Description of Desulfotomaculum nigrificans subsp. salinus as a new species, Desulfotomaculum salinum sp. nov

This study focused on the physiological, chemotaxonomic, and genotypic characteristics of two thermophilic spore-forming sulfate-reducing bacterial strains, 435T and 781, of which the former has previously been assigned to the subspecies Desulfotomaculum nigrificans subsp. salinus. Both strains reduced sulfate with the resulting production of H2S on media supplemented with H2 + CO2, formate, lactate, pyruvate, malate, fumarate, succinate, methanol, ethanol, propanol, butanol, butyrate, valerate, or palmitate. Lactate oxidation resulted in acetate accumulation; butyrate was oxidized completely, with acetate as an intermediate product. Growth on acetate was slow and weak. Sulfate, sulfite, thiosulfate, and elemental sulfur, but not nitrate, served as electron acceptors for growth with lactate. The bacteria performed dismutation of thiosulfate to sulfate and hydrogen sulfide. In the absence of sulfate, pyruvate but not lactate was fermented. Cytochromes of b and c types were present. The temperature and pH optima for both strains were 60-65 degrees C and pH 7.0. Bacteria grew at 0 to 4.5-6.0% NaCl in the medium, with the optimum being at 0.5-1.0%. Phylogenetic analysis based on a comparison of incomplete 16S rRNA sequences revealed that both strains belonged to the C cluster of the genus Desulfotomaculum, exhibiting 95.5-98.3% homology with the previously described species. The level of DNA-DNA hybridization of strains 435T and 781 with each other was 97%, while that with closely related species D. kuznetsovii 17T was 51-52%. Based on the phenotypic and genotypic properties of strains 435T and 781, it is suggested that they be assigned to a new species: Desulfotomaculum salinum sp. nov., comb. nov. (type strain 435T = VKM B 1492T).     

Growth of sulfate-reducing bacteria with sulfur as electron acceptor

In addition to three new isolates, six strains of representative species of sulfate-reducing bacteria were tested for their capacity to use elemental sulfur as an electron acceptor for growth. There was good growth and sulfide production by strain Norway 4 and the three isolates, two of which had been enriched with sulfur flower and one isolated from a culture with green sulfur bacteria. Slow but definite growth was observed with Desuflovibrio gigas. The type strains of Desulfovibrio desulfuricans, D. vulgaris, and Desulfotomaculum nigrificans as well as Desulfomonas pigra did not grow with sulfur. The four strains that grew well with sulfur flower were straight, nonsporulating rods and did not contain desulfoviridin.     

Anaerobic degradation of methylmercaptan and dimethyl sulfide by newly isolated thermophilic sulfate-reducing bacteria.

The complete oxidation of methylmercaptan (MSH) and dimethyl sulfide (DMS) with sulfate or nitrate as electron acceptors was observed in enrichment cultures and dilution series using thermophilic fermentor sludge as the inoculum. Three new strains of thermophilic sulfate reducers were isolated in pure culture (strains MTS5, TDS2, and SDN4). Strain MTS5 grew on MSH and strain TDS2 grew on DMS whereas strain SDN4 grew on either MSH or DMS. The cellular growth yields were 2.57 g (dry weight)/mol of MSH for strain MTS5 and 6.02 g (dry weight)/mol of DMS for strain TDS2. All strains used sulfate, sulfite, or thiosulfate as electron acceptors, but only strain SDN4 used nitrate. DMS and MSH were oxidized to CO2 and sulfide with either sulfate or nitrate as the electron acceptor. Sulfate was stoichiometrically reduced to sulfide while nitrate was reduced to ammonium. All strains were motile rods, required biotin for growth, lacked desulfoviridin, had DNA with G+C contents of 48 to 57 mol% and probably belonged to the genus Desulfotomaculum. This is the first report of the oxidation of MSH and DMS by pure cultures of sulfate-reducing bacteria.     

