Sugar utilization in the hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324: starch degradation to acetate and CO2 via a modified Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming)

The hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324, rather than the type strain VC16, was found to grow on starch and sulfate as energy and carbon source. Fermentation products and enzyme activities were determined in starch-grown cells and compared to those of cells grown on lactate and sulfate. During exponential growth on starch, 1 mol of glucose-equivalent was incompletely oxidized with sulfate to approximately 2 mol acetate, 2 mol CO2 and 1 mol H2S. Starch-grown cells did not contain measurable amounts of the deazaflavin factor F420 (<0.03 nmol/mg protein) and thus did not show the F420-specific green-blue fluorescence. In contrast, lactate (1 mol) was completely oxidized with sulfate to 3 mol CO2 by strain 7324, and lactate-grown cells contained high amounts of F420 (0.6 nmol/mg protein). In extracts of starch-grown cells, the following enzymes of a modified Embden-Meyerhof pathway were detected: ADP-dependent hexokinase (ADP-HK), phosphoglucose isomerase, ADP-dependent 6-phosphofructokinase (ADP-PFK), fructose-1,6-phosphate aldolase, glyceraldehyde-3-phosphate:ferredoxin oxidoreductase (GAP:FdOR), phosphoglycerate mutase, enolase, and pyruvate kinase (PK). Specific activities of ADP-HK, ADP-PFK, GAP:FdOR, and PK were significantly higher in starch-grown cells than in lactate-grown cells, indicating induction of these enzymes during starch catabolism. Pyruvate conversion to acetate involved pyruvate:ferredoxin oxidoreductase and ADP-forming acetyl-CoA synthetase. The findings indicate that the archaeal sulfate reducer A. fulgidus strain 7324 converts starch to acetate via a modified Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming). This is the first report of growth of a sulfate reducer on starch, i.e. on a polymeric sugar.     

Effect of low sulfate concentrations on lactate oxidation and isotope fractionation during sulfate reduction by Archaeoglobus fulgidus strain Z

The effect of low substrate concentrations on the metabolic pathway and sulfur isotope fractionation during sulfate reduction was investigated for Archaeoglobus fulgidus strain Z. This archaeon was grown in a chemostat with sulfate concentrations between 0.3 mM and 14 mM at 80 degrees C and with lactate as the limiting substrate. During sulfate reduction, lactate was oxidized to acetate, formate, and CO2. This is the first time that the production of formate has been reported for A. fulgidus. The stoichiometry of the catabolic reaction was strongly dependent on the sulfate concentration. At concentrations of more than 300 microM, 1 mol of sulfate was reduced during the consumption of 1 mol of lactate, whereas only 0.6 mol of sulfate was consumed per mol of lactate oxidized at a sulfate concentration of 300 microM. Furthermore, at low sulfate concentrations acetate was the main carbon product, in contrast to the CO2 produced at high concentrations. We suggest different pathways for lactate oxidation by A. fulgidus at high and low sulfate concentrations. At about 300 microM sulfate both the growth yield and the isotope fractionation were limited by sulfate, whereas the sulfate reduction rate was not limited by sulfate. We suggest that the cell channels more energy for sulfate uptake at sulfate concentrations below 300 to 400 microM than it does at higher concentrations. This could explain the shift in the metabolic pathway and the reduced growth yield and isotope fractionation at low sulfate levels.     

