Reductive dehalogenation of trichloroacetic acid by Trichlorobacter thiogenes gen. nov., sp. nov

A bacterium able to grow via reductive dechlorination of trichloroacetate was isolated from anaerobic soil enrichments. The isolate, designated strain K1, is a member of the delta proteobacteria and is related to other known sulfur and ferric iron reducers. In anaerobic mineral media supplemented with acetate and trichloroacetate, its doubling time was 6 h. Alternative electron donor and acceptors were acetoin and sulfur or fumarate, respectively. Trichloroacetate dehalogenation activity was constitutively present, and the dechlorination product was dichloroacetate and chloride. Trichloroacetate conversion seemed to be coupled to a novel sulfur-sulfide redox cycle, which shuttled electrons from acetate oxidation to trichloroacetate reduction. In view of its unique physiological characteristics, the name Trichlorobacter thiogenes is suggested for strain K1.     

Some studies on trichloroacetate-decomposing soil bacteria

Summary Two strains of soil bacteria were isolated in selective trichloroacetate medium. Both strains grew feebly in all media and were of doubtful systematic position although possibly related to Arthrobacter. Trichloroacetate and its theoretical dehalogenation product oxalate could serve as carbon sources, the former under release of the halogen in ionic form. Also a few other chloro-aliphatic acids could be utilized, although this was not always accompanied by a corresponding halogen release. Amino acids were stimulatory and glucose inhibitory to the dehalogenation process. One strain was most active on trichloroacetate at approx. neutral reaction and the other at pH 4–5. Neither strain was active at pH above 9. Trichloroacetate could be attacked in a reducing (thioglycollate) medium but not under wholly anaerobic conditions.     

Isolation and Characterization of Desulfovibrio dechloracetivorans sp. nov., a Marine Dechlorinating Bacterium Growing by Coupling the Oxidation of Acetate to the Reductive Dechlorination of 2-Chlorophenol

Strain SF3, a gram-negative, anaerobic, motile, short curved rod that grows by coupling the reductive dechlorination of 2-chlorophenol (2-CP) to the oxidation of acetate, was isolated from San Francisco Bay sediment. Strain SF3 grew at concentrations of NaCl ranging from 0.16 to 2.5%, but concentrations of KCl above 0.32% inhibited growth. The isolate used acetate, fumarate, lactate, propionate, pyruvate, alanine, and ethanol as electron donors for growth coupled to reductive dechlorination. Among the halogenated aromatic compounds tested, only the ortho position of chlorophenols was reductively dechlorinated, and additional chlorines at other positions blocked ortho dechlorination. Sulfate, sulfite, thiosulfate, and nitrate were also used as electron acceptors for growth. The optimal temperature for growth was 30°C, and no growth or dechlorination activity was observed at 37°C. Growth by reductive dechlorination was revealed by a growth yield of about 1 g of protein per mol of 2-CP dechlorinated, and about 2.7 g of protein per mole of 2,6-dichlorophenol dechlorinated. The physiological features and 16S ribosomal DNA sequence suggest that the organism is a novel species of the genus Desulfovibrio and which we have designated Desulfovibrio dechloracetivorans. The unusual physiological feature of this strain is that it uses acetate as an electron donor and carbon source for growth with 2-CP but not with sulfate.     

Geobacter lovleyi sp. nov. strain SZ, a novel metal-reducing and tetrachloroethene-dechlorinating bacterium

