Enrichment and characterization of human-associated mucin-degrading microbial consortia by sequential passage.

Mucin is a glycoprotein secreted throughout the mammalian gastrointestinal tract that can support endogenous microorganisms in the absence of complex polysaccharides. While several mucin-degrading bacteria have been identified, the interindividual differences in microbial communities capable of metabolizing this complex polymer are not well described. To determine whether community assembly on mucin is deterministic across individuals or whether taxonomically distinct but functionally similar mucin-degrading communities are selected across fecal inocula, we used a 10-day in vitro sequential batch culture fermentation from three human donors with mucin as the sole carbon source. For each donor, 16S rRNA gene amplicon sequencing was used to characterize microbial community succession, and the short-chain fatty acid profile was determined from the final community. All three communities reached a steady-state by day 7 in which the community composition stabilized. Taxonomic comparisons amongst communities revealed that one of the final communities had Desulfovibrio, another had Akkermansia, and all three shared other members, such as Bacteroides. Metabolic output differences were most notable for one of the donor's communities, with significantly less production of acetate and propionate than the other two communities. These findings demonstrate the feasibility of developing stable mucin-degrading communities with shared and unique taxa. Furthermore, the mechanisms and efficiencies of mucin degradation across individuals are important for understanding how this community-level process impacts human health.

Desulfovibrio fairfieldensis adhesion on implantable titanium used in odontology: a preliminary study.

The study presented here aimed to assess the ability of Desulfovibrio fairfieldensis bacteria to adhere to and form biofilm on the structure of titanium used in implants. D. fairfieldensis was found in the periodontal pockets in the oral environment, indicating that these bacteria can colonize the implant-bone interface and consequently cause bone infection and implant corrosion. Plates of implantable titanium, of which surfaces were characterized by scanning electronic microscopy and Raman spectroscopy, were immersed in several suspensions of D. fairfieldensis cells containing potassium nitrate on the one hand, and artificial saliva or a sulfato-reducing bacterial culture medium on the other hand. Following various incubation timepoints bacteria were counted in different media to determine their doubling time and titanium samples are checked for and determination of the total number of adhered bacteria and biofilm formation. Adhesion of D. fairfieldensis on titanium occurs at rates ranging from 2.105 to 4.6.106 bacteria h-1cm-2 in the first 18 h of incubation on both native and implantable titanium samples. Following that time, the increase in cell numbers per h and cm2 is attributed to growth in adhered bacteria. After 30 days of incubation in a nutrient-rich medium, dense biofilms are observed forming on the implant surface where bacteria became embedded in a layer of polymers D. fairfieldensis is able of adhering to an implantable titanium surface in order to form a biofilm. Further studies are still necessary, however, to assess whether this adhesion still occurs in an environment containing saliva or serum proteins that may alter the implant surface.

Isolation and cultivation of a novel sulfate-reducing magnetotactic bacterium belonging to the genus Desulfovibrio.

Magnetotactic bacteria (MTB) synthesize magnetosomes composed of membrane-enveloped magnetite (Fe3O4) and/or greigite (Fe3S4) nanoparticles in the cells. It is known that the magnetotactic Deltaproteobacteria are ubiquitous and inhabit worldwide in the sediments of freshwater and marine environments. Mostly known MTB belonging to the Deltaproteobacteria are dissimilatory sulfate-reducing bacteria that biomineralize bullet-shaped magnetite nanoparticles, but only a few axenic cultures have been obtained so far. Here, we report the isolation, cultivation and characterization of a dissimilatory sulfate-reducing magnetotactic bacterium, which we designate "strain FSS-1". We found that the strain FSS-1 is a strict anaerobe and uses casamino acids as electron donors and sulfate as an electron acceptor to reduce sulfate to hydrogen sulfide. The strain FSS-1 produced bullet-shaped magnetite nanoparticles in the cells and responded to external magnetic fields. On the basis of 16S rRNA gene sequence analysis, the strain FSS-1 is a member of the genus Desulfovibrio, showing a 96.7% sequence similarity to Desulfovibrio putealis strain B7-43T. Futhermore, the magnetosome gene cluster of strain FSS-1 was different from that of Desulfovibrio magneticus strain RS-1. Thus, the strain FSS-1 is considered to be a novel sulfate-reducing magnetotactic bacterium belonging to the genus Desulfovibrio.