The Archaeoglobus fulgidus D-lactate dehydrogenase is a Zn(2+) flavoprotein

Archaeoglobus fulgidus, a hyperthermophilic, archaeal sulfate reducer, is one of the few organisms that can utilize D-lactate as a sole source for both carbon and electrons. The A. fulgidus open reading frame, AF0394, which is predicted to encode a D-(-)-lactate dehydrogenase (Dld), was cloned, and its product was expressed in Escherichia coli as a fusion with the maltose binding protein (MBP). The 90-kDa MBP-Dld fusion protein was more efficiently expressed in E. coli when coexpressed with the E. coli dnaY gene, encoding the arginyl tRNA for the codons AGA and AGG. When cleaved from the fusion protein by treatment with factor Xa, the recombinant Dld (rDld) has an apparent molecular mass of 50 kDa, similar to that of the native A. fulgidus Dld enzyme. Both the purified MBP-Dld fusion protein and its rDld cleavage fragment have lactate dehydrogenase activities specific for D-lactate, are stable at 80 degrees C, and retain activity after exposure to oxygen. The flavin cofactor FAD, which binds rDld apoprotein with a 1:1 stoichiometry, is essential for activity.     

Archaeoglobus fulgidus couples CO oxidation to sulfate reduction and acetogenesis with transient formate accumulation

The genome sequence of Archaeoglobus fulgidus VC16 encodes three CO dehydrogenase genes. Here we explore the capacity of A. fulgidus to use CO as growth substrate. Archaeoglobus fulgidus VC16 was successfully adapted to growth medium that contained sulfate and CO. In the presence of CO and sulfate the culture OD(660) increased to 0.41 and sulfide, carbon dioxide, acetate and formate were formed. Accumulation of formate was transient. Similar results, except that no sulfide was formed, were obtained when sulfate was omitted. Hydrogen was never detected. Under the conditions tested, the observed concentrations of acetate (18 mM) and formate (8.2 mM) were highest in cultures without sulfate. Proton NMR spectroscopy indicated that CO2, and not CO, is the precursor of formate and the methyl group of acetate. Methylviologen-dependent formate dehydrogenase activity (1.4 micromol formate oxidized min(-1) mg(-1)) was detected in cell-free extracts and expected to have a role in formate reuptake. It is speculated that formate formation proceeds through hydrolysis of formyl-methanofuran or formyl-tetrahydromethanopterin. This study demonstrates that A. fulgidus can grow chemolithoautotrophically with CO as acetogen, and is not strictly dependent on the presence of sulfate, thiosulfate or other sulfur compounds as electron acceptor.     

Genetic analysis of Carboxydothermus hydrogenoformans carbon monoxide dehydrogenase genes cooF and cooS

Carboxydothermus hydrogenoformans is an extremely thermophilic, Gram-positive bacterium growing on carbon monoxide (CO) as single carbon and energy source and producing only H(2) and CO(2). Carbon monoxide dehydrogenase is a key enzyme for CO metabolism. The carbon monoxide dehydrogenase genes cooF and cooS from C. hydrogenoformans were cloned and sequenced. These genes showed the highest similarity to the cooF genes from the archaeon Archaeoglobus fulgidus and the cooS gene from the bacterium Rhodospirillum rubrum, respectively. The cooS gene was identified immediately downstream of cooF, however, the cooF and cooS genes from C. hydrogenoformans have substantially different codon usage, and the cooF gene Arg codon usage pattern, dominated by AGA and AGG, resembles the archaeal pattern. The data therefore suggest lateral transfer of these genes, possibly from different donor species.     

Cellular localization of D-lactate dehydrogenase and NADH oxidase from Archaeoglobus fulgidus

Members of the genus Archaeoglobus are hyperthermophilic sulfate reducers with an optimal growth temperature of 83 degrees C. Archaeoglobus fulgidus can utilize simple compounds including D-lactate, L-lactate and pyruvate as the sole substrate for carbon and electrons for dissimilatory sulfate reduction. Previously we showed that this organism makes a D-lactate dehydrogenase (Dld) that requires FAD and Zn2+ for activity. To determine the cellular location and topology of Dld and to identify proteins that interact with Dld, an antibody directed against Dld was prepared. Immunocytochemical studies using gold particle-coated secondary antibodies show that more than 85% of Dld is associated with the membrane. A truncated form of Dld was detected in immunoblots of whole cells treated with protease, showing that Dld is an integral membrane protein and that a significant portion of Dld, including part of the FAD-binding pocket, is outside the membrane facing the S-layer. The gene encoding Dld is part of an operon that includes noxA2, which encodes one of several NADH oxidases in A. fulgidus. Previous studies have shown that NoxA2 remains bound to Dld during purification. Thin sections of A. fulgidus probed simultaneously with antibodies against Dld and NoxA2 show that both proteins co-localized to the same sites in the membrane. Although these data show a tight interaction between NoxA2 and Dld, the role of NoxA2 in electron transport reactions is unknown. Rather, NoxA2 may protect proteins involved in electron transfer by reducing O2 to H2O2 or H2O.     

