Water Masses and Depth Structure Prokaryotic and T4-Like Viral Communities Around Hydrothermal Systems of the Nordic Seas.

The oceanographic features of the Nordic Seas, situated between Iceland and Svalbard, have been extensively studied over the last decades. As well, the Nordic Seas hydrothermal systems situated on the Arctic Mid-Ocean Ridge System have received an increasing interest. However, there is very little knowledge on the microbial communities inhabiting the water column of the Nordic Seas, and nothing is known about the influence of the different water masses and hydrothermal plumes on the microbial community structures. In this study, we aimed at characterizing the impact of hydrothermal plumes on prokaryotic and T4-like viral communities around the island of Jan Mayen. To this end, we used 16S rRNA-gene and g23-gene profiling as well as flow cytometry counts to examine prokaryotic and viral communities in 27 samples obtained from different water masses in this area. While Thaumarchaeota and Marine group II Archaea dominated the waters deeper than 500 m, members of Flavobacteria generally dominated the shallower waters. Furthermore, extensive chemical and physical characteristics of all samples were obtained, including temperature measurements and concentrations of major ions and gases. The effect of these physiochemical variables on the communities was measured by using constrained and unconstrained multivariate analyzes, Mantel tests, network analyzes, phylogenetic analyzes, taxonomic analyzes and temperature-salinity (Θ-S) plots. Our results suggest that hydrothermal activity has little effect on pelagic microbial communities in hydrothermal plumes of the Nordic Seas. However, we provide evidences that observed differences in prokaryotic community structure can largely be attributed to which water mass each sample was taken from. In contrast, depth was the major factor structuring the T4-like viral communities. Our results also show that it is crucial to include water masses when studying the influence of hydrothermal plumes on microbial communities, as it could prevent to falsely associate a change in community structure with the presence of a plume.

Physiological and genomic characterization of Arcobacter anaerophilus IR-1 reveals new metabolic features in Epsilonproteobacteria.

In this study we characterized and sequenced the genome of Arcobacter anaerophilus strain IR-1 isolated from enrichment cultures used in nitrate-amended corrosion experiments. A. anaerophilus IR-1 could grow lithoautotrophically on hydrogen and hydrogen sulfide and lithoheterothrophically on thiosulfate and elemental sulfur. In addition, the strain grew organoheterotrophically on yeast extract, peptone, and various organic acids. We show for the first time that Arcobacter could grow on the complex organic substrate tryptone and oxidize acetate with elemental sulfur as electron acceptor. Electron acceptors utilized by most Epsilonproteobacteria, such as oxygen, nitrate, and sulfur, were also used by A. anaerophilus IR-1. Strain IR-1 was also uniquely able to use iron citrate as electron acceptor. Comparative genomics of the Arcobacter strains A. butzleri RM4018, A. nitrofigilis CI and A. anaerophilus IR-1 revealed that the free-living strains had a wider metabolic range and more genes in common compared to the pathogen strain. The presence of genes for NAD(+)-reducing hydrogenase (hox) and dissimilatory iron reduction (fre) were unique for A. anaerophilus IR-1 among Epsilonproteobacteria. Finally, the new strain had an incomplete denitrification pathway where the end product was nitrite, which is different from other Arcobacter strains where the end product is ammonia. Altogether, our study shows that traditional characterization in combination with a modern genomics approach can expand our knowledge on free-living Arcobacter, and that this complementary approach could also provide invaluable knowledge about the physiology and metabolic pathways in other Epsilonproteobacteria from various environments.

Rhabdothermus arcticus gen. nov., sp. nov., a member of the family Thermaceae isolated from a hydrothermal vent chimney in the Soria Moria vent field on the Arctic Mid-Ocean Ridge.

A novel thermophilic member of the family Thermaceae, designated strain 2M70-1(T), was isolated from the wall of an active white smoker chimney collected in the Soria Moria vent field at 71 °N in the Norwegian-Greenland Sea. Cells of the strain were Gram-negative, non-motile rods. Growth was observed at 37-75 °C (optimum 65 °C), at pH 6-8 (optimum pH 7.3) and in 1-5 % (w/v) NaCl (optimum 2.5-3.5 %). The isolate was aerobic but could also grow anaerobically using nitrate or elemental sulfur as electron acceptors. The strain was obligately heterotrophic, growing on complex organic substrates like yeast extract, Casamino acids, tryptone and peptone. Pyruvate, acetate, butyrate, sucrose, rhamnose and maltodextrin were used as complementary substrates. The G+C content of the genomic DNA was 68 mol%. Cells possessed characteristic phospholipids and glycolipids. Major fatty acids constituted saturated and unsaturated iso-branched and saturated anteiso-branched forms. Menaquinone 8 was the sole respiratory lipoquinone. Phylogenetic analysis of 16S rRNA gene sequences placed the strain in the family Thermaceae in the phylum 'Deinococcus-Thermus', which is consistent with the chemotaxonomic data. On the basis of phenotypic and phylogenetic data, strain 2M70-1(T) ( = JCM 15963(T)  = DSM 22268(T)) represents the type strain of a novel species of a novel genus, for which the name Rhabdothermus arcticus gen. nov., sp. nov. is proposed.