Desulfovibrio subterraneus sp. nov., a mesophilic sulfate-reducing deltaproteobacterium isolated from a deep siliceous mudstone formation.

A novel mesophilic sulfate-reducing bacterium, strain HN2T, was isolated from groundwater sampled from the subsurface siliceous mudstone of the Wakkanai Formation located in Horonobe, Hokkaido, Japan. The bacterium was Gram-negative and vibrio-shaped, and its motility was conferred by a single polar flagellum. Cells had desulfoviridin. Catalase and oxidase activities were not detected. It grew in the temperature range of 25-40 °C (optimum, 35 °C) and pH range of 6.3-8.1 (optimum, pH 7.2-7.6). It used sulfate, thiosulfate, dimethyl sulfoxide, anthraquinone-2,6-disulfonate, Fe3+, and manganese oxide, but not elemental sulfur, nitrite, nitrate, or fumarate as electron acceptors. The strain showed weak growth with sulfite as the electron acceptor. Fermentative growth with pyruvate, lactate and cysteine was observed in the absence of sulfate, but not with malate or fumarate. NaCl was not required, but the strain tolerated up to 40 g l-1. Strain HN2T did not require vitamins. The major cellular fatty acids were iso-C15 : 0 (23.8 %), C18 : 1 ω9t (18.4 %), C18 : 0 (15.0 %), C16 : 0 (14.5 %), and anteiso-C17 :0 (10.1 %). The major respiratory quinone was menaquinone MK-6(H2). The G+C content of the genomic DNA was 56.7 mol%. Based on 16S rRNA gene sequence analysis, the closest phylogenetic relative of strain HN2T is Desulfovibrio psychrotolerans JS1T (97.0 %). Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values of the strains HN2T and D. psychrotolerans JS1T were 22.2 and 79.8 %, respectively. Based on the phenotypic and molecular genetic evidence, we propose a novel species, D. subterraneus sp. nov. with the type strain HN2T (=DSM 101010T=NBRC 112213T).

Cupidesulfovibrio liaohensis gen. nov., sp. nov., a novel sulphate-reducing bacterium isolated from an oil reservoir and reclassification of Desulfovibrio oxamicus and Desulfovibrio termitidis as Cupidesulfovibrio oxamicus comb. nov. and Cupidesulfovibrio termitidis comb. nov.

A novel sulphate-reducing, Gram-stain-negative, anaerobic strain, isolate XJ01T, recovered from production fluid at the LiaoHe oilfield, PR China, was the subject of a polyphasic study. The isolate together with Desulfovibrio oxamicus NCIMB 9442T and Desulfovibrio termitidis DSM 5308T formed a distinct, well-supported clade in the Desulfovibrionaceae 16S rRNA gene tree. The taxonomic status of the clade was underscored by complementary phenotypic data. The three isolates comprising the clade formed distinct phyletic branches and were distinguished using a combination of physiological features and by low average nucleotide identity and digital DNA-DNA hybridization values. Consequently, it is proposed that isolate XJ01T represents a novel genus and species for which the name Cupidesulfovibrio liaohensis gen. nov., sp. nov. is proposed with the type strain XJ01T (=CGMCC 1.5227T=DSM 107637T). It is also proposed that D. oxamicus and D. termitidis be reclassified as Cupidesulfovibrio oxamicus comb. nov. and Cupidesulfovibrio termitidis comb. nov., respectively.

Desulfolutivibrio sulfoxidireducens gen. nov., sp. nov., isolated from a pyrite-forming enrichment culture and reclassification of Desulfovibrio sulfodismutans as Desulfolutivibrio sulfodismutans comb. nov.