A bacterial isolate, designated strain SZ, was obtained from noncontaminated creek sediment microcosms based on its ability to derive energy from acetate oxidation coupled to tetrachloroethene (PCE)-to-cis-1,2-dichloroethene (cis-DCE) dechlorination (i.e., chlororespiration). Hydrogen and pyruvate served as alternate electron donors for strain SZ, and the range of electron acceptors included (reduced products are given in brackets) PCE and trichloroethene [cis-DCE], nitrate [ammonium], fumarate [succinate], Fe(III) [Fe(II)], malate [succinate], Mn(IV) [Mn(II)], U(VI) [U(IV)], and elemental sulfur [sulfide]. PCE and soluble Fe(III) (as ferric citrate) were reduced at rates of 56.5 and 164 nmol min(-1) mg of protein(-1), respectively, with acetate as the electron donor. Alternate electron acceptors, such as U(VI) and nitrate, did not inhibit PCE dechlorination and were consumed concomitantly. With PCE, Fe(III) (as ferric citrate), and nitrate as electron acceptors, H(2) was consumed to threshold concentrations of 0.08 +/- 0.03 nM, 0.16 +/- 0.07 nM, and 0.5 +/- 0.06 nM, respectively, and acetate was consumed to 3.0 +/- 2.1 nM, 1.2 +/- 0.5 nM, and 3.6 +/- 0.25 nM, respectively. Apparently, electron acceptor-specific acetate consumption threshold concentrations exist, suggesting that similar to the hydrogen threshold model, the measurement of acetate threshold concentrations offers an additional diagnostic tool to delineate terminal electron-accepting processes in anaerobic subsurface environments. Genetic and phenotypic analyses classify strain SZ as the type strain of the new species, Geobacter lovleyi sp. nov., with Geobacter (formerly Trichlorobacter) thiogenes as the closest relative. Furthermore, the analysis of 16S rRNA gene sequences recovered from PCE-dechlorinating consortia and chloroethene-contaminated subsurface environments suggests that Geobacter lovleyi belongs to a distinct, dechlorinating clade within the metal-reducing Geobacter group. Substrate versatility, consumption of electron donors to low threshold concentrations, and simultaneous reduction of electron acceptors suggest that strain SZ-type organisms have desirable characteristics for bioremediation applications.     

<Emphasis Type="Italic">Desulfurispirillum alkaliphilum</Emphasis> gen. nov. sp. nov., a novel obligately anaerobic sulfur- and dissimilatory nitrate-reducing bacterium from a full-scale sulfide-removing bioreactor

Strain SR 1^T was isolated under anaerobic conditions using elemental sulfur as electron acceptor and acetate as carbon and energy source from the Thiopaq bioreactor in Eerbeek (The Netherlands), which is removing H₂S from biogas by oxidation to elemental sulfur under oxygen-limiting and moderately haloalkaline conditions. The bacterium is obligately anaerobic, using elemental sulfur, nitrate and fumarate as electron acceptors. Elemental sulfur is reduced to sulfide through intermediate polysulfide, while nitrate is dissimilatory reduced to ammonium. Furthermore, in the presence of nitrate, strain SR 1^T was able to oxidize limited amounts of sulfide to elemental sulfur during anaerobic growth with acetate. The new isolate is mesophilic and belongs to moderate haloalkaliphiles, with a pH range for growth (on acetate and nitrate) from 7.5 to 10.25 (optimum 9.0), and a salt range from 0.1 to 2.5 M Na⁺ (optimum 0.4 M). According to phylogenetic analysis, SR 1^T is a member of a deep bacterial lineage, distantly related to Chrysiogenes arsenatis (Macy et al. 1996). On the basis of the phenotypic and genetic data, the novel isolate is placed into a new genus and species, Desulfurispirillum alkaliphilum (type strain SR^T = DSM 18275 = UNIQEM U250). Nucleotide sequence accession number: the GenBank/EMBL accession number of the 16S rRNA gene sequence of strain SR 1^T is DQ666683.     

Characterization of Desulfitobacterium chlororespirans sp. nov., which grows by coupling the oxidation of lactate to the reductive dechlorination of 3-chloro-4-hydroxybenzoate.