Structural characteristics of methanogenic cofactors in the non-methanogenic archaebacterium Archaeoglobus fulgidus

Archaeoglobus fulgidus is an extremely thermophilic, sulphate reducing archaebacterium thought to represent a biochemical missing-link between sulphur-metabolizing bacteria and methanogenic bacteria. Whereas the phylogenetic position of A.fulgidus is closer to the sulphur-metabolizing bacteria, there is a partial overlap in the biochemical machinery of A.fulgidus with both groups of bacteria. In particular, the presence of a number of aberrant cofactors up to now thought to be involved exclusively in the process of methanogenesis in methanogenic archaebacteria, i.e. coenzyme F420, methanofuran and methanopterin, has been indicated by previous studies. Here we present evidence for the structural identity of the methanopterin cofactor of A.fulgidus with the methanopterin isolated from Methanobacterium thermoautotrophicum and show that this non-methanogenic bacterium contains two as yet unknown analogues of coenzyme F420. The levels of the various cofactors were determined in cultures grown either on formate or lactate as the carbon source and sulphate or thiosulphate as the sulphur source.     

Distribution of thermophilic marine sulfate reducers in north sea oil field waters and oil reservoirs

The distribution of thermophilic marine sulfate reducers in produced oil reservoir waters from the Gullfaks oil field in the Norwegian sector of the North Sea was investigated by using enrichment cultures and genus-specific fluorescent antibodies produced against the genera Archaeoglobus, Desulfotomaculum, and Thermodesulforhabdus. The thermophilic marine sulfate reducers in this environment could mainly be classified as species belonging to the genera Archaeoglobus and Thermodesulforhabdus. In addition, some unidentified sulfate reducers were present. Culturable thermophilic Desulfotomaculum strains were not detected. Specific strains of thermophilic sulfate reducers inhabited different parts of the oil reservoir. No correlation between the duration of seawater injection and the numbers of thermophilic sulfate reducers in the produced waters was observed. Neither was there any correlation between the concentration of hydrogen sulfide and the numbers of thermophilic sulfate reducers. The results indicate that thermophilic and hyperthermophilic sulfate reducers are indigenous to North Sea oil field reservoirs and that they belong to a deep subterranean biosphere.     

Structure of the F420H2:quinone oxidoreductase of Archaeoglobus fulgidus identification and overproduction of the F420H2-oxidizing subunit.

The F420H2:quinone oxidoreductase from the sulfate-reducing archaeon Archaeoglobus fulgidus is encoded by the fqo gene cluster which comprises 11 genes (fqo J, K, M, L, N, A, BC, D, H, I, F). The last gene of the cluster, fqoF, was overexpressed in Escherichia coli. The purified subunit was able to oxidize reduced cofactor F420 using the electron-acceptor system methyl viologen plus metronidazole. The specific activity at 78 degrees C was 64 micromol F420H2 oxidized. min-1.(mg protein)-1. The purified polypeptide contained 10.6 mol non-heme iron, 7.2 mol acid-labile sulfur and 0.7 mol FAD per mol protein. With the exception of fqoF, the deduced amino-acid sequences of all other genes show homologies to distinct subunits of NADH-quinone oxidoreductases from prokaryotes and eukaryotes. Thus, it is concluded that the F420H2-dependent and the NADH-dependent enzyme are functional equivalents. Both proteins are the initial enzymes of membrane-bound electron-transport systems and are involved in energy conservation. In parallel with bacterial complex I, the F420H2:quinone oxidoreductase may be composed of three subcomplexes. FqoF functions as the input device adjusted to the oxidation of reduced cofactor F420H2, thereby replacing subunits of the input module of complex I that are not present in A. fulgidus. The subunits FqoB, FqoCD and FqoI may form the membrane-associated module and transfer electrons to the membrane-integral module. It is most likely that the last subcomplex is composed of FqoA, FqoH, FqoJ, FqoK, FqoL, FqoM and FqoN. All subunits are highly hydrophobic and are probably involved in the reduction of a special menaquinone with a fully reduced isoprenoid side chain present in the cytoplasmic membrane of A. fulgidus.     