Two strains of sulfate-reducing bacteria (J.5.4.2-L4.2.8T and J.3.6.1-H7) were isolated from a pyrite-forming enrichment culture and were compared phylogenetically and physiologically to the closest related type strain Desulfovibrio sulfodismutans DSM 3696T. The isolated strains were vibrio-shaped, motile rods that stained Gram-negative. Growth occurred from 15 to 37°C and within a pH range of 6.5-8.5. Both strains used sulfate, thiosulfate, sulfite, and dimethyl sulfoxide (DMSO) as electron acceptor when grown with lactate. Lactate was incompletely oxidized to acetate. Formate and H2 were used as electron donor in the presence of acetate. Dismutation of thiosulfate and pyrosulfite was observed. The two new isolates differed from D. sulfodismutans by the utilization of DMSO as electron acceptor, 82% genome-wide average nucleotide identity (ANI) and 32% digital DNA-DNA hybridization (dDDH), thus representing a novel species. The type strain of the type species Desulfovibrio desulfuricans Essex6T revealed merely 88% 16S rRNA gene identity and 49% genome-wide average amino acid identity (AAI) to the new isolates as well as to D. sulfodismutans. Furthermore, the dominance of menaquinone MK-7 over MK-6 and the dominance of ai-C15:0 fatty acids were observed not only in the two new isolated strains but also in D. sulfodismutans. Therefore, the definition of a new genus is indicated for which the name Desulfolutivibrio is proposed. We propose for strains J.5.4.2-L4.2.8T and J.3.6.1-H7 the name Desulfolutivibrio sulfoxidireducens gen. nov. sp. nov. with strain J.5.4.2-L4.2.8T defined as type strain. In addition, we propose the reclassification of Desulfovibrio sulfodismutans as Desulfolutivibrio sulfodismutans comb. nov.

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.

Genome insights of mercury methylation among Desulfovibrio and Pseudodesulfovibrio strains.

Mercury methylation converts inorganic mercury into the toxic methylmercury, and the consequences of this transformation are worrisome for human health and the environment. This process is performed by anaerobic microorganisms, such as several strains related to Pseudodesulfovibrio and Desulfovibrio genera. In order to provide new insights into the molecular mechanisms of mercury methylation, we performed a comparative genomic analysis on mercury methylators and non-methylators from (Pseudo)Desulfovibrio strains. Our results showed that (Pseudo)Desulfovibrio species are phylogenetically and metabolically distant and consequently, these genera should be divided into various genera. Strains able to perform methylation are affiliated with one branch of the phylogenetic tree, but, except for hgcA and hgcB genes, no other specific genetic markers were found among methylating strains. hgcA and hgcB genes can be found adjacent or separated, but proximity between those genes does not promote higher mercury methylation. In addition, close examination of the non-methylator Pseudodesulfovibrio piezophilus C1TLV30 strain, showed a syntenic structure that suggests a recombination event and may have led to hgcB depletion. The genomic analyses identify also arsR gene coding for a putative regulator upstream hgcA. Both genes are cotranscribed suggesting a role of ArsR in hgcA expression and probably a role in mercury methylation.

Dose Effects of Orally Administered Spirulina Suspension on Colonic Microbiota in Healthy Mice.

Oral supplemented nutraceuticals derived from food sources are surmised to improve the human health through interaction with the gastrointestinal bacteria. However, the lack of fundamental quality control and authoritative consensus (e.g., formulation, route of administration, dose, and dosage regimen) of these non-medical yet bioactive compounds are one of the main practical issues resulting in inconsistent individual responsiveness and confounded clinical outcomes of consuming nutraceuticals. Herein, we studied the dose effects of widely used food supplement, microalgae spirulina (Arthrospira platensis), on the colonic microbiota and physiological responses in healthy male Balb/c mice. Based on the analysis of 16s rDNA sequencing, compared to the saline-treated group, oral administration of spirulina once daily for 24 consecutive days altered the diversity, structure, and composition of colonic microbial community at the genus level. More importantly, the abundance of microbial taxa was markedly differentiated at the low (1.5 g/kg) and high (3.0 g/kg) dose of spirulina, among which the relative abundance of Clostridium XIVa, Desulfovibrio, Eubacterium, Barnesiella, Bacteroides, and Flavonifractor were modulated at various degrees. Evaluation of serum biomarkers in mice at the end of spirulina intervention showed reduced the oxidative stress and the blood lipid levels and increased the level of appetite controlling hormone leptin in a dose-response manner, which exhibited the significant correlation with differentially abundant microbiota taxa in the cecum. These findings provide direct evidences of dose-related modulation of gut microbiota and physiological states by spirulina, engendering its future mechanistic investigation of spirulina as potential sources of prebiotics for beneficial health effects via the interaction with gut microbiota.

Isolation of Desulfovibrio spp. from human gut microbiota using a next-generation sequencing directed culture method.

