Cytochromes <Emphasis Type="Italic">c</Emphasis> of the anaerobic methacrylate reducer <Emphasis Type="Italic">Geobacter sulfurreducens</Emphasis> AM-1

Cytochromes c were found in the cells of the bacterium Geobacter sulfurreducens AM-1 grown on acetate and methacrylate. The periplasmic extract of G. sulfurreducens AM-1 contained about 88% of the total content of cytochromes c of intact cells. The analysis of cytochromes c from the native cells of G. sulfurreducens AM-1, from the periplasmic extract and from the cells treated by an alkaline solution showed the presence of nine proteins containing heme c. The molecular masses of cytochromes c from G. sulfurreducens AM-1 were 12.5, 15.5, 25.7, 29.5, 34.7, 41.7, 50.1, 63.1, and 67.6 kDa; localization of each cytochrome c was determined. Three heme-containing proteins (15.5 kDa, 25.7 kDa, and 29.5 kDa with the most intensive staining) were present mainly in the periplasm of the bacterium. The other two (50.1 and 67.6 kDa) were supposedly localized in the cell membrane. Cytochromes c with the molecular masses of 12.5, 15.5, and 67.6 kDa are considered as possible components of the methacrylate redox system of G. sulfurreducens AM-1.     

Unsaturated organic acids as terminal electron acceptors for reductase chains of anaerobic bacteria

This paper summarizes the current knowledge of unsaturated organic acids in their role as terminal electron acceptors of anaerobic bacteria. The mechanisms and enzyme systems involved in the reduction of fumarate by Escherichia coli, Wolinella succinogenes, and some species of the genus Shewanella are considered. Particular attention is given to reduction of the double bond of the unnatural compound methacrylate by the sigma-proteobacterium Geobacter sulfurreducens Am-1. Soluble periplasmic flavocytochromes c, found in bacteria of the genera Shewanella and Geobacter, are involved in the hydration of fumarate (in Shewanella species) and methacrylate (in G. sulfurreducens Am-1). In E. coli and W. succinogenes, fumarate is reduced in cytosol by membrane-bound fumarate reductases. The prospects for research into organic acid reduction at double bonds in bacteria are discussed.     

Recent Origin of the Methacrylate Redox System in Geobacter sulfurreducens AM-1 through Horizontal Gene Transfer

The origin and evolution of novel biochemical functions remains one of the key questions in molecular evolution. We study recently emerged methacrylate reductase function that is thought to have emerged in the last century and reported in Geobacter sulfurreducens strain AM-1. We report the sequence and study the evolution of the operon coding for the flavin-containing methacrylate reductase (Mrd) and tetraheme cytochrome с (Mcc) in the genome of G. sulfurreducens AM-1. Different types of signal peptides in functionally interlinked proteins Mrd and Mcc suggest a possible complex mechanism of biogenesis for chromoproteids of the methacrylate redox system. The homologs of the Mrd and Mcc sequence found in δ-Proteobacteria and Deferribacteres are also organized into an operon and their phylogenetic distribution suggested that these two genes tend to be horizontally transferred together. Specifically, the mrd and mcc genes from G. sulfurreducens AM-1 are not monophyletic with any of the homologs found in other Geobacter genomes. The acquisition of methacrylate reductase function by G. sulfurreducens AM-1 appears linked to a horizontal gene transfer event. However, the new function of the products of mrd and mcc may have evolved either prior or subsequent to their acquisition by G. sulfurreducens AM-1.     

Regulation of anaerobic respiratory pathways in Wolinella succinogenes by the presence of electron acceptors

In Wolinella succinogenes ATP synthesis and consequently bacterial growth can be driven by the reduction of either nitrate (E₀=+0.42 V), nitrite (E₀=+0.36 V), fumarate (E₀=+0.03 V) or sulphur (E₀=-0.27 V) with formate as the electron donor. Bacteria growing in the presence of nitrate and fumarate were found to reduce both acceptors simultaneously, while the reduction of both nitrate and fumarate is blocked during growth with sulphur. These observations were paralleled by the presence and absence of the corresponding bacterial reductase activities. Using a specific antiserum, fumarate reductase was shown to be present in bacteria grown with fumarate and nitrate, and to be nearly absent from bacteria grown in the presence of sulphur. The contents of polysulphide reductase, too, corresponded to the enzyme activities found in the bacteria. This suggests that the activities of anaerobic respiration are regulated at the biosynthetic level in W. succinogenes. Thus nitrate and fumarate reduction are repressed by the most electronegative acceptor of anacrobic respiration, sulphur. By contrast, in Escherichia coli a similar effect is exerted by the most electropositive acceptor, O₂. W. succinogenes also differs from E. coli in that fumarate reductase is not repressed by nitrate.Abbreviations BV benzyl viologen - DMN 2,3-dimethyl-1,4-naphthoquinone - DMSO dimethylsulfoxide - TMAO trimethylamine-N-oxide     

