Candidatus Sulfurimonas marisnigri sp. nov. and Candidatus Sulfurimonas baltica sp. nov., thiotrophic manganese oxide reducing chemolithoautotrophs of the class Campylobacteria isolated from the pelagic redoxclines of the Black Sea and the Baltic Sea.

Species of the genus Sulfurimonas are reported and isolated from terrestrial habitats and marine sediments and water columns with steep redox gradients. Here we report on the isolation of strains SoZ1 and GD2 from the pelagic redoxcline of the Black Sea and the Baltic Sea, respectively. Both strains are gram-stain-negative and appear as short and slightly curved motile rods. The autecological preferences for growth of strain SoZ1 were 0-25°C (optimum 20°C), pH 6.5-9.0 (optimum pH 7.5-8.0) and salinity 10-40gL ^-1 (optimum 25gL ^-1 ). Preferences for growth of strain GD2 were 0-20°C (optimum 15°C), pH 7.0-8.0 (optimum pH 7.0-7.5) and salinity 5-40gL ^-1 (optimum 21gL ^-1 ). Strain SoZ1 grew chemolithoautotrophically, while strain GD2 also showed heterotrophic growth with short chained fatty acids as carbon source. Both species utilized hydrogen (H ₂ ), sulfide (H ₂ S here taken as the sum of H ₂ S, HS ^- and S ^2- ), elemental sulfur (S ⁰ ) and thiosulfate (S ₂ O ₃ ^2- ) as electron donors and nitrate (NO ₃ ^- ), oxygen (O ₂ ) and particulate manganese oxide (MnO ₂ ) as electron acceptors. Based on 16S rRNA gene sequence similarity, both strains cluster within the genus Sulfurimonas with Sulfurimonas gotlandica GD1 ^T as the closest cultured relative species with a sequence similarity of 96.74% and 96.41% for strain SoZ1 and strain GD2, respectively. Strains SoZ1 and GD2 share a ribosomal 16S sequence similarity of 99.27% and were demarcated based on average nucleotide identity and average amino acid identity of the whole genome sequence. These calculations have been applied to the whole genus. We propose the names Candidatus Sulfurimonas marisnigri sp. nov. and Candidatus Sulfurimonas baltica sp. nov. for the thiotrophic manganese reducing culture isolates from the Black Sea and Baltic Sea, respectively.
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