Desulfovibrio spp. is predominant member of sulphate-reducing bacteria in human gut microbiota. Previous studies indicated that the isolation of Desulfovibrio strains from human faecal samples is very important to study the roles of human intestinal Desulfovibrio spp. in maintaining healthy states or causing diseases, as well as defining their biological characteristics. However, there are very few reports describing the isolation of Desulfovibrio spp. from human faecal samples. In this study, faecal samples were inoculated into various media containing different components. The enriched culture communities were identified using 16S rRNA gene high-throughput sequencing analysis, enabling us to identify the specific components that enable the enrichment of Desulfovibrio. Using this information, we developed five specific media and identified an effective enrichment medium that produced the highest relative abundance of Desulfovibrio in communities cultured from four faecal samples (26·5, 73·5, 44·7 and 77·6% respectively). In addition, the major non-Desulfovibrio genera were identified. Finally, three species of Desulfovibrio, D. desulfuricans, D. piger and D. legallii were isolated, representing the first time that has D. legallii been isolated from a human gastrointestinal source. SIGNIFICANCE AND IMPACT OF THE STUDY: ost of the human intestinal bacteria have not been cultured because of lack of appropriate culture method and appropriate media. Desulfovibrio spp. is associated with several clinical conditions like inflammatory bowel disease, but until now there are very few reports describing the isolation of Desulfovibrio spp. from human faecal samples. In this study, 16S rRNA gene high-throughput sequencing analysis was applied to screen appropriate enrichment media and selective cultivation of Desulfovibrio. This sequencing-based directed culture method described here can be used for the selective cultivation of gut bacteria of interest.

Desulfovibrio gilichinskyi sp. nov., a cold-adapted sulfate-reducing bacterium from a Yamal Peninsula cryopeg.

A psychrotolerant non-spore-forming sulfate-reducing bacterium, strain K3ST, was isolated from a Yamal Peninsula cryopeg within permafrost. Strain K3ST grew at subzero temperatures and required Na+ for growth. The new bacterium was able to use lactate, formate, pyruvate, fumarate, alanine, ethanol and molecular hydrogen as electron donors in the presence of sulfate, and used sulfate, sulfite, thiosulfate and elemental sulfur as electron acceptors in the presence of lactate. Fe(III)-citrate and Fe(III)-EDTA were reduced without visible growth. Major polar lipids were рhosphatidylserine, рhosphatidylethanolamine, phospholipids, cardiolipin and aminolipid; major cellular fatty acids were C16 : 1ω7, C16 : 0 and C18 : 1ω7; and the predominant isoprenoid quinone was MK-6 (H2). The genomic DNA G+C content was found to be 42.33 mol%. Phylogenetic analysis showed that the closest relative of the new isolate was Desulfovibrio ferrireducens strain 61T with 97.1 % 16S rRNA gene similarity. In addition, the ANI value between strain K3ST and D. ferrireducens 61T was 82.1 %. On the basis of the genomic and polyphasic taxonomy data of strain K3ST, we conclude that the strain is a representative of a novel species Desulfovibrio gilichinskyi sp. nov. (=VKM B-2877T=DSM 100341T).

Change in the microbial community of saline geothermal fluids amended with a scaling inhibitor: effects of heat extraction and nitrate dosage.

Geothermal plants are often affected by corrosion caused by microbial metabolites such as H2S. In the Bad Blumau (Austria) geothermal system, an increase in microbially produced H2S was observed in the hot (107 °C) and scaling inhibitor-amended saline fluids and in fluids that had cooled down (45 °C). Genetic fingerprinting and quantification revealed the dominance, increasing abundance and diversity of sulfate reducers such as Desulfotomaculum spp. that accompanied the cooling and processing of the geothermal fluids. In addition, a δ34S isotopic signature showed the microbial origin of the H2S that has been produced either chemolithotrophically or chemoorganotrophically. A nitrate addition test in a test pipe as a countermeasure against the microbial H2S formation caused a shift from a biocenosis dominated by bacteria of the phylum Firmicutes to a community of Firmicutes and Proteobacteria. Nitrate supported the growth of nitrate-reducing sulfur-oxidizing Thiobacillus thioparus, which incompletely reduced nitrate to nitrite. The addition of nitrate led to a change in the composition of the sulfate-reducing community. As a result, representatives of nitrate- and nitrite-reducing SRB, such as Desulfovibrio and Desulfonatronum, emerged as additional community members. The interaction of sulfate-reducing bacteria and nitrate-reducing sulfur-oxidizing bacteria (NR-SOB) led to the removal of H2S, but increased the corrosion rate in the test pipe.