Desulfovibrio capillatus sp. nov., a novel sulfate-reducing bacterium isolated from an oil field separator located in the Gulf of Mexico

A new spirilloid sulfate-reducing bacterium designated strain MET2(T) (T=type strain), was isolated from a Mexican oil field separator. Electron microscopy revealed a Gram-negative cell wall consisting of a 150nm thick undulating outer membrane. Strain MET2(T) appeared singly or in long chains and was actively motile with a corkscrew-like motion. The isolate grew optimally at 40 degrees C, pH 7.4 and 3% NaCl in a medium containing lactate, thiosulfate and yeast extract. Sulfate, sulfite, thiosulfate, and elemental sulfur served as electron acceptors but not nitrate or fumarate. Lactate, pyruvate and H(2) (with acetate as carbon source) were used as electron donors. Pyruvate was fermented. Desulfoviridin and cyt c were present. The G+C content of the DNA was 58.7mol%. Phylogenetic analysis based on 16S rDNA sequencing showed that strain MET2(T) was a member of the genus Desulfovibrio with "D. gracilis" and D. longus being its closest relatives (similarities of 98.3% and 97.1%, respectively). However, DNA-DNA hybridization studies indicated poor homologies (values <70%) with both species. On the basis of genotypic, phenotypic, and phylogenetic characteristics, strain MET2(T) (=DSM14982(T)=CIP107483(T)) is proposed as the type strain of a new species, Desulfovibrio capillatus sp. nov. GenBank accession number for the 16S rDNA sequence for MET2(T) is AY176773.     

Biochemical and Immunological Study of Cell Envelope Proteins in Sulfate-Reducing Bacteria

The envelope proteins of 5 strains of the genus Desulfotomaculum and 12 strains of the genus Desulfovibrio were studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The Desulfovibrio strains exhibited a typical gram-negative cell envelope, whereas the cell envelope of Desulfotomaculum strains appeared to be gram-positive. A close relationship between strains of Desulfotomaculum nigrificans was observed. A comparison between different species of Desulfotomaculum revealed some degree of similarity between Desulfotomaculum nigrificans and Desulfotomaculum ruminis, whereas Desulfotomaculum orientis seemed unique. The strains of Desulfovibrio salexigens were quite different from the strains of the other species of Desulfovibrio. In two of the strains of Desulfovibrio desulfuricans, a species-specific antigen was observed. The strains of Desulfovibrio vulgaris, Desulfovibrio africanus, and Desulfovibrio gigas and one strain of Desulfovibrio desulfuricans exhibited a similar outer membrane protein profile and also showed very similar antigenic reactions.     

Mycoplasma somnilux sp. nov., Mycoplasma luminosum sp. nov., and Mycoplasma lucivorax sp. nov., new sterol-requiring mollicutes from firefly beetles (Coleoptera: Lampyridae)

Strain PYAN-1T (T = type strain), which was isolated from a pupal gut of the firefly beetle Pyractonema angulata, and strains PIMN-1T and PIPN-2T, which were isolated from guts of adult Photinus marginalis and Photinus pyralis fireflies, respectively, were demonstrated to be sterol-requiring mollicutes. Cells of the three strains were shown by electron and dark-field microscopy to be small, pleomorphic, nonhelical, nonmotile bodies surrounded by single membranes. No evidence of a cell wall was observed, and the organisms were not susceptible to 500 U of penicillin per ml. The three strains grew rapidly in SP-4 broth medium. Strains PIMN-1T and PIPN-2T grew in medium supplemented with bovine serum fraction, but strain PYAN-1T did not. All three strains grew on solid media when the cultures were incubated aerobically, but only strains PYAN-1T and PIPN-2T formed colonies when anaerobic conditions were employed. The three strains catabolized glucose but hydrolyzed neither arginine nor urea. All of the strains grew at temperatures of 18 to 32 degrees C; strains PYAN-1T and PIMN-1T also grew at 10 degrees C. The optimal temperature for growth for strains PYAN-1T and PIPN-2T was 30 degrees C; strain PIMN-1T grew equally well at 30 or 32 degrees C. None of the three strains grew at 37 degrees C. The genome sizes of strains PYAN-1T, PIMN-1T, and PIPN-2T were about 527 (478 to 589), 570 (480 to 630), and 762 (635 to 871) megadaltons, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mineralization of monofluorobenzoate by a diculture under sulfate-reducing conditions

