Hydrogen Sulfide: A Toxic Gas Produced by Dissimilatory Sulfate and Sulfur Reduction and Consumed by Microbial Oxidation - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 240

incomplete oxidation of organic electron donors has been reported for sulfur-
reducing eubacteria.
The sulfur reductase (SR) (EC 1.12.98.4-sulfhydrogenase, formerly EC
1.97.1.3-sulfur reductase) is a constitutive enzyme in sulfur-reducing eubacteria:
Desulfuromonas ( Drm. ) acetoxidans , Wolinella ( W. ) succinogenes , Sulfuros-
pirillum ( S. ) deleyianum , Desulfomicrobium ( Dsm .), and Desulfovibrio ( D. ) species
[ 26 , 27 ]. From genome organization, it appears that a multisubunit polysulfide
reductase (PSR) (

ʱ , ʲ , and ʳ ) is found in 8 Bacteria genera and 3 Archaea

genera [ 25 ].

1.1.2.2 Archaeal Sulfur Reduction

Many genera of Archaea are able to grow with elemental sulfur as terminal electron
acceptor in the energy metabolism [ 40 ]. The dissimilatory reduction of elemental
sulfur to hydrogen sulfide is linked with energy conservation as evidenced by
growth on H 2 and S 0 (E 0' S 0 /SH ¼ 270 mV) [ 41 ]. SR is also a constitutive

enzyme in the Archaea: Methanosarcina ( Ms. ) barkeri 227, Methanococcus
thermolithotrophicus , and Methanobacterium thermoautotrophicum Marburg [ 30 ].
All archaeal sulfur reducers are extremely thermophilic, whereas sulfur-
reducing eubacteria may be mesophilic or moderately thermophilic. The reduction
of S 0 is widespread among members of the Archaea, including deep-branching
hyperthermophilic genera. In the Euryarchaeota , sulfur reduction is present in the
orders Thermoplasmatales , Thermococcales , and many methanogens; in the
Crenarchaeota , sulfur reduction is found in the orders Desulfurococcales ,
Sulfolobales , and Thermoproteales [ 29 , 30 ].
Four mechanisms of S 0 reduction are known in Archaea: (a) The most wide-
spread metabolism consists in the facultative or obligate chemolitho-autotrophic
reduction of S 0 with H 2 , accomplished by many hyperthermophiles from the
Crenarchaeota , including members of the genera Thermoproteus , Sulfolobus ,
Stygiolobus , Pyrobaculum , Ignicoccus , Acidianus, Thermoplasma (Table 1 )[ 28 ,
30 ]. (b) Some members of the Archaea including representatives from the genera
Thermococcus, Thermodiscus, Hyperthermus, Stetteria, Thermocladium ,
Pyrodictium , Pyrococcus , and Desulfurococcus utilize S 0 reduction as a H 2 sink
during fermentative metabolism (Table 1 )[ 29 , 30 ]. (c) Some members of the order
Thermoproteales, and Pyrobaculum ( Pyb. ) islandicum , can respire heterotrophi-
cally with S 0 in an apparently energy-gaining metabolism [ 30 , 42 ]. (d) Some
hydrogen-oxidizing methanogenic Archaea like Methanococcus , Methanosarcina ,
Methanobacterium , Methanothermus, and Methanopyrus can also reduce S 0 with
H 2 or methanol [ 43 ].