Toxicity of hydrogen sulfide toward sulfate-reducing bacteria Desulfovibrio piger Vib-7.

Sulfate-reducing bacteria (SRB) belonging to the intestinal microbiota are the main producers of hydrogen sulfide and their increasing amount due to the accumulation of this compound in the bowel are involved in the initiation and maintenance of inflammatory bowel disease. The purpose of this experiment is to study the relative toxicity of hydrogen sulfide and survival of Desulfovibrio piger Vib-7 through monitoring: sulfate reduction parameters (sulfate consumption, hydrogen sulfide production, lactate consumption and acetate production) and kinetic parameters of these processes. The research is highlighting the survival of intestinal SRB, D. piger Vib-7 under the influence of different hydrogen sulfide concentrations (1-7 mM). The highest toxicity of H2S was measured in the presence of concentrations higher than 6 mM, where growing was stopped, though metabolic activities were not 100% inhibited. These findings are confirmed by cross correlation and principal component analysis that clearly supported the above mentioned results. The kinetic parameters of bacterial growth and sulfate reduction were inhibited proportionally with increasing H2S concentration. The presence of 5 mM H2S resulted in two times longer lag phase and generation time was eight times longer. Maximum rate of growth and hydrogen production was stopped under 4 mM, emphasizing the H2S toxicity concentrations to be < 4 mM, even for sulfide producing bacteria such as Desulfovibrio. The results are confirming H2S concentrations toxicity toward Desulfovibrio, especially the study novelty should be emphasized where it was found that the exact H2S limits (> 4 mM) toward this bacterial strain inhabiting humans and animals intestine.

The bacterial MrpORP is a novel Mrp/NBP35 protein involved in iron-sulfur biogenesis.

Despite recent advances in understanding the biogenesis of iron-sulfur (Fe-S) proteins, most studies focused on aerobic bacteria as model organisms. Accordingly, multiple players have been proposed to participate in the Fe-S delivery step to apo-target proteins, but critical gaps exist in the knowledge of Fe-S proteins biogenesis in anaerobic organisms. Mrp/NBP35 ATP-binding proteins are a subclass of the soluble P-loop containing nucleoside triphosphate hydrolase superfamily (P-loop NTPase) known to bind and transfer Fe-S clusters in vitro. Here, we report investigations of a novel atypical two-domain Mrp/NBP35 ATP-binding protein named MrpORP associating a P-loop NTPase domain with a dinitrogenase iron-molybdenum cofactor biosynthesis domain (Di-Nase). Characterization of full length MrpORP, as well as of its two domains, showed that both domains bind Fe-S clusters. We provide in vitro evidence that the P-loop NTPase domain of the MrpORP can efficiently transfer its Fe-S cluster to apo-target proteins of the ORange Protein (ORP) complex, suggesting that this novel protein is involved in the maturation of these Fe-S proteins. Last, we showed for the first time, by fluorescence microscopy imaging a polar localization of a Mrp/NBP35 protein.

The bacterial community significantly promotes cast iron corrosion in reclaimed wastewater distribution systems.