Abstract A mesophilic, dehalogenating, sulfate-reducing diculture was isolated from an anaerobic lake sediment. One strain of the diculture is proposed to be an endospore-forming Desulfotomaculum species, the second strain was a vibrioid, motile and non-sporeforming species which is tentatively assigned to the genus Desulfovibrio . The diculture was able to mineralize 4- and 2-fluorobenzoate both isomers being incompletely oxidized with the release of acetate, which was subsequently used by both sulfate-reducing strains. Other electron donors used for growth included benzoate, 3- and 4-hydroxybenzoate, protocatechuate, catechol, phenol, 2,5-dimethoxyphenol, fatty acids up to C₈, malate and pyruvate. The culture obtained from a freshwater habitat grew optimally at NaCl concentrations of 0.3–0.5 g 1⁻¹, 33–37°C, and pH 7.4. Our experiments showed that certain fluorinated aromatic hydrocarbons could serve as sole sources of carbon and energy for sulfate-reducing bacteria.     

Evaluation of the in vitro and in vivo dimorphism of Sporothrix schenckii, Blastomyces dermatitidis, and Paracoccidioides brasiliensis isolates after preservation in mineral oil

Morphological differentiation has commanded attention for its putative impact on the pathogenesis of invasive fungal infections. We evaluated in vitro and in vivo the dimorphism from mycelial to yeast-phase of Sporothrix schenckii, Blastomyces dermatitidis and Paracoccidioides brasiliensis isolates, two strains for each species, preserved in mineral oil. S. schenckii strains showed typical micromorphology at 25 degrees C but one strain was unable to complete the dimorphic process in vitro. After in vivo passage through mice the strains had the ability to turn into yeast-like cells and to form colonies on brain-heart infusion medium at 36 degrees C. B. dermatitidis strains grew as dirty white to brownish membranous colonies at 25 degrees C and their micromorphology showed thin filaments with single hyaline conidia. At 36 degrees C the colonies did not differ from those grown at 25 degrees C, but produced a transitional micromorphology. P. brasiliensis strains grew as cream-colored cerebriform colonies at 25 degrees C showing a transitional morphology. B. dermatitidis and P. brasiliensis strains did not turn into yeast-like cells in vivo. The present results demonstrate that B. dermatitidis and P. brasiliensis strains were unable to complete the dimorphic process even after in vivo passage, in contrast to the S. schenckii strain.     

Paradesulfovibrio onnuriensis gen. nov., sp. nov., a chemolithoautotrophic sulfate-reducing bacterium isolated from the Onnuri vent field of the Indian Ocean and reclassification of Desulfovibrio senegalensis as Paradesulfovibrio senegalensis comb. nov.

An anaerobic, rod-shaped, mesophilic, chemolithoautotrophic, sulfate-reducing bacterial strain IOR2T was isolated from a newly found deep-sea hydrothermal vent (OVF, Onnuri Vent Field) area in the central Indian Ocean ridge (11°24′88″ S 66°25′42″ E, 2021 m water depth). The 16S rRNA gene sequence analysis revealed that the strain IOR2T was most closely related to Desulfovibrio senegalensis BLaC1T (96.7%). However, it showed low similarity with the members of the family Desulfovibrionaceae, such as Desulfovibrio tunisiensis RB22T (94.0%), D. brasiliensis LVform1T (93.9%), D. halophilus DSM 5663T (93.7%), and Pseudodesulfovibrio aespoeensis Aspo-2T (93.2%). The strain IOR2T could grow at 23–42°C (optimum 37°C), pH 5.0–8.0 (optimum pH 7.0) and with 0.5–6.5% (optimum 3.0%) NaCl. The strain could use lactate, pyruvate, H2, and glycerol as electron donors and sulfate, thiosulfate, and sulfite as electron acceptors. The major fatty acids of the strain IOR2T were iso-C15:0, iso-C17:0, ante-iso-C15:0, and summed feature 9 (C16:0 methyl/iso-C17:1ω9c). Both the strains IOR2T and BLaC1T could grow with CO2 and H2 as the sole sources of carbon and energy, respectively. Genomic evidence for the Wood-Ljungdahl pathway in both the strains reflects chemolithoautotrophic growth. The DNA G + C content of the strain IOR2T and BLaC1T was 58.1–60.5 mol%. Based on the results of the phylogenetic and physiologic studies, Paradesulfovibrio onnuriensis gen. nov., sp. nov. with the type strain IOR2T (= KCTC 15845T = MCCC 1K04559T) was proposed to be a member of the family Desulfovibrionaceae. We have also proposed the reclassification of D. senegalensis as Paradesulfovibrio senegalensis comb. nov.     