Strain Co23, an anaerobic spore-forming microorganism, was enriched and isolated from a compost soil on the basis of its ability to grow with 2,3-dichlorophenol (DCP) as its electron acceptor, ortho chlorines were removed from polysubstituted phenols but not from monohalophenols. Growth by chlororespiration was indicated by a growth yield of 3.24 g of cells per mol of reducing equivalents (as 2[H]) from lactate oxidation to acetate in the presence of 3-chloro-4-hydroxybenzoate but no growth in the absence of the halogenated electron acceptor. Other indicators of chlororespiration were the fraction of electrons from the electron donor used for dechlorination (0.67) and the H2 threshold concentration of < 1.0 ppm. Additional electron donors utilized for reductive dehalogenation were pyruvate, formate, butyrate, crotonate, and H2. Pyruvate supported homoacetogenic growth in the absence of an electron acceptor. Strain Co23 also used sulfite, thiosulfate, and sulfur as electron acceptors for growth, but it did not use sulfate, nitrate or fumarate. The temperature optimum for growth was 37 degrees C; however, the rates of dechlorination were optimum at 45 degrees C and activity persisted to temperatures as high as 55 degrees C. The 16S rRNA sequence was determined, and strain Co23 was found to be related to Desulfitobacterium dehalogenans JW/IU DC1 and Desulfitobacterium strain PCE1, with sequence similarities of 97.2 and 96.8%, respectively. The phylogenetic and physiological properties exhibited by strain Co23 place it into a new species designated Desulfitobacterium chlororespirans.     

Fermentation of maleate by a gram-negative strictly anaerobic non-spore-former,Propionivibrio dicarboxylicus gen. nov., sp. nov.

Three strains of maleate-fermenting anaerobic curved rods were isolated in pure culture from anaerobic freshwater mud samples. Among the isolates, strain CreMal1 was studied in detail. It was a mesophilic non-sporing gram-negative strict anaerobe, and grew not only on maleate but also on fumarate and l-malate, producing propionate and acetate stoichiometrically as end products. Succinate was an intermediate in the degradation of maleate. Nitrate, sulfate, and other sulfur compounds were not utilized as electron acceptors. It had 61 mol% guanine-plus-cytosine content, but possessed a single polar flagellum and did not utilize carbohydrates and lactate, unlike the genus Selenomonas. Therefore, strain CreMal1 is described as a member of Propionivibrio dicarboxylicus gen. nov., sp. nov., in the family Bacteroidaceae. Strain CreMal1 was deposited as type strain in the Japan Collection of Microorganisms and in Deutsche Sammlung von Mikroorganismen.Dedicated to Professor Dr. Norbert Pfennig on the occasion of his 65th birthday     

Isolation and characterization of two novel alkalitolerant sulfidogens from a Thiopaq bioreactor, Desulfonatronum alkalitolerans sp. nov., and Sulfurospirillum alkalitolerans sp. nov

Two obligately anaerobic sulfidogenic bacterial strains were isolated from the full-scale Thiopaq bioreactor in Lelystad (The Netherlands) removing H₂S from biogas under oxygen-limiting and moderately haloalkaline conditions. Strain HSRB-L represents a dominant culturable sulfate-reducing bacterium in the reactor. It utilizes formate, H₂ (with acetate as C-source) and lactate as e-donors, and sulfate, thiosulfate and sulfite as e-acceptors. It is haloalkalitolerant, with a pH range for lithotrophic growth from 7.5 to 9.7 (optimum at 8.5–9) and a salt range from 0.1 to 1.75 M total Na⁺ (optimum at 0.6 M). The strain is a member of the genus Desulfonatronum and is proposed as a novel species D. alkalitolerans. The second strain, strain HTRB-L1, represents a dominant thiosulfate/sulfur reducer in the reactor. It is an obligate anaerobe utilizing formate and H₂ (with acetate as C-source), lactate, pyruvate and fumarate as e-donors, and thiosulfate (incomplete reduction), sulfur, arsenate and fumarate as e-acceptors. With lactate as e-donor it also grows as an ammonifyer in the presence of nitrate and nitrite. HTRB-L1 is haloalkalitolerant, with a pH range for lithotrophic growth from 7.1 to 9.7 (optimum at 8.5) and a salt range from 0.6 to 1.5 M total Na⁺ (optimum at 0.6 M). Phylogenetic analysis showed that strain HTRB-L1 is a novel species within the genus Sulfurospirillum (Epsilonproteobacteria) for which a name Sulfurospirillum alkalitolerans is proposed.     