Phorphorylative electron transport chains lacking a cytochromebc 1 complex

Electron transport-coupled phosphorylation with fumarate as terminal acceptor inWolinella succinogenes yields less than 1 ATP/2 electrons. The generated by the electron transport is 0.18V and the H⁺/electron ratio is 1. The electron transport chain is made up of two dehydrogenases (hydrogenase and formate dehydrogenase) that catalyze the reduction of menaquinone, and fumarate reductase which catalyzes the oxidation of menaquinol.C-type cytochromes are not involved. The phosphorylative electron transport with sulfur as terminal acceptor inW. succinogenes orDesulfuromonas acetoxidans does not involve known quinones. The ATP yields should be even smaller than those with fumarate. Succinate oxidation by sulfur, which is a catabolic reaction inD. acetoxidans, is accomplished by reversed electron transport.     

A Periplasmic and Extracellular c-Type Cytochrome of Geobacter sulfurreducens Acts as a Ferric Iron Reductase and as an Electron Carrier to Other Acceptors or to Partner Bacteria

An extracellular electron carrier excreted into the growth medium by cells of Geobacter sulfurreducens was identified as a c-type cytochrome. The cytochrome was found to be distributed in about equal amounts in the membrane fraction, the periplasmic space, and the surrounding medium during all phases of growth with acetate plus fumarate. It was isolated from periplasmic preparations and purified to homogeneity by cation-exchange chromatography, gel filtration, and hydrophobic interaction chromatography. The electrophoretically homogeneous cytochrome had a molecular mass of 9.57 ± 0.02 kDa and exhibited in its reduced state absorption maxima at wavelengths of 552, 522, and 419 nm. The midpoint redox potential determined by redox titration was −0.167 V. With respect to molecular mass, redox properties, and molecular features, this cytochrome exhibited its highest similarity to the cytochromes c of Desulfovibrio salexigens and Desulfuromonas acetoxidans. The G. sulfurreducens cytochrome c reduced ferrihydrite (Fe(OH)₃), Fe(III) nitrilotriacetic acid, Fe(III) citrate, and manganese dioxide at high rates. Elemental sulfur, anthraquinone disulfonate, and humic acids were reduced more slowly. G. sulfurreducens reduced the cytochrome with acetate as an electron donor and oxidized it with fumarate. Wolinella succinogenes was able to reduce externally provided cytochrome c of G. sulfurreducens with molecular hydrogen or formate as an electron donor and oxidized it with fumarate or nitrate as an electron acceptor. A coculture could be established in which G. sulfurreducens reduced the cytochrome with acetate, and the reduced cytochrome was reoxidized by W. succinogenes in the presence of nitrate. We conclude that this cytochrome can act as iron(III) reductase for electron transfer to insoluble iron hydroxides or to sulfur, manganese dioxide, or other oxidized compounds, and it can transfer electrons to partner bacteria.     

Redox tuning of the catalytic activity of soluble fumarate reductases from Shewanella

Many enzymes involved in bioenergetic processes contain chains of redox centers that link the protein surface, where interaction with electron donors or acceptors occurs, to a secluded catalytic site. In numerous cases these redox centers can transfer only single electrons even when they are associated to catalytic sites that perform two-electron chemistry. These chains provide no obvious contribution to enhance chemiosmotic energy conservation, and often have more redox centers than those necessary to hold sufficient electrons to sustain one catalytic turnover of the enzyme. To investigate the role of such a redox chain we analyzed the transient kinetics of fumarate reduction by two flavocytochromes c₃ of Shewanella species while these enzymes were being reduced by sodium dithionite. These soluble monomeric proteins contain a chain of four hemes that interact with a flavin adenine dinucleotide (FAD) catalytic center that performs the obligatory two electron–two proton reduction of fumarate to succinate. Our results enabled us to parse the kinetic contribution of each heme towards electron uptake and conduction to the catalytic center, and to determine that the rate of fumarate reduction is modulated by the redox stage of the enzyme, which is defined by the number of reduced centers. In both enzymes the catalytically most competent redox stages are those least prevalent in a quasi-stationary condition of turnover. Furthermore, the electron distribution among the redox centers during turnover suggested how these enzymes can play a role in the switch between respiration of solid and soluble terminal electron acceptors in the anaerobic bioenergetic metabolism of Shewanella.     