Desulfobulbus mediterraneus sp. nov., a sulfate-reducing bacterium growing on mono- and disaccharides

A new sulfate-reducing bacterium, strain 86FS1, was isolated from a deep-sea sediment in the western Mediterranean Sea with sodium lactate as electron and carbon source. Cells were ovoid, gram-negative and motile. Strain 86FS1 contained b- and c-type cytochromes. The organism was able to utilize propionate, pyruvate, lactate, succinate, fumarate, malate, alanine, primary alcohols (C(2)-C(5)), and mono- and disaccharides (glucose, fructose, galactose, ribose, sucrose, cellobiose, lactose) as electron donors for the reduction of sulfate, sulfite or thiosulfate. The major products of carbon metabolism were acetate and CO(2), with exception of n-butanol and n-pentanol, which were oxidized only to the corresponding fatty acids. The growth yield with sulfate and glucose or lactate was 8.3 and 15 g dry mass, respectively, per mol sulfate. The temperature limits for growth were 10 degrees C and 30 degrees C with an optimum at 25 degrees C. Growth was observed at salinities ranging from 10 to 70 g NaCl l(-1). Sulfide concentrations above 4 mmol l(-1) inhibited growth. The fatty acid pattern of strain 86FS1 resembled that of Desulfobulbus propionicus with n-14:0, n-16:1omega7, n-16:1 omega5, n-17:1 omega6 and n-18:1 omega7 as dominant fatty acids. On the basis of its phylogenetic position and its phenotypic properties, strain 86FS1 affiliates with the genus Desulfobulbus and is described as a new species, Desulfobulbus mediterraneus sp. nov.     

Comparative analysis of pyruvate kinases from the hyperthermophilic archaea Archaeoglobus fulgidus,Aeropyrum pernix,and Pyrobaculum aerophilum and the hyperthermophilic bacterium Thermotoga maritima: unusual regulatory properties in hyperthermophilic archaea

Pyruvate kinases (PK, EC 2.7.1.40) from three hyperthermophilic archaea (Archaeoglobus fulgidus strain 7324, Aeropyrum pernix, and Pyrobaculum aerophilum) and from the hyperthermophilic bacterium Thermotoga maritima were compared with respect to their thermophilic, kinetic, and regulatory properties. PKs from the archaea are 200-kDa homotetramers composed of 50-kDa subunits. The enzymes required divalent cations, Mg2+ and Mn2+ being most effective, but were independent of K+. Temperature optima for activity were 85 degrees C (A. fulgidus) and above 98 degrees C (A. pernix and P. aerophilum). The PKs were highly thermostable up to 110 degrees C (A. pernix) and showed melting temperatures for thermal unfolding at 93 degrees C (A. fulgidus) or above 98 degrees C (A. pernix and P. aerophilum). All archaeal PKs exhibited sigmoidal saturation kinetics with phosphoenolpyruvate (PEP) and ADP indicating positive homotropic cooperative response with both substrates. Classic heterotropic allosteric regulators of PKs from eukarya and bacteria, e.g. fructose 1,6-bisphosphate or AMP, did not affect PK activity of hyperthermophilic archaea, suggesting the absence of heterotropic allosteric regulation. PK from the bacterium T. maritima is also a homotetramer of 50-kDa subunits. The enzyme was independent of K+ ions, had a temperature optimum of 80 degrees C, was highly thermostable up to 90 degrees C, and had a melting temperature above 98 degrees C. The enzyme showed cooperative response to PEP and ADP. In contrast to its archaeal counterparts, the T. maritima enzyme exhibited the classic allosteric response to the activator AMP and to the inhibitor ATP. Sequences of hyperthermophilic PKs showed significant similarity to characterized PKs from bacteria and eukarya. Phylogenetic analysis of PK sequences of all three domains indicates a distinct archaeal cluster that includes the PK from the hyperthermophilic bacterium T. maritima.     