Selenihalanaerobacter shriftii gen. nov., sp. nov., a halophilic anaerobe from Dead Sea sediments that respires selenate

We isolated an obligately anaerobic halophilic bacterium from the Dead Sea that grew by respiration of selenate. The isolate, designated strain DSSe-1, was a gram-negative, non-motile rod. It oxidized glycerol or glucose to acetate + CO2 with concomitant reduction of selenate to selenite plus elemental selenium. Other electron acceptors that supported anaerobic growth on glycerol were nitrate and trimethylamine-N-oxide; nitrite, arsenate, fumarate, dimethylsulfoxide, thiosulfate, elemental sulfur, sulfite or sulfate could not serve as electron acceptors. Growth on glycerol in the presence of nitrate occurred over a salinity range from 100 to 240 g/l, with an optimum at 210 g/l. Analysis of the 16S rRNA gene sequence suggests that strain DSSe-1 belongs to the order Halanaerobiales, an order of halophilic anaerobes with a fermentative or homoacetogenic metabolism, in which anaerobic respiratory metabolism has never been documented. The highest 16S rRNA sequence similarity (90%) was found with Acetohalobium arabaticum (X89077). On the basis of physiological properties as well as the relatively low homology of 16S rRNA from strain DSSe-1 with known genera, classification in a new genus within the order Halanaerobiales, family Halobacteroidaceae is warranted. We propose the name Selenihalanaerobacter shriftii. Type strain is strain DSSe-1 (ATCC accession number BAA-73).     

A new 3-hydroxybutyrate fermenting anaerobe,Ilyobacter polytropus,gen. nov. sp. nov., possessing various fermentation pathways

From marine anoxic mud, a new strictly anaerobic, Gram-negative, non-sporeforming bacterium was isolated with 3-hydroxybutyrate as substrate. 3-Hydroxybutyrate and crotonate were fermented to acetate and butyrate. Glycerol was fermented to 1,3-propanediol and 3-hydroxypropionate. Acetate and formate were the only products of pyruvate or citrate fermentation. Glucose and fructose were fermented to acetate, formate and ethanol. Malate and fumarate were fermented to acetate, formate and propionate. Neither sulfate, sulfur, nor nitrate was reduced. The DNA base ratio was 32.2±0.5 mol% guanine plus cytosine. Strain CuHbu1 is described as type strain of a new genus and species, Ilyobacter polytropus gen. nov. sp. nov., in the family Bacteroidaceae.     

Propionigenium modestum gen. nov. sp. nov. a new strictly anaerobic,nonsporing bacterium growing on succinate

From marine and freshwater mud samples and from human saliva new strictly anaerobic, Gram-negative, nonsporeforming bacteria were isolated growing with succinate as sole source of carbon and energy. All strains grew in defined mineral media containing at least 1% sodium chloride. Succinate was stoichiometrically transformed to propionate und carbon dioxide; the growth yield varied between 2.1 and 2.4 g cell dry weight per mol of succinate fermented. In addition to succinate, only fumarate, l-aspartate, l-malate, oxaloacetate and pyruvate, were utilized and were stoichiometrically fermented to propionate and acetate. Yeast extract was not fermented but enhanced growth rates and yields. Neither sulfate, sulfur, nor nitrate were reduced. The DNA base ratio was 33.9±0.3 mol % guanine plus cytosine. A marine isolate, strain Gra Succ 2, is described as type strain of a new species, Propionigenium modestum gen. nov. sp. nov., in the family Bacteroidaceae.     

