Hypnocyclicus thermotrophus gen. nov., sp nov isolated from a microbial mat in a hydrothermal vent field

The bacterial strain, IR-2(T), was isolated from a microbial mat sampled, near a hydrothermal vent in the Greenland Sea. Phylogenetic analysis, based on the 16S rRNA gene, showed that the closest relatives of IR-2(T) were Ilyobacter tartaricus, Ilyobacter insuetus, Propionigenium modestum and Fusobacterium varium (91 % 16S rRNA gene sequence similarity). The cells of the novel strain were Gram-stain-negative and pleomorphic; changing from long motile rods to non-motile ring structures during the growth cycle. Growth occurred at 20-55 degrees C (optimally at 48 degrees C), with 1-6% (w/v) NaCl (optimally with 2 %), and at pH 5.3-8.0 (optimally at pH 6.0-8.0). The strain had obligate fermentative growth on various sugars and yeast extract. The DNA G+C content of strain IR-2(T) was 25.7 mol%. The cell sugars comprised mainly ribose, mannose and glucose, while the main polar lipids were glycolipids, phospholipids, phosphatidylglycerol and diphosphatidylglycerol. The fatty acid content of strain IR-2 was dominated by saturated and unsaturated iso-branched or anteiso-branched forms. Strain IR-2 represents a novel genus and species, for which the name Hypnocyclicus thermotrophus gen. nov., sp. nov. is proposed. The type strain is IR-