Function of methanofuran,tetrahydromethanopterin, and coenzyme F420 in Archaeoglobus fulgidus

Archaeoglobus fulgidus is an extremely thermophilic archaebacterium that can grow at the expense of lactate oxidation with sulfate to CO₂ and H₂S. The organism contains coenzyme F₄₂₀, tetrahydromethanopterin, and methanofuran which are coenzymes previously thought to be unique for methanogenic bacteria. We report here that the bacterium contains methylenetetrahydromethanopterin: F₄₂₀ oxidoreductase (20 U/mg), methenyltetrahydromethanopterin cyclohydrolase (0.9 U/mg), formyltetrahydromethanopterin: methanofuran formyltransferase (4.4 U/mg), and formylmethanofuran: benzyl viologen oxidoreductase (35 mU/mg). Besides these enzymes carbon monoxide: methyl viologen oxidoreductase (5 U/mg), pyruvate: methyl viologen oxidoreductase (0.7 U/mg), and membranebound lactate: dimethylnaphthoquinone oxidoreductase (0.1 U/mg) were found. 2-Oxoglutarate dehydrogenase, which is a key enzyme of the citric acid cycle, was not detectable. From the enzyme outfit it is concluded that in A. fulgidus lactate is oxidized to CO₂ via a modified acetyl-CoA/carbon monoxide dehydrogenase pathway involving C₁-intermediates otherwise only used by methanogenic bacteria.Non-standard abbreviations APS adenosine 5-phosphosulfate - BV benzyl viologen - DCPIP 2,6-dichlorophenolindophenol - DMN 2,3-dimethyl-1,4-naphthoquinone - DTT DL-1,4-dithiothreitol - H₄F tetrahydrofolate - H₄MPT tetrahydromethanopterin - CH₂ H₄MPT, methylene-H₄MPT - CH H₄MPT, methenyl-H₄MPT - Mes morpholinoethane sulfonic acid - MFR methanofuran - Mops morpholinopropane sulfonic acid - MV methyl viologen - Tricine N-tris(hydroxymethyl)-methylglycine - U mol product formed per min     

Methanococcus jannaschii coenzyme F420 analogs contain a terminal alpha-linked glutamate

Analyses of the F(420)s present in Methanococcus jannaschii have shown that these cells contain a series of gamma-glutamyl-linked F(420)s capped with a single, terminal alpha-linked L-glutamate. The predominant form of F(420) was designated as alpha-F(420)-3 and represented 86% of the F(420)s in these cells. Analyses of Methanosarcina thermophila, Methanosarcina barkeri, Methanobacterium thermoautotrophicum, Archaeoglobus fulgidus, and Mycobacterium smegmatis showed that they contained only gamma-glutamyl-linked F(420)s.     