Pelodictyon phaeoclathratiforme sp. nov., a new brown-colored member of the Chlorobiaceae forming net-like colonies

A new strain of the green sulfur bacteria was isolated from the monimolimnion of Buchensee (near Radolfzell, Lake Constance region, FRG). Single cells were rod-shaped, nonmotile and contained gas vacuoles. Typical net-like colonies were formed by ternary fission of the cells. As photosynthetic pigments bacteriochlorophylls a, e, isorenieratene and -isorenieratene were present. Sulfide, sulfur and thiosulfate were used as electron donors during anaerobic phototrophic growth. Besides carbon dioxide, acetate and propionate could serve as carbon sources under mixotrophic conditions in the light. Like all other members of the green sulfur bacteria, the new bacterium is strictly anaerobic and obligately phototrophic. The possession of gas vacuoles and the formation of net-like colonies and the guanine plus cytosine content of the DNA (47.9 mol% G+C) are typical characteristics of the genus Pelodictyon. Because of its photosynthetic pigments which differ from those of Pelodictyon clathratiforme, strain BU 1 represents a new species, P. Phaeoclathratiforme sp. nov.     

Desulfuromonas acetoxidans gen. nov. and sp. nov., a new anaerobic,sulfur-reducing,acetate-oxidizing bacterium

Anaerobic sea or fresh water media with acetate and elemental sulfur yielded enrichments of a new type of strictly anaerobic, rod-shaped, laterally flagellated, Gram-negative bacterium. Three pure culture-strains from different sulfide-containing sea water sources were characterized in detail and are described as a new genus and species Desulfuromonas acetoxidans.The new bacterium is unable to ferment organic substances; it obtains energy for growth by anaerobic sulfur respiration. Acetate, ethanol or propanol can serve as carbon and energy source for growth; their oxidation to CO₂ is stoichiometrically linked to the reduction of elemental sulfur to sulfide. Organic disulfide compounds, malate or fumarate are the only other electron acceptors used. Butanol and pyruvate are used in the presence of malate only; no other organic compounds are utilized. Biotin is required as a growth factor. The following dry weight yields per mole of substrate are obtained: in the presence of sulfur: 4.21 g on acetate, 9.77 g on ethanol; in the presence of malate: 16.5 g on acetate, 34.2 g on ethanol and 46.2 g on pyruvate. Accumulations of cells are pink; cell suspensions exhibit absorption spectra resembling those of c-type cytochromes (abs. max. at 419, 523 and 553 nm). Malate-ethanol grown cells contain a b-type cytochrome in addition.In the presence of acetate, ethanol or propanol, Desulfuromonas strains form robust growing syntrophic mixed cultures with phototrophic green sulfur bacteria.Dedicated to Prof. Roger Y. Stanier on the occasion of his 60th barthday     

Isolation and characterization of Desulfovibrio dechloracetivorans sp. nov., a marine dechlorinating bacterium growing by coupling the oxidation of acetate to the reductive dechlorination of 2-chlorophenol

Strain SF3, a gram-negative, anaerobic, motile, short curved rod that grows by coupling the reductive dechlorination of 2-chlorophenol (2-CP) to the oxidation of acetate, was isolated from San Francisco Bay sediment. Strain SF3 grew at concentrations of NaCl ranging from 0.16 to 2.5%, but concentrations of KCl above 0. 32% inhibited growth. The isolate used acetate, fumarate, lactate, propionate, pyruvate, alanine, and ethanol as electron donors for growth coupled to reductive dechlorination. Among the halogenated aromatic compounds tested, only the ortho position of chlorophenols was reductively dechlorinated, and additional chlorines at other positions blocked ortho dechlorination. Sulfate, sulfite, thiosulfate, and nitrate were also used as electron acceptors for growth. The optimal temperature for growth was 30 degrees C, and no growth or dechlorination activity was observed at 37 degrees C. Growth by reductive dechlorination was revealed by a growth yield of about 1 g of protein per mol of 2-CP dechlorinated, and about 2.7 g of protein per mole of 2,6-dichlorophenol dechlorinated. The physiological features and 16S ribosomal DNA sequence suggest that the organism is a novel species of the genus Desulfovibrio and which we have designated Desulfovibrio dechloracetivorans. The unusual physiological feature of this strain is that it uses acetate as an electron donor and carbon source for growth with 2-CP but not with sulfate.     