Ferrihydrite reduction by Geobacter species is stimulated by secondary bacteria

Geobacter species such as G. bremensis, G. pelophilus, and G. sulfurreducens are obligately anaerobic and grow in anoxic, non-reduced medium by fast reduction of soluble ferric citrate. In contrast, insoluble ferrihydrite was either only slowly or not reduced when supplied as electron acceptor in similar growth experiments. Ferrihydrite reduction was stimulated by addition of a reducing agent or by concomitant growth of secondary bacteria that were physiologically and phylogenetically as diverse as Escherichia coli, Lactococcus lactis, or Pseudomonas stutzeri. In control experiments with heat-inactivated Geobacter cells and viable secondary bacteria, no (E. coli, P. stutzeri) or only little (L. lactis) ferrihydrite was reduced. Redox indicator dyes showed that growing E. coli, P. stutzeri, or L. lactis cells lowered the redox potential of the medium in a similar way as a reducing agent did. The lowered redox potential was presumably the key factor that stimulated ferrihydrite reduction by all three Geobacter species. The observed differences in anoxic non-reduced medium with ferric citrate versus ferrihydrite as electron acceptor indicated that reduction of these electron acceptors involved different cellular components or different biochemical strategies. Furthermore, it appears that redox-sensitive components are involved, and/or that gene expression of components needed for ferrihydrite reduction is controlled by the redox state.Dedicated to Prof. Dr. Dr. h.c. mult. Hans Günter Schlegel on the occasion of his 80th birthday.     

Limited reversibility of transmembrane proton transfer assisting transmembrane electron transfer in a dihaem-containing succinate:quinone oxidoreductase

Membrane protein complexes can support both the generation and utilisation of a transmembrane electrochemical proton potential (Δp), either by supporting transmembrane electron transfer coupled to protolytic reactions on opposite sides of the membrane or by supporting transmembrane proton transfer. The first mechanism has been unequivocally demonstrated to be operational for Δp-dependent catalysis of succinate oxidation by quinone in the case of the dihaem-containing succinate:menaquinone reductase (SQR) from the Gram-positive bacterium Bacillus licheniformis. This is physiologically relevant in that it allows the transmembrane potential Δp to drive the endergonic oxidation of succinate by menaquinone by the dihaem-containing SQR of Gram-positive bacteria. In the case of a related but different respiratory membrane protein complex, the dihaem-containing quinol:fumarate reductase (QFR) of the ?-proteobacterium Wolinella succinogenes, evidence has been obtained that both mechanisms are combined, so as to facilitate transmembrane electron transfer by proton transfer via a both novel and essential compensatory transmembrane proton transfer pathway (“E-pathway”). Although the reduction of fumarate by menaquinol is exergonic, it is obviously not exergonic enough to support the generation of a Δp. This compensatory “E-pathway” appears to be required by all dihaem-containing QFR enzymes and results in the overall reaction being electroneutral. However, here we show that the reverse reaction, the oxidation of succinate by quinone, as catalysed by W. succinogenes QFR, is not electroneutral. The implications for transmembrane proton transfer via the E-pathway are discussed.     

Succinate:quinone oxidoreductases from ϵ-proteobacteria

The ϵ-proteobacteria form a subdivision of the Proteobacteria including the genera Wolinella, Campylobacter, Helicobacter, Sulfurospirillum, Arcobacter and Dehalospirillum. The majority of these bacteria are oxidase-positive microaerophiles indicating an electron transport chain with molecular oxygen as terminal electron acceptor. However, numerous members of the ϵ-proteobacteria also grow in the absence of oxygen. The common presence of menaquinone and fumarate reduction activity suggests anaerobic fumarate respiration which was demonstrated for the rumen bacterium Wolinella succinogenes as well as for Sulfurospirillum deleyianum, Campylobacter fetus, Campylobacter rectus and Dehalospirillum multivorans. To date, complete genome sequences of Helicobacter pylori and Campylobacter jejuni are available. These bacteria and W. succinogenes contain the genes frdC, A and B encoding highly similar heterotrimeric enzyme complexes belonging to the family of succinate:quinone oxidoreductases. The crystal structure of the W. succinogenes quinol:fumarate reductase complex (FrdCAB) was solved recently, thus providing a model of succinate:quinone oxidoreductases from ϵ-proteobacteria. Succinate:quinone oxidoreductases are being discussed as possible therapeutic targets in the treatment of several pathogenic ϵ-proteobacteria.     

