiosus, which is responsible for H2 production with ferredoxin as the electron donor, has been shown to also catalyze the reduction of polysulfide to H2S (K. Ma, R. N. Schicho (33). The majority are strict anaerobes, and most are obligately dependent upon the reduction of elemental sulfur (S) to H2S for optimal growth. Molecular H2 or organic compounds serve as electron donors for the apparent respiration of So. Some of the heterotrophic species are able to grow in the absence of S by fermentation-type metabolisms that result in the production of H2. In such cases, the addition of So to the growth medium leads to H2S production and growth stimulation. Since the hyperthermophiles are the most slowly evolving of known life forms, it has been suggested that S0 respiration may represent one of the earliest mechanisms of energy conservation from an evolutionary perspective (40, 47).The mechanisms by which hyperthermophilic organisms reduce So to H2S and the natures of the enzymes involved are far from clear. The situation is complicated by the fact that the abiotic reduction of S0 can also occur at the growth temperatures of these organisms (9). Also, because of the low solubility of S in aqueous media, golysulfide is thought to be the true substrate for microbial S reduction (9,40,41 nism of H2S production from S0 has been investigated in only one autotrophic hyperthermophile, Pyrodictium brockii, an obligate S-reducing species which grows optimally at 1050C. This organism was shown to have a primitive membrane-bound electron transport chain for coupling H2 oxidation and S0 reduction (36). The chain contained hydrogenase, a cytochrome, and a novel quinone, but the So-reducing entity was not purified. In fact, there have been few reports on S5 reduction by mesophilic organisms. For example, Zophel and coworkers screened several different So-reducing bacteria for sulfur oxidoreductase activity (50) and the enzyme responsible in "Spirillum" strain 5175 (44) was postulated to be an iron-sulfur protein possibly associated with a c-type cytochrome (51). However, only one S0-reducing enzyme has been purified and characterized from a mesophile, that from Wolinella succinogenes (20,21,43), an organism which grows with formate as the electron donor and S0 as the electron acceptor (27). From sequencing analysis, it was postulated that its polysulfide reductase is composed of three subunits and is a molybdopterin-containing iron-sulfur protein (21).We are investigating the So-reducing activities of heterotrophic hyperthermophiles such as P. furiosus (18). This obligate anaerobe grows optimally at 100'C by the fermentation of carbohydrates and peptides in which excess reductant, generated mainly in the form of reduced ferredoxin (2,5,30)...

Pyrococcus furiosus glyceraldehyde 3‐phosphate oxidoreductase has comparable W6+/5+ and W5+/4+ reduction potentials and unusual [4Fe‐4S] EPR properties

“…All g values are below 2.0, which is unusual. Similar EPR spectra have only been reported for putative [4Fe-4S] clusters in NADH-reduced glutamate synthase [21] and NADPH-reduced sul¢de dehydrogenase (ferredoxin NADPH oxidoreductase) [22]. As can be seen in the saturation plot (Fig.…”

Involvement of Geobacter sulfurreducens SfrAB in acetate metabolism rather than intracellular, respiration-linked Fe(III) citrate reduction

“…GSU3057 and GSU3058 were previously annotated as a homotetrameric NADPHdependent glutamate synthase and a putative dihydroorotate electron transfer subunit, respectively . However, no NADPH-dependent glutamate synthase activity could be detected in either wild-type or acetateadapted SfrAB-null extracts, and GSU3057 and GSU3058 were found to be 65.6 % and 65.2 % similar, respectively, to the a and b subunits of the NADPH-dependent ferredoxin oxidoreductase (FNOR) of Pyrococcus furiosus (Ma & Adams, 1994, 2001Schut et al, 2003). Phylogenetic analysis of GSU3057 and related proteins, including SfrB, which is 36 % similar, clearly indicated that GSU3057 was more closely related to the a subunit of P. furiosus FNOR than to the small subunits of the characterized glutamate synthases (Fig.…”

Anaerobic Elemental Sulfur Reduction by FungusFusarium oxysporum

“…Since S 8 is much less soluble and membranepermeable, it is thought that it is not directly reduced by bacteria, but is converted to a more soluble compound that serves as the actual substrate for reduction. [22][23][24] In the case of Wolinella succinogenes, polysulfide was found to be the soluble intermediate for sulfur reduction, and its polysulfide reductase was identified. 26) Polysulfide is generated chemically from S 8 and trace amounts of sulfide or polysulfide by the following reaction scheme: S n þ S m 2À !…”

“…To date, similar soluble NADH-dependent SRs have been found in Thiobacillus ferrooxidans 25) and Pyrococcus furiosus. 23) These organisms oxidize ferrous ion and organic acids respectively to generate ATP, and the resulting redox equivalent (NADH) was re-oxidized by the activity of SR. Similarly, fungal SR is thought to function in re-oxidizing NADH to NAD þ under O 2 -limited conditions.…”

“…[22][23][24] Hence we examined the reducing activity of more soluble polysulfide ( À S-S n -S À ) and colloidal sulfur (HS 8 S 2 O 3 À ) to H 2 S using fungal cell-free extract. The results showed that the NADH-dependent reducing activity for these substrates was 1.6-and 2.8-nmol min À1 mg À1 respectively (Fig.…”