Desulfovibrio aerotolerans sp. nov., an oxygen tolerant sulphate-reducing bacterium isolated from activated sludge

A new mesophilic sulphate-reducing bacterium, designated strain DvO5(T) (T=type strain), was isolated from the outermost sulphate reduction-positive most-probable-number tube (10(-6) dilution) of an activated sludge sample, which had been oxygenated at 100% air saturation for 120 h. The motile, Gram-negative, curved 1 by 2-5 microm and non-spore-forming cells of strain DvO5(T) existed singly or in chains. Strain DvO5(T) grew optimally at 29 degrees C, pH 6.9 and 0.05% (w/v) NaCl in a medium containing lactate, sulphate and yeast extract. Sulphite, thiosulphate and elemental sulphur also served as electron acceptors whereas nitrate, nitrite or ferric iron were not reduced. Lactate, pyruvate, H(2) (with acetate as carbon source), ethanol and glycerol efficiently supported growth as electron donors. Pyruvate and malate were fermented. Strain DvO5(T) reduced oxygen by oxidising endogenous polyglucose at rates ranging from 0.4 to 6.0 nmol O(2)/mg protein min depending on the oxygen concentration, the highest rates being observed at atmospheric oxygen saturation. The G+C content of the DNA was 57.2 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain DvO5(T) was a member of the genus Desulfovibrio with D. magneticus (98.2% 16S rRNA gene sequence similarity) and D. burkinensis (97.5% 16S rRNA gene sequence similarity) being its closest relatives among validly described species. A similar phylogenetic affiliation was obtained by sequence analyses of the genes encoding the alpha and the beta subunit of dissimilatory sulphite reductase (dsrAB) as well as the alpha subunit of adenosine-5'-phosphosulphate reductase (apsA) of strain DvO5(T). On the basis of genotypic and phenotypic characteristics, strain DvO5(T) (DSM 16695(T), JCM 12613(T)) is proposed as the type strain of a new species, Desulfovibrio aerotolerans sp. nov.     

Gamma-proteobacteria Aquicella lusitana gen. nov., sp. nov., and Aquicella siphonis sp. nov. infect protozoa and require activated charcoal for growth in laboratory media

Several isolates, belonging to two new species of the same novel genus of gamma-proteobacteria, were recovered from drilled well (borehole) and spa water at S?o Gemil in central Portugal. These organisms are phylogenetically most closely related to the strictly intracellular uncultured species of the genus Rickettsiella, which cause disease in arthropods, and to the facultatively intracellular species of the genus Legionella, some of which cause Legionnaires' disease and Pontiac fever. The S?o Gemil strains grew only on media containing charcoal, as is also true of the species of the genus LEGIONELLA: Unlike the vast majority of Legionella isolates, the new isolates did not require L-cysteine or ferric pyrophosphate for growth but like the legionellae had an absolute requirement for alpha-ketoglutarate. Strains SGT-39(T) and SGT-56 grew consistently between 30 and 43 degrees C, while strains SGT-108(T) and SGT-109 grew between 30 and 40 degrees C. The pH ranges for growth of these organisms were surprisingly narrow: strains SGT-39(T) and SGT-56 grew between pH 6.3 and 7.3, while strains SGT-108(T) and SGT-109 grew between pH 6.3 and 7.0. Both organisms proliferated in the amoeba Hartmannella vermiformis but did not grow in U937 human cells. Based on 16S rRNA gene sequence analysis and physiological, biochemical, and chemical analysis we describe two new species of one novel genus; one species is represented by strain SGT-39(T), for which we propose the name Aquicella lusitana, while strain SGT-108(T) represents a second species of the same genus, for which we propose the name Aquicella siphonis.     