A novel archaeal alanine dehydrogenase homologous to ornithine cyclodeaminase and mu-crystallin

A novel alanine dehydrogenase (AlaDH) showing no significant amino acid sequence homology with previously known bacterial AlaDHs was purified to homogeneity from the soluble fraction of the hyperthermophilic archaeon Archaeoglobus fulgidus. AlaDH catalyzed the reversible, NAD+-dependent deamination of L-alanine to pyruvate and NH4+. NADP(H) did not serve as a coenzyme. The enzyme is a homodimer of 35 kDa per subunit. The Km values for L-alanine, NAD+, pyruvate, NADH, and NH4+ were estimated at 0.71, 0.60, 0.16, 0.02, and 17.3 mM, respectively. The A. fulgidus enzyme exhibited its highest activity at about 82 degrees C (203 U/mg for reductive amination of pyruvate) yet still retained 30% of its maximum activity at 25 degrees C. The thermostability of A. fulgidus AlaDH was increased by more than 10-fold by 1.5 M KCl to a half-life of 55 h at 90 degrees C. At 25 degrees C in the presence of this salt solution, the enzyme was approximately 100% stable for more than 3 months. Closely related A. fulgidus AlaDH homologues were found in other archaea. On the basis of its amino acid sequence, A. fulgidus AlaDH is a member of the ornithine cyclodeaminase-mu-crystallin family of enzymes. Similar to the mu-crystallins, A. fulgidus AlaDH did not exhibit any ornithine cyclodeaminase activity. The recombinant human mu-crystallin was assayed for AlaDH activity, but no activity was detected. The novel A. fulgidus gene encoding AlaDH, AF1665, is designated ala.     

Unusual starch degradation pathway via cyclodextrins in the hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324

The hyperthermophilic archaeon Archaeoglobus fulgidus strain 7324 has been shown to grow on starch and sulfate and thus represents the first sulfate reducer able to degrade polymeric sugars. The enzymes involved in starch degradation to glucose 6-phosphate were studied. In extracts of starch-grown cells the activities of the classical starch degradation enzymes, alpha-amylase and amylopullulanase, could not be detected. Instead, evidence is presented here that A. fulgidus utilizes an unusual pathway of starch degradation involving cyclodextrins as intermediates. The pathway comprises the combined action of an extracellular cyclodextrin glucanotransferase (CGTase) converting starch to cyclodextrins and the intracellular conversion of cyclodextrins to glucose 6-phosphate via cyclodextrinase (CDase), maltodextrin phosphorylase (Mal-P), and phosphoglucomutase (PGM). These enzymes, which are all induced after growth on starch, were characterized. CGTase catalyzed the conversion of starch to mainly beta-cyclodextrin. The gene encoding CGTase was cloned and sequenced and showed highest similarity to a glucanotransferase from Thermococcus litoralis. After transport of the cyclodextrins into the cell by a transport system to be defined, these molecules are linearized via a CDase, catalyzing exclusively the ring opening of the cyclodextrins to the respective maltooligodextrins. These are degraded by a Mal-P to glucose 1-phosphate. Finally, PGM catalyzes the conversion of glucose 1-phosphate to glucose 6-phosphate, which is further degraded to pyruvate via the modified Embden-Meyerhof pathway.     

Properties of lactate dehydrogenase in a psychrophilic marine bacterium

Lactate dehydrogenase (EC 1.1.1.27) from Vibrio marinus MP-1 was purified 15-fold and ammonium activated. The optimum pH for pyruvate reduction was 7.4. Maximum lactate dehydrogenase activity occurred at 10 to 15 degrees C, and none occurred at 40 degrees C. The crude-extract enzyme was stable between 15 and 20 degrees C and lost 50% of its activity after 60 min at 45 degrees C. The partially purified enzyme was stable between 8 and 15 degrees C and lost 50% of its activity after 60 min at 30 degrees C. The thermal stability of lactate dehydrogenase was increased by mercaptoethanol, with 50% remaining activity at 42 degrees C.     