Pelovirga terrestris gen. nov., sp. nov., anaerobic,alkaliphilic, fumarate-, arsenate-, Fe(III)- and sulfur-reducing bacterium isolated from a terrestrial mud volcano

A novel anaerobic, mesophilic, alkaliphilic, chemoorganotrophic bacterium (strain M08fum^T) was isolated from a salsa lake of a terrestrial mud volcano (Taman Peninsula, Russia). Cell of strain M08fum^T were Gram-stain-negative, rod-shaped, non-spore forming motile rods. The temperature range for growth was 10–45 °C (optimum at 30 °C). The pH range for growth was 7.0–11.0, with an optimum at pH 8.5–9.0. The isolate was capable of organic acids fermentation and anaerobic respiration with elemental sulfur, Fe(III) and arsenate. The end products of fumarate fermentation were succinate, acetate and CO₂. The closest phylogenetic relatives of strain M08fum^T were members of the family Geopsychrobacteraceae, class Desulfuromonadia. The genome of strain M08fum^T had a size of 3.10 Mb with a DNA G + C content of 53.1% (WGS). Genome analysis revealed the presence of genes involved in fumarate fermentation, arsenate reduction and resistance, sulfur respiration and Fe (III) reduction. Based on the phenotypic, genotypic and phylogenetic characteristics we propose to assign strain M08fum^T to a new species of a novel genus Pelovirga terrestris gen. nov., sp. nov. within the family Geopsychrobacteraceae. The type strain of Pelovirga terrestris is M08fum^T (=KCTC 15919^T = VKM B-3407^T). This is the first representative of the class Desulfuromonadia, isolated in pure culture from a mud volcano and the first alkaliphile in the family Geopsychrobacteraceae.     

Desulforhabdus amnigenus gen. nov. sp. nov., a sulfate reducer isolated from anaerobic granular sludge

From granular sludge of an upflow anaerobic sludge bed (UASB) reactor treating paper-mill wastewater, a sulfate-reducing bacterium (strain ASRB1) was isolated with acetate as sole carbon and energy source. The bacterium was rod-shaped, (1.4–1.9×2.5–3.4 μm), nonmotile, and gram-negative. Optimum growth with acetate occurred around 37°C in freshwater medium (doubling time: 3.5–5.0 days). The bacterium grew on a range of organic acids, such as acetate, propionate, and butyrate, and on alcohols, and grew autotrophically with H₂, CO₂ and sulfate. Fastest growth occurred with formate, propionate, and ethanol (doubling time: approx. 1.5 days). Strain ASRB1 clusters with the delta subdivision of Proteobacteria and is closely related toSyntrophobacter wolinii a syntrophic propionate oxidizer. Strain ASRB1 was characterized as a new genus and species:Desulforhabdus amnigenus.     

Fermentation of trihydroxybenzenes by Pelobacter acidigallici gen. nov. sp. nov., a new strictly anaerobic,non-sporeforming bacterium

Five strains of rod-shaped, Gram-negative, non-sporing, strictly anaerobic bacteria were isolated from limnic and marine mud samples with gallic acid or phloroglucinol as sole substrate. All strains grew in defined mineral media without any growth factors; marine isolates required salt concentrations higher than 1% for growth, two freshwater strains only thrived in freshwater medium. Gallic acid, pyrogallol, 2,4,6-trihydroxybenzoic acid, and phloroglucinol were the only substrates utilized and were fermented stoichiometrically to 3 mol acetate (and 1 mol CO₂) per mol with a growth yield of 10g cell dry weight per mol of substrate. Neither sulfate, sulfur, nor nitrate were reduced. The DNA base ratio was 51.8% guanine plus cytosine. A marine isolate, Ma Gal 2, is described as type strain of a new genus and species, Pelobacter acidigallici gen. nov. sp. nov., in the family Bacteroidaceae. In coculture with Acetobacterium woodii, the new isolates converted also syringic acid completely to acetate. Cocultures with Methanosarcina barkeri converted the respective substrates completely to methane and carbon dioxide.     