Isolation of the sulphur reductase and reconstitution of the sulphur respiration of Wolinella succinogenes

Wolinella succinogenes can grow at the expense of sulphur reduction by formate. The enzymes involved in the catalysis of this catabolic reaction have been investigated. From the results the following conclusions are drawn: 1. The enzyme isolated as a sulphide dehydrogenase from the cytoplasmic membrane of W. succinogenes is the functional sulphur reductase that operates in the electron transport from formate to sulphur. 2. The enzyme (M_r 200,000) consists essentially of one type of subunit with the M_r 85,000 and contains equal amounts of free iron and sulphide (120 mol/g protein), but no heme. It represents the first functional sulphur reductase ever isolated. 3. The electron transport chain catalyzing sulphur reduction by formate consists merely of formate dehydrogenase and sulphur reductase. A lipophilic quinone which mediates the transfer of electrons between enzymes in other chains, is apparently not involved. This is the first known example of a phosphorylative electron transport chain that operates without a quinone. 4. The same formate dehydrogenase appears to operate in the electron transport both with sulphur and with fumarate as the terminal electron acceptor in W. succinogenes.Abbreviations DMN 2,3-Dimethyl-1,4-naphthoquinone - DTT dithiothreitol - MK menaquinone (vitamin K₂) - PMSF phenylmethane sulfonylfluoride - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-glycine - Tea triethanolamine - Hepes 4-(2-hydroxyethyl)-1-piperazineethane sulfonate Dedicated to Professor F. Schneider (Philipps-Universität Marburg) on the occasion of his 60th birthday     

Lipid Composition of Novel Shewanella Species Isolated from Far Eastern Seas

A comparative study of the lipid composition of 26 strains (including type strains) of marine Gammaproteobacteria belonging to the genera Shewanella, Alteromonas, Pseudoalteromonas, Marinobacterium, Microbulbifer, and Marinobacter was carried out. The bacteria exhibited genus-specific profiles of ubiquinones, phospholipids, and fatty acids, which can serve as reliable chemotaxonomic markers for tentative identification of new isolates. The studied species of the genus Shewanella were distinguished by the presence of two types of isoprenoid quinones, namely, ubiquinones Q-7 and Q-8 and menaquinones MK-7 and MMK-7; five phospholipids typical of this genus, namely, phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), lyso-PE, and acyl-PG; and the fatty acids [15:0, 16:0, 16:1 (n-7), 17:1 (n-8), i-13:0, and i-15:0]. The high level of branched fatty acids (38–45%) and the presence of eicosapentaenoic acid (4%) may serve as criteria for the identification of this genus. Unlike Shewanella spp., bacteria of the other genera contained a single type of isoprenoid quinone: Q-8 (Alteromonas, Pseudoalteromonas, Marinobacterium, and Microbulbifer) or Q-9 (Marinobacter). The phospholipid compositions of these bacteria were restricted to three components: two major phospholipids (PE and PG) and a minor phospholipid, bisphosphatidic acid (Alteromonas and Pseudoalteromonas) or DPG (Marinobacterium, Microbulbifer, and Marinobacter). The bacteria exhibited genus-specific profiles of fatty acids.     

Investigation of the fumarate metabolism of the syntrophic propionate-oxidizing bacterium strain MPOB