Properties of Lactate Dehydrogenase in a Psychrophilic Marine Bacterium

Lactate dehydrogenase (EC 1.1.1.27) from Vibrio marinus MP-1 was purified 15-fold and ammonium activated. The optimum pH for pyruvate reduction was 7.4. Maximum lactate dehydrogenase activity occurred at 10 to 15 degrees C, and none occurred at 40 degrees C. The crude-extract enzyme was stable between 15 and 20 degrees C and lost 50% of its activity after 60 min at 45 degrees C. The partially purified enzyme was stable between 8 and 15 degrees C and lost 50% of its activity after 60 min at 30 degrees C. The thermal stability of lactate dehydrogenase was increased by mercaptoethanol, with 50% remaining activity at 42 degrees C.     

Spore-forming thermophilic sulfate-reducing bacteria isolated from north sea oil field waters

Thermophilic sulfate-reducing bacteria were isolated from oil field waters from oil production platforms in the Norwegian sector of the North Sea. Spore-forming rods dominated in the enrichments when lactate, propionate, butyrate, or a mixture of aliphatic fatty acids (C(4) through C(6)) was added as a carbon source and electron donor. Representative strains were isolated and characterized. The isolates grew autotrophically on H(2)-CO(2) and heterotrophically on fatty acids such as formate, propionate, butyrate, caproate, valerate, pyruvate, and lactate and on alcohols such as methanol, ethanol, and propanol. Sulfate, sulfite, and thiosulfate but not nitrate could be used as an electron acceptor. The temperature range for growth was 43 to 78 degrees C; the spores were extremely heat resistant and survived 131 degrees C for 20 min. The optimum pH was 7.0. The isolates grew well in salt concentrations ranging from 0 to 800 mmol of NaCl per liter. Sulfite reductase P582 was present, but cytochrome c and desulfoviridin were not found. Electron micrographs revealed a gram-positive cell organization. The isolates were classified as a Desulfotomaculum sp. on the basis of spore formation, general physiological characteristics, and submicroscopic organization. To detect thermophilic spore-forming sulfate-reducing bacteria in oil field water, polyvalent antisera raised against antigens from two isolates were used. These bacteria were shown to be widespread in oil field water from different platforms. The origin of thermophilic sulfate-reducing bacteria in the pore water of oil reservoirs is discussed.     

High-temperature microbial sulfate reduction can be accompanied by magnetite formation

The hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus was found to be capable of lithoautotrophic growth on medium containing molecular hydrogen, sulfate, and amorphous Fe(III) oxide. During the growth of this microorganism, amorphous Fe(III) oxide was transformed into black strongly magnetic sediment rich in magnetite, as shown by Mossbauer studies. Experiments involving inhibition of microbial sulfate reduction and abiotic controls revealed that magnetite production resulted from chemical reactions proceeding at elevated temperatures (83 degrees C) between molecular hydrogen, amorphous Fe(III) oxide, and sulfide formed enzymatically in the course of dissimilatory sulfate reduction. It follows that magnetite production in this system can be characterized as biologically mediated mineralization. This is the first report of magnetite formation as a result of activity of sulfate-reducing microorganisms.     

Isolation of saccharolytic dissimilatory sulfate-reducing bacteria

Abstract Four unidentified saccharolytic dissimilatory sulfate-reducing strains were isolated from an anaerobic digester. Cells were Gram-negative, motile, nonsporulating rods which differ markedly from known sulfate reducers especially with respect to carbon source utilisation and sulfur sources which can be reduced. The strains were capable of metabolising at least 26 out of 50 carbohydrates tested. Carbohydrates were, in the absence of exogenous sulfate, fermented to acetate, ethanol, lactate, carbon dioxide and hydrogen. In the presence of excess sulfate carbohydrates were fermented to acetate, ethanol, carbon dioxide, hydrogen and hydrogen sulfide, but lactate was not detected. An oxidized organic or inorganic sulfur source, including elemental sulfur, was not required as a prerequisite for growth on carbohydrates, Lactate was, in the presence of sulfate, converted to acetate, ethanol, carbon dioxide, hydrogen and hydrogen sulfide. In the absence of sulfate no lactate was utilised and no growth was observed.