BACKGROUND: Currently, the effect of the bacterial community on cast iron corrosion process does not reach consensus. Moreover, some studies have produced contrasting results, suggesting that bacteria can either accelerate or inhibit corrosion. RESULTS: The long-term effects of the bacterial community on cast iron corrosion in reclaimed wastewater distribution systems were investigated from both spatial (yellow layer vs. black layer) and temporal (1-year dynamic process) dimensions of the iron coupon-reclaimed wastewater microcosm using high-throughput sequencing and flow cytometry approaches. Cast iron coupons in the NONdisinfection and UVdisinfection reactors suffered more severe corrosion than did those in the NaClOdisinfection reactor. The bacterial community significantly promoted cast iron corrosion, which was quantified for the first time in the practical reclaimed wastewater and found to account for at least 30.5% ± 9.7% of the total weight loss. The partition of yellow and black layers of cast iron corrosion provided more accurate information on morphology and crystal structures for corrosion scales. The black layer was dense, and the particles looked fusiform, while the yellow layer was loose, and the particles were ellipse or spherical. Goethite was the predominant crystalline phase in black layers, while corrosion products mainly existed as an amorphous phase in yellow layers. The bacterial community compositions of black layers were distinctly separated from yellow layers regardless of disinfection methods. The NONdisinfection and UVdisinfection reactors had a more similar microbial composition and variation tendency for the same layer type than did the NaClOdisinfection reactor. Biofilm development can be divided into the initial start-up stage, mid-term development stage, and terminal stable stage. In total, 12 potential functional genera were selected to establish a cycle model for Fe, N, and S metabolism. Desulfovibrio was considered to accelerate the transfer of Fe0 to Fe2+ and speed up weight loss. CONCLUSION: The long-term effect of disinfection processes on corrosion behaviors of cast iron in reclaimed wastewater distribution systems and the hidden mechanisms were deciphered for the first time. This study established a cycle model for Fe, N, and S metabolism that involved 12 functional genera and discovered the significant contribution of Desulfovibrio in promoting corrosion.

Characterization of Desulfovibrio salinus sp. nov., a slightly halophilic sulfate-reducing bacterium isolated from a saline lake in Tunisia.

A novel slightly halophilic sulfate-reducing bacterium, designated strain P1BSRT, was isolated from water of a saline lake in Tunisia. Strain P1BSRT had motile (single polar flagellum), Gram-negative, rod-shaped, non-spore-forming cells, occurring singly or in pairs. Strain P1BSRT grew at temperatures between 15 and 45 °C (optimum 40 °C), and in a pH range between 6 and 8.5 (optimum pH 6.7). The strain required NaCl for growth (1 % w/v), and tolerated high NaCl concentration (up to 12 % w/v) with an optimum of 3 % (w/v). Sulfate, thiosulfate and sulfite served as terminal electron acceptors, but not elemental sulfur, fumarate, nitrate and nitrite. Strain P1BSRT utilized lactate, pyruvate, formate, d-fructose and glycerol as carbon and energy sources. The main cellular fatty acid was C16 : 0 (50.8 %). The genomic DNA G+C content was 47.7 mol%. Phylogenetic analysis of 16S rRNA gene sequence similarity indicated that strain P1BSRT was affiliated to the genus Desulfovibrio, with the type strains Desulfovibrio salexigens (96.51 %), Desulfovibrio zosterae (95.68 %), Desulfovibrio hydrothermalis (94.81 %) and Desulfovibrio ferrireducens (94.73 %) as its closest phylogenetic relatives. On the basis of genotypic, phenotypic and phylogenetic characteristics, it is proposed to assign strain P1BSRT to a novel species of the genus Desulfovibrio, Desulfovibrio salinus sp. nov. The type strain is P1BSRT (=DSM 101510T=JCM 31065T).

Biosensor for screening bacterial mercury methylation: example within the Desulfobulbaceae.

Mercury methylation and demethylation processes govern the fate of methylmercury in aquatic ecosystems. Under anoxic conditions, methylation activity is mainly of biological origin and is often the result of sulfate-reducing bacteria. In this study, the use of a luminescent biosensor for screening methylmercury production was validated by exposing the reporter strain to methylating or non-methylating Desulfovibrio strains. The sensitivity of the biosensor to methylmercury was shown to depend on sulfate-reducing bacterial growth conditions. Bioluminescence was measured using 1-10 mM of sulfides. As the sulfide level increased, luminescence decreased by 40-70%, respectively. Nevertheless, assuming an average of 5 mM of sulfide produced during sulfate-reducing growth, a mercury methylation potential of over 4% was detected when using 185 nM of inorganic mercury. Due to technical limitations, mercury speciation has, to date, only been investigated in a small number of bacterial strains, and no consistent phylogenetic distribution has been identified. Here, the biosensor was further used to assess the Hg methylation capacities of an additional 21 strains related to the Desulfobulbaceae. Seven of them were identified as methylmercury producers. Cultivation procedures combined with bacterial biosensors could provide innovative tools to identify new methylator clades amongst the prokaryotes.

Desulfovibrio senegalensis sp. nov., a mesophilic sulfate reducer isolated from marine sediment.