Mycoplasma melaleucae sp. nov., a sterol-requiring mollicute from flowers of several tropical plants

Three sterol-requiring mollicutes from floral surfaces of two tropical plant species (Melaleuca quinquenervia and Melaleuca decora) and a single isolate from a flower of the silk oak (Grevillea robusta) were serologically indistinguishable. Strain M1T (T = type strain), isolated from Melaleuca quinquenervia, was chosen for characterization. Light and electron microscopic observations of strain M1T revealed nonhelical, nonmotile, pleomorphic coccoid cells surrounded by a single cytoplasmic membrane. No evidence of a cell wall was observed. The organism grew well in SP-4 medium, but no sustained growth occurred in conventional mycoplasma media containing horse serum. The optimum temperature for growth was 23 degrees C, but multiplication occurred over a temperature range of 10 to 30 degrees C. Growth was not observed at temperatures above 30 degrees C. Strain M1T and related strains (strains M5, M10, and SO1) catabolized glucose but hydrolyzed neither arginine nor urea. The size of the strain M1T genome was about 561 megadaltons, while the guanine-plus-cytosine content of the DNA was about 27.0 mol%. The organism was serologically unrelated to the type strains of the 80 previously recognized Mycoplasma species or to 18 other unclassified sterol-requiring strains cultivated from animal, plant, or insect sources. Recent sequencing studies of 16S rRNA demonstrated that strain M1T is a member of a clade that contains the type species of the genus Mycoplasma. Strain M1 (= ATCC 49191) is the type strain of Mycoplasma melaleucae sp. nov.     

Bacillus arsenicoselenatis, sp. nov., and Bacillus selenitireducens, sp. nov.: two haloalkaliphiles from Mono Lake, California that respire oxyanions of selenium and arsenic

Two gram-positive anaerobic bacteria (strains E1H and MLS10) were isolated from the anoxic muds of Mono Lake, California, an alkaline, hypersaline, arsenic-rich water body. Both grew by dissimilatory reduction of As(V) to As(III) with the concomitant oxidation of lactate to acetate plus CO₂. Bacillus arsenicoselenatis (strain E1H) is a spore-forming rod that also grew by dissimilatory reduction of Se(VI) to Se(IV). Bacillus selenitireducens (strain MLS10) is a short, non-spore-forming rod that grew by dissimilatory reduction of Se(IV) to Se(0). When the two isolates were cocultured, a complete reduction of Se(VI) to Se(0) was achieved. Both isolates are alkaliphiles and had optimal specific growth rates in the pH range of 8.5–10. Strain E1H had a salinity optimum at 60 g l^–1 NaCl, while strain MLS10 had optimal growth at lower salinities (24–60 g l^–1 NaCl). Both strains have limited abilities to grow with electron donors and acceptors other than those given above. Strain MLS10 demonstrated weak growth as a microaerophile and was also capable of fermentative growth on glucose, while strain E1H is a strict anaerobe. Comparative 16S rRNA gene sequence analysis placed the two isolates with other Bacillus spp. in the low G+C gram-positive group of bacteria. Received: 21 May 1998 / Accepted: 31 August 1998     

Thermodesulfobacterium hveragerdense sp. nov., and Thermodesulfovibrio islandicus sp. nov., two thermophilic sulfate reducing bacteria isolated from a Icelandic hot spring