The growth of the syntrophic propionate-oxidizing bacterium strain MPOB in pure culture by fumarate disproportionation into carbon dioxide and succinate and by fumarate reduction with propionate, formate or hydrogen as electron donor was studied. The highest growth yield, 12.2 g dry cells/mol fumarate, was observed for growth by fumarate disproportionation. In the presence of hydrogen, formate or propionate, the growth yield was more than twice as low: 4.8, 4.6, and 5.2 g dry cells/mol fumarate, respectively. The location of enzymes that are involved in the electron transport chain during fumarate reduction in strain MPOB was analyzed. Fumarate reductase, succinate dehydrogenase, and ATPase were membrane-bound, while formate dehydrogenase and hydrogenase were loosely attached to the periplasmic side of the membrane. The cells contained cytochrome c, cytochrome b, menaquinone-6 and menaquinone-7 as possible electron carriers. Fumarate reduction with hydrogen in membranes of strain MPOB was inhibited by 2-(heptyl)-4-hydroxyquinoline-N-oxide (HOQNO). This inhibition, together with the activity of fumarate reductase with reduced 2,3-dimethyl-1,4-naphtoquinone (DMNH₂) and the observation that cytochrome b of strain MPOB was oxidized by fumarate, suggested that menequinone and cytochrome b are involved in the electron transport during fumarate reduction in strain MPOB. The growth yields of fumarate reduction with hydrogen or formate as electron donor were similar to the growth yield of Wolinella succinogenes. Therefore, it can be assumed that strain MPOB gains the same amount of ATP from fumarate reduction as W. succinogenes, i.e. 0.7 mol ATP/mol fumarate. This value supports the hypothesis that syntrophic propionate-oxidizing bacteria have to invest two-thirds of an ATP via reversed electron transport in the succinate oxidation step during the oxidation of propionate. The same electron transport chain that is involved in fumarate reduction may operate in the reversed direction to drive the energetically unfavourable oxidation of succinate during syntrophic propionate oxidation since (1) cytochrome b was reduced by succinate and (2) succinate oxidation was similarly inhibited by HOQNO as fumarate reduction. Received: 18 March 1997 / Accepted: 10 November 1997     

RNA synthesis during morphogenesis of the fungusMucor racemosus

Bacteroides succinogenes produces acetate and succinate as major products of carbohydrate fermentation. An investigation of the enzymes involved indicated that pyruvate is oxidized by a flavin-dependent pyruvate cleavage enzyme to acetyl-CoA and CO₂. Active CO₂ exchange is associated with the pyruvate oxidation system. Reduction of flavin nucleotides is CoASH-dependent and does not require ferredoxin. Acetyl-CoA is further metabolized via acetyl phosphate to acetate and ATP. Reduced flavin nucleotide is used to reduce fumarate to succinate by a particulate flavin-specific fumarate reductase reaction which may involve cytochrome b. Phosphoenolpyruvate (PEP) is carboxylated to oxalacetate by a GDP-specific PEP carboxykinase. Oxalacetate, in turn, is converted to malate by a pyridine nucleotide-dependent malate dehydrogenase. The organism has a NAD-dependent glyceraldehyde-3-phosphate dehydrogenase. The data suggest that reduced pyridine nucleotides generated during glycolysis are oxidized in malate formation and that the electrons generated during pyruvate oxidation are used to reduce fumarate to succinate.     

Mercury Methylation by Dissimilatory Iron-Reducing Bacteria

The Hg-methylating ability of dissimilatory iron-reducing bacteria in the genera Geobacter, Desulfuromonas, and Shewanella was examined. All of the Geobacter and Desulfuromonas strains tested methylated mercury while reducing Fe(III), nitrate, or fumarate. In contrast, none of the Shewanella strains produced methylmercury at higher levels than abiotic controls under similar culture conditions. Geobacter and Desulfuromonas are closely related to known Hg-methylating sulfate-reducing bacteria within the Deltaproteobacteria.     

Wolinella succinogenes quinol:fumarate reductase—2.2-Å resolution crystal structure and the E-pathway hypothesis of coupled transmembrane proton and electron transfer

