Physiological characterization of a novel strain within Rhodobacteraceae, isolated from a biofilm sample on a barite chimney at the Loki´s Castle Vent Field.

Abstract

Strain M was isolated from a biofilm found on top of one of the barite chimney at Loki´s Castle Vent Field (73°30´N and 8°E) in the Norwegian-Greenland Sea. A polyphasic characterization, including physical and phylogenetic parameters, was performed, showing that strain M represents a novel species in the Roseobacter group within Alphaproteobacteria. The 16s rRNA gene sequence comparisons showed that strain M had 95.68 % similarity to the closest relative within the Roseobacter group. Cells were motile and rod-shaped, grew at temperatures between 10-40 °C (optimum 27-35 °C), in a pH range of 5.5- 8 (optimum 6.5-7.5), NaCl concentration range of 0.5-5 % (optimum 2 %), and pressure optimum at 300 bar. Mg2+ was not a requirement for the growth. Strain M showed positive oxidase and catalase activity. The strain grew aerobically and microaerobically with oxygen as terminal electron acceptor, but could also utilize nitrate as terminal electron acceptor under anaerobic conditions. Nitrate was reduced to nitrite under anaerobic and aerobic conditions. Strain M could utilize a broad range of monosaccharides, disaccharides, carboxylic acids, peptides and other organic substrates as a carbon source. Strain M grew in the presence of kanamycin, rifampicin and erythromycin. Q10 was the sole respiratory menaquinone. The fatty acids profile was dominated by 18:1 7c, and the polar lipids detected were phosphatidylethanolamine, phosphatidylcholine and phosphatidylglycerol. This study suggests that the amount of organic rich substrates available for microbes at the Loki´s Castle Vent Field is sufficient to support a heterotrophic lifestyle, and that strain M could participate in the carbon cycle by decomposing simple carbon sources produced in this environment. Together with the ability to grow in aerobic, microaerobic and anaerobic conditions, strain M could inhabit and exploit different niches within the microbial mat. With the reduction of nitrate to nitrite, strain M might also play a role in the nitrogen cycle at Loci´s Castle Vent Field through a denitrification process. Based on its phylogenetic and phenotypic properties, strain M is considered to represent a new species within the group Roseobacter within the family Rhodobacteraceae.