Two thermophilic non-sporeforming sulfate-reducing bacteria (SRB) were isolated from microbial mats collected from an Icelandic hot spring. Strain JSP was a gram negative rod, with an average cell size of 2.8 x 0.5 microm. No flagella were found. Growth occurred between 55 and 74 degrees C with an optimum between 70 and 74 degrees C at pH 7.0. The G+C content was 40 mol%. Strain R1Ha3 was a gram negative vibrio-shaped rod with an average cell size of 1.7 x 0.4 microm. Motility was observed mediated by one polar flagellum. The growth optimum at pH 7.0 was 65 degrees C, and growth occurred between 45 and 70 degrees C. The G+C content was 38 mol%. In the presence of sulfate, both strains used lactate, pyruvate and H2 as electron donors. In addition, strain R1Ha3 used formate. Pyruvate was the only substrate supporting fermentative growth of both strains. Growth occurred with sulfate as well as thiosulfate as electron acceptors. Furthermore, strain R1Ha3 reduced nitrate and strain JSP reduced sulfite. Neither of the strains were able to oxidize lactate completely to CO2 and neither of the strains contained desulfoviridin. 16S rDNA sequencing placed strain JSP in the genus Thermodesulfobacterium and strain R1Ha3 in the genus Thermodesulfovibrio. Based on the DNA-DNA hybridization studies and differences in morphology and physiology to their closest relatives the two new isolates were considered as new species. Strain JSP is named Thermodesulfobacterium hveragerdense and strain R1Ha3 Thermodesulfovibrio islandicus.     

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.     

Immunomagnetically captured thermophilic sulfate-reducing bacteria from north sea oil field waters

Immunomagnetic beads (IMB) were used to recover thermophilic sulfate-reducing bacteria from oil field waters from oil production platforms in the Norwegian sector of the North Sea. IMB coated with polyclonal antibodies against whole-cell antigens of the thermophilic Thermodesulfobacterium mobile captured strains GFA1, GFA2, and GFA3. GFA1 was serologically and morphologically identical to T. mobile. GFA2 and GFA3 were spore forming and similar to the Desulfotomaculum strains T90A and T93B previously isolated from North Sea oil field waters by a classical enrichment procedure. Western blots (immunoblots) of whole cells showed that GFA2, GFA3, T90A, and T93B are different serotypes of the same Desulfotomaculum species. Monoclonal antibodies (MAb) against T. mobile type strain cells were produced and used as capture agents on IMB. These MAb, named A4F4, were immunoglobulin M; they were specific to T. mobile and directed against lipopolysaccharides. The prevailing cells immunocaptured with MAb A4F4 were morphologically and serologically similar to T. mobile type strain cells. T. mobile was not detected in these oil field waters by classical enrichment procedures. Furthermore, extraction with antibody-coated IMB allowed pure strains to be isolated directly from primary enrichment cultures without prior time-consuming subculturing and consecutive transfers to selective media.     

Properties of Desulfovibrio carbinolicus sp. nov. and Other Sulfate-Reducing Bacteria Isolated from an Anaerobic-Purification Plant

Several sulfate-reducing microorganisms were isolated from an anaerobic-purification plant. Four strains were classified as Desulfovibrio desulfuricans, Desulfovibrio sapovorans, Desulfobulbus propionicus, and Desulfovibrio sp. The D. sapovorans strain contained poly-beta-hydroxybutyrate granules and seemed to form extracellular vesicles. A fifth isolate, Desulfovibrio sp. strain EDK82, was a gram-negative, non-spore-forming, nonmotile, curved organism. It was able to oxidize several substrates, including methanol. Sulfate, sulfite, thiosulfate, and sulfur were utilized as electron acceptors. Pyruvate, fumarate, malate, and glycerol could be fermented. Because strain EDK82 could not be ascribed to any of the existing species, a new species, Desulfovibrio carbinolicus, is proposed. The doubling times of the isolates were determined on several substrates. Molecular hydrogen, lactate, propionate, and ethanol yielded the shortest doubling times (3.0 to 6.3 h). Due to the presence of support material in an anaerobic filter system, these species were able to convert sulfate to sulfide very effectively at a hydraulic retention time as short as 0.5 h.     

Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov.

