Overview of mercury methylation capacities among anaerobic bacteria including representatives of the sulphate-reducers: Implications for environmental studies

International audienceMercury methylation has been extensively reported in the literature among "Firmicutes" and "Proteobacteria." Nevertheless, results are hardly comparable because of differences in initial inorganic mercury concentrations used. The use of stable isotopic tracers now permits to study mercury transformations at concentrations close to environmental levels. Here, several strains, including strict fermentative and sulphate-reducing bacteria, were tested for their mercury methylation capacities and the results were compared with data available to date. Under such conditions, mercury methylation only occurs among the delta-Proteobacteria. The absence of relation between taxonomic/phylogenetic affiliation and mercury methylation capacities was pointed out and discussed for environmental studies

Mesotoga infera sp nov., a mesophilic member of the order Thermotogales, isolated from an underground gas storage aquifer

Strain VNs100(T), a novel mesophilic, anaerobic, rod-coccoid-shaped bacterium, having a sheath-like outer structure (toga), was isolated from a water sample collected in the area of an underground gas storage aquifer. It was non-motile with cells appearing singly (2-4 mu m long x 1-2 mu m wide), in pairs or as long chains and stained Gram-negative. Strain VNs100(T) was heterotrophic, able to use arabinose, cellobiose, fructose, galactose, glucose, lactose, lactate, mannose, maltose, raffinose, ribose, sucrose and xylose as energy sources only in the presence of elemental sulfur as terminal electron acceptor. Acetate, CO2 and sulfide were the end products of sugar metabolism. Hydrogen was not detected. Elemental sulfur, but not thiosulfate, sulfate or sulfite, were reduced to sulfide. Strain VNs100(T) grew at temperatures between 30 and 50 degrees C (optimum 45 degrees C), at pH values between 6.2 and 7.9 (optimum 7.3-7.5) and at NaCl concentrations between 0 and 15 g l(-1) (optimum 2 g l(-1)). The DNA G+C content was 47.5 mol%. The main cellular fatty acid was C-16:0. Phylogenetic analysis of the small subunit rRNA gene sequence indicated that strain VNs100(T) had as its closest relatives 'Mesotoga sulfurireducens' (97.1 % similarity) and Mesotoga prima (similarity of 97.1 % and 97.7 % with each of its two genes, respectively) within the order Thermotogales. Hybridization between strain VNS100(T) and 'M. sulfurireducens' and between strain VNS100(T) and M. prima showed 12.9 % and 20.6 % relatedness, respectively. Based on phenotypic, phylogenetic and taxonomic characteristics, strain VNs100(T) is proposed as a representative of a novel species of the genus Mesotoga in the family Thermotogaceae, order Thermotogales. The name Mesotoga infera sp. nov. is proposed. The type strain is VNs100(T) (=DSM 25546(T)=JCM 18154(T))

Mesotoga infera sp. nov., a novel mesophilic member of the order Thermotogales, isolated from an underground gas storage in France

, DOI = 10.1099Strain VNs100T, a novel mesophilic anaerobic rod-cocoid-shaped bacterium, having a sheath-like outer structure (toga) was isolated from a water sample collected in the area of underground gas storage. It was non-motile with cells Appearing singly (2-4 μm long x 1-2 μm wide), in pairs, or as long chains and stained Gram-negative. Strain VNs100T was heterotrophic, able to use arabinose, cellobiose, fructose, galactose, glucose, lactose, lactate, mannose, maltose, raffinose, ribose, sucrose and xylose as energy sources only in the presence of elemental sulfur as terminal electron acceptor. Acetate, CO2 and sulfide were the end-products of sugar metabolism. Hydrogen was not detected. Elemental sulfur, but not thiosulfate, sulfate and sulfite, were reduced into sulfide. It grew at temperatures between 30°C and 50°C (optimum 45°C), at pH between 6.2 and 7.9 (optimum 7.3-7.5) and at NaCl concentrations between 0 and 15 g.L-1 (optimum 2 g.L-1). The DNA G+C content was 47.5 mol%. The main cellular fatty acid was C16:0. Phylogenetic analysis of the small-subunit (SSU) ribosomal RNA (rRNA) gene sequence indicated that strain VNs100T had as its closest relatives 'Mesotoga sulfurireducens' (97.1 % similarity) and Mesotoga prima (similarity of 97.1 % and 97.7 % with each of its two genes respectively) within the order Thermotogales. Hybridization between strain VNS100T and 'Mesotoga sulfurireducens' and between strain VNS100T and Mesotoga prima is 12.9% and 20.6 %, respectively. Based on phenotypic, phylogenetic and taxonomic characteristics, strain VNs100T is proposed as a novel species of genus Mesotoga within the family Thermotogaceae, order Thermotogales. The name Mesotoga infera, sp. nov. is proposed. The type strain is VNs100T (= DSM 25546 = JCM 18154)

Genome Sequence of the Mercury-Methylating and Pleomorphic Desulfovibrio africanus Strain Walvis Bay▿

Desulfovibrio africanus strain Walvis Bay is an anaerobic sulfate-reducing bacterium capable of producing methylmercury (MeHg), a potent human neurotoxin. The mechanism of methylation by this and other organisms is unknown. We present the 4.2-Mb genome sequence to provide further insight into microbial mercury methylation and sulfate-reducing bacteria