The structure of the respiratory membrane protein complex quinol:fumarate reductase (QFR) from Wolinella succinogenes has been determined by X-ray crystallography at 2.2-Å resolution [Nature 402 (1999) 377]. Based on the structure of the three protein subunits A, B, and C and the arrangement of the six prosthetic groups (a covalently bound FAD, three iron-sulfur clusters, and two haem b groups), a pathway of electron transfer from the quinol-oxidising dihaem cytochrome b in the membrane to the site of fumarate reduction in the hydrophilic subunit A has been proposed. The structure of the membrane-integral dihaem cytochrome b reveals that all transmembrane helical segments are tilted with respect to the membrane normal. The “four-helix” dihaem binding motif is very different from other dihaem-binding transmembrane four-helix bundles, such as the “two-helix motif” of the cytochrome bc₁ complex and the “three-helix motif” of the formate dehydrogenase/hydrogenase group. The γ-hydroxyl group of Ser C141 has an important role in stabilising a kink in transmembrane helix IV. By combining the results from site-directed mutagenesis, functional and electrochemical characterisation, and X-ray crystallography, a residue was identified which was found to be essential for menaquinol oxidation [Proc. Natl. Acad. Sci. U. S. A. 97 (2000) 13051]. The distal location of this residue in the structure indicates that the coupling of the oxidation of menaquinol to the reduction of fumarate in dihaem-containing succinate:quinone oxidoreductases could in principle be associated with the generation of a transmembrane electrochemical potential. However, it is suggested here that in W. succinogenes QFR, this electrogenic effect is counterbalanced by the transfer of two protons via a proton transfer pathway (the “E-pathway”) in concert with the transfer of two electrons via the membrane-bound haem groups. According to this “E-pathway hypothesis”, the net reaction catalysed by W. succinogenes QFR does not contribute directly to the generation of a transmembrane electrochemical potential.     

Electron transport chains and bioenergetics of respiratory nitrogen metabolism in Wolinella succinogenes and other Epsilonproteobacteria

Recent phylogenetic analyses have established that the Epsilonproteobacteria form a globally ubiquitous group of ecologically significant organisms that comprises a diverse range of free-living bacteria as well as host-associated organisms like Wolinella succinogenes and pathogenic Campylobacter and Helicobacter species. Many Epsilonproteobacteria reduce nitrate and nitrite and perform either respiratory nitrate ammonification or denitrification. The inventory of epsilonproteobacterial genomes from 21 different species was analysed with respect to key enzymes involved in respiratory nitrogen metabolism. Most ammonifying Epsilonproteobacteria employ two enzymic electron transport systems named Nap (periplasmic nitrate reductase) and Nrf (periplasmic cytochrome c nitrite reductase). The current knowledge on the architecture and function of the corresponding proton motive force-generating respiratory chains using low-potential electron donors are reviewed in this article and the role of membrane-bound quinone/quinol-reactive proteins (NapH and NrfH) that are representative of widespread bacterial electron transport modules is highlighted. Notably, all Epsilonproteobacteria lack a napC gene in their nap gene clusters. Possible roles of the Nap and Nrf systems in anabolism and nitrosative stress defence are also discussed. Free-living denitrifying Epsilonproteobacteria lack the Nrf system but encode cytochrome cd₁ nitrite reductase, at least one nitric oxide reductase and a characteristic cytochrome c nitrous oxide reductase system (cNosZ). Interestingly, cNosZ is also found in some ammonifying Epsilonproteobacteria and enables nitrous oxide respiration in W. succinogenes.     

Identification of an uptake hydrogenase required for hydrogen-dependent reduction of Fe(III) and other electron acceptors by Geobacter sulfurreducens

Geobacter sulfurreducens, a representative of the family Geobacteraceae that predominates in Fe(III)-reducing subsurface environments, can grow by coupling the oxidation of hydrogen to the reduction of a variety of electron acceptors, including Fe(III), fumarate, and quinones. An examination of the G. sulfurreducens genome revealed two operons, hya and hyb, which appeared to encode periplasmically oriented respiratory uptake hydrogenases. In order to assess the roles of these two enzymes in hydrogen-dependent growth, Hya- and Hyb-deficient mutants were generated by gene replacement. Hyb was found to be required for hydrogen-dependent reduction of Fe(III), anthraquinone-2,6-disulfonate, and fumarate by resting cell suspensions and to be essential for growth with hydrogen and these three electron acceptors. Hya, in contrast, was not. These findings suggest that Hyb is an essential respiratory hydrogenase in G. sulfurreducens.     

Growth the Wolinella succinogenes on H2S plus fumarate and on formate plus sulfur as energy sources

Wolinella succinogenes was found to grow on H₂S plus fumarate with the formation of elemental sulfur and succinate. The growth rate was 0.18 h^-1 (t _d=3.8 h) and the growth yield was estimated to be 6.0 g per mol fumarate used. Growth also occurred on formate plus elemental sulfur; the products formed were H₂S and CO₂. The growth rate and estimated growth yield were 0.58 h^-1 (t _d=1.2 h) and 3.5 g per mol formate used, respectively. These results suggest that certain chemotrophic anaerobes may be involved in both the formation and reduction of sulfur.