Several strains of sulfate-reducing bacteria were isolated from marine sediments recovered from Hann Bay (Senegal). All were related to members of the genus Desulfovibrio. A strictly anaerobic, mesophilic and moderately halophilic strain designated BLaC1T was further characterized. Cells of strain BLaC1T stained Gram-negative and were 0.5 µm wide and 2-4 µm long, motile, rod-shaped and non-spore-forming. The four major fatty acids were anteiso-C15 : 0, iso-C15 : 0, iso-C17 : 0 and anteiso-C17 : 0. Growth was observed from 15 to 45 °C (optimum 40 °C) and at pH 5.5-8 (optimum pH 7.5). The salinity range for growth was 5-65 g NaCl l-1 (optimum 30 g l-1). Yeast extract was required for growth. Strain BLaC1T was able to grow on lactate and acetate in the presence of sulfate as an electron acceptor. Sulfate, thiosulfate and sulfite could serve as terminal electron acceptors, but not fumarate, nitrate or elemental sulfur. The DNA G+C content was 55.8 mol%. 16S rRNA gene sequence analysis assigned strain BLaC1T to the family Desulfovibrionaceae; its closest relative was Desulfovibrio oxyclinae DSM 19275T (93.7 % similarity). On the basis of 16S rRNA gene sequence comparisons and physiological characteristics, strain BLaC1T is proposed as representing a novel species of Desulfovibrio, with the name Desulfovibrio senegalensis sp. nov. The type strain is BLaC1T (=DSM 101509T=JCM 31063T).

Selection for novel, acid-tolerant Desulfovibrio spp. from a closed Transbaikal mine site in a temporal pH-gradient bioreactor.

Almost all the known isolates of acidophilic or acid-tolerant sulphate-reducing bacteria (SRB) belong to the spore-forming genus Desulfosporosinus in the Firmicutes. The objective of this study was to isolate acidophilic/acid-tolerant members of the genus Desulfovibrio belonging to deltaproteobacterial SRB. The sample material originated from microbial mat biomass submerged in mine water and was enriched for sulphate reducers by cultivation in anaerobic medium with lactate as an electron donor. A stirred tank bioreactor with the same medium composition was inoculated with the sulphidogenic enrichment. The bioreactor was operated with a temporal pH gradient, changing daily, from an initial pH of 7.3 to a final pH of 3.7. Among the bacteria in the bioreactor culture, Desulfovibrio was the only SRB group retrieved from the bioreactor consortium as observed by 16S rRNA-targeted denaturing gradient gel electrophoresis. Moderately acidophilic/acid-tolerant isolates belonged to Desulfovibrio aerotolerans-Desulfovibrio carbinophilus-Desulfovibrio magneticus and Desulfovibrio idahonensis-Desulfovibrio mexicanus clades within the genus Desulfovibrio. A moderately acidophilic strain, Desulfovibrio sp. VK (pH optimum 5.7) and acid-tolerant Desulfovibrio sp. ED (pH optimum 6.6) dominated in the bioreactor consortium at different time points and were isolated in pure culture.

Microbial potential for carbon and nutrient cycling in a geogenic supercritical carbon dioxide reservoir.

Microorganisms catalyze carbon cycling and biogeochemical reactions in the deep subsurface and thus may be expected to influence the fate of injected supercritical (sc) CO2 following geological carbon sequestration (GCS). We hypothesized that natural subsurface scCO2 reservoirs, which serve as analogs for the long-term fate of sequestered scCO2 , harbor a 'deep carbonated biosphere' with carbon cycling potential. We sampled subsurface fluids from scCO2 -water separators at a natural scCO2 reservoir at McElmo Dome, Colorado for analysis of 16S rRNA gene diversity and metagenome content. Sequence annotations indicated dominance of Sulfurospirillum, Rhizobium, Desulfovibrio and four members of the Clostridiales family. Genomes extracted from metagenomes using homology and compositional approaches revealed diverse mechanisms for growth and nutrient cycling, including pathways for CO2 and N2 fixation, anaerobic respiration, sulfur oxidation, fermentation and potential for metabolic syntrophy. Differences in biogeochemical potential between two production well communities were consistent with differences in fluid chemical profiles, suggesting a potential link between microbial activity and geochemistry. The existence of a microbial ecosystem associated with the McElmo Dome scCO2 reservoir indicates that potential impacts of the deep biosphere on CO2 fate and transport should be taken into consideration as a component of GCS planning and modelling.