Natranaeroarchaeum sulfidigenes gen. nov., sp. nov., carbohydrate-utilizing sulfur-respiring haloarchaeon from hypersaline soda lakes,a member of a new family Natronoarchaeaceae fam. nov. in the order Halobacteriales

A pure culture of alkaliphilic haloarchaeon strain AArc-S^T capable of anaerobic growth by carbohydrate-dependent sulfur respiration was obtained from hypersaline lakes in southwestern Siberia. According to phylogenetic analysis, AArc-S^T formed a new genus level branch most related to the genus Natronoarchaeum in the order Halobacteriales. The strain is facultatively anaerobic with strictly respiratory metabolism growing either by anaerobic respiration with elemental sulfur and thiosulfate as the electron acceptors or by aerobic respiration at microoxic conditions. Thiosulfate is reduced partially to sulfide and sulfite. It is a first sulfur-reducing alkaliphilic haloarchaeon utilizing sugars, starch and glycerol as substrates for anaerobic growth. It is extremely halophilic (optimum at 3.5 M total Na⁺) and obligately alkaliphilic (optimum at pH 9.5). The dominant polar lipids include PG and PGP-Me with the archaeol (C₂₀-C₂₀) or extended archaeol (C₂₀-C₂₅) cores. The dominant respiratory lipoquinone is MK-8:8. On the basis of unique physiological properties and results of phylogenetic analysis, the soda lake isolate is suggested to be classified into a novel genus and species Natranaeroarchaeum sulfidigenes gen. nov., sp. nov. (=JCM 34033^T = UNIQEM U1000^T). Furthermore, on the bases of phylogenomic reconstruction, a new family Natronoarchaeaceae fam. nov. is proposed within the order Halobacteriales incorporating Natranaeroarchaeum and three related genera: Natronoarchaeum, Salinarchaeum and Halostella.     

Chemolithotrophic growth of Desulfovibrio sulfodismutans sp. nov. by disproportionation of inorganic sulfur compounds

A new Desulfovibrio strain ThAc01 was isolated from freshwater mud; the strain conserved energy for growth under strictly anaerobic conditions by disproportionation of thiosulfate or sulfite to sulfate and sulfide according to the following reactions: $$\begin{gathered} S_2 O_3^{2 - } + H_2 O \to SO_4^{2 - } + HS^ - + H^ + \hfill \\ 4SO_3^{2 - } + H^ + {\text{ }} \to 3SO_4^{2 - } + HS^ - \hfill \\ \end{gathered}$$ Strain ThAc01 required acetate as a carbon source, but was unable to utilize acetate as an oxidizable energy source. In a defined medium with acetate and bicarbonate as carbon sources, the growth yields per mol of substrate disproportionated were 2.1 g or 3.2 g dry cell mass on thiosulfate or sulfite, respectively. Strain ThAc01 was also able to grow by dissimilatory sulfate reduction with lactate, ethanol, propanol, or butanol as electron donors and carbon sources which were incompletely oxidized to the corresponding fatty acids. However, growth by sulfate reduction was slower than by disproportionation. Elemental sulfur, nitrate, fumarate, or malate did not serve as electron acceptors. Strain ThAc01 contained desulfoviridin and cytochromes; it required panthothenate and biotin as growth factors and had a DNA base ratio of 64.1 mol% G+C. Disproportionating bacteria similar to strain ThAc01 were enriched with either thiosulfate or sulfite from various freshwater, brackish or marine mud samples. Most probable number enumeration indicated that 2×10⁶ thiosulfate-disproportionating bacteria were present per ml freshwater mud. Of various other sulfate-reducing bacteria tested, only Desulfobacter curvatus (strain AcRM3) was able to disproportionate thiosulfate or sulfite. Desulfovibrio vulgaris (strain Marburg) slowly disproportionated sulfite, but effected only a slight increase in cell density. Strain ThAc01 is proposed as the type strain of a new species, Desulfovibrio sulfodismutans.