A newly discovered arsenate-reducing bacterium, strain OREX-4, differed significantly from strains MIT-13 and SES-3, the previously described arsenate-reducing isolates, which grew on nitrate but not on sulfate. In contrast, strain OREX-4 did not respire nitrate but grew on lactate, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly used by sulfate reducers. Scorodite (FeAsO₄2· H₂O) an arsenate-containing mineral, provided micromolar concentrations of arsenate that supported cell growth. Physiologically and phylogenetically, strain OREX-4 was far-removed from strains MIT-13 and SES-3: strain OREX-4 grew on different electron donors and electron acceptors, and fell within the gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell together in the ɛ-subdivision of the Proteobacteria. Together, these results suggest that organisms spread among diverse bacterial phyla can use arsenate as a terminal electron acceptor, and that dissimilatory arsenate reduction might occur in the sulfidogenic zone at arsenate concentrations of environmental interest. 16S rRNA sequence analysis indicated that strain OREX-4 is a new species of the genus Desulfotomaculum, and accordingly, the name Desulfotomaculum auripigmentum is proposed. Received: 22 October 1997 / Accepted: 16 June 1997     

Diversity of substrate utilization and growth characteristics of sulfate-reducing bacteria isolated from estuarine sediment in Japan

Two different isolation methods, the dilution colony-counting method (colony-isolation) and enrichment culture, were used to isolate sulfate-reducing bacteria (SRBs) from estuarine sediment in Japan. Lactate was used as an electron donor for colony-isolation, and lactate or propionate was used for enrichment culture. All isolates were classified into six different phylogenetic groups according to the 16S rRNA gene-based analysis. The closest relatives of the colony-isolates (12 strains) were species in the genera of Desulfobacterium, Desulfofrigus, Desulfovibrio and Desulfomicrobium. The closest known relative of the lactate-enrichment isolates was Desulfovibrio acrylicus and that of the propionate-enrichment isolates was Desulfobulbus mediterraneus. All isolates were incompletely-oxidizing SRBs. Overall patterns of utilization of electron donors and acceptors, as well as fermentative substrates, differed depending on the affiliation of the strain. Furthermore, even if several strains used the same substrate, the growth rates were often significantly different depending on the strain. It was strongly suggested that various species of SRBs could coexist in the sediment by competing for common substrates as well as taking priority in favorable or specific substrates for each species and the community of SRBs should be able to oxidize almost all major intermediates of anaerobic decomposition of organic matter such as lower fatty acids, alcohols and H2 as well as amino acids. Thus, it was indicated by the phylogenetic and physiological analyses of the isolates that the SRB community composed of diverse lineages of bacteria living in anoxic estuarine sediment should be able to play an extensive role in the carbon cycle as well as the sulfur cycle of the earth.     

Growth Potential of Halophilic Bacteria Isolated from Solar Salt Environments: Carbon Sources and Salt Requirements

Eighteen strains of extremely halophilic bacteria and three strains of moderately halophilic bacteria were isolated from four different solar salt environments. Growth tests on carbohydrates, low-molecular-weight carboxylic acids, and complex medium demonstrated that the moderate halophiles and strains of the extreme halophiles Haloarcula and Halococcus grew on most of the substrates tested. Among the Halobacterium isolates were several metabolic groups: strains that grew on a broad range of substrates and strains that were essentially confined to either amino acid (peptone) or carbohydrate oxidation. One strain (WS-4) only grew well on pyruvate and acetate. Most strains of extreme halophiles grew by anaerobic fermentation and possibly by nitrate reduction. Tests of growth potential in natural saltern brines demonstrated that none of the halobacteria grew well in brines which harbor the densest populations of these bacteria in solar salterns. All grew best in brines which were unsaturated with NaCl. The high concentrations of Na⁺ and Mg²⁺ found in saltern crystallizer brines limited bacterial growth, but the concentrations of K⁺ found in these brines had little effect. MgSO₄ was relatively more inhibitory to the extreme halophiles than was MgCl₂, but the reverse was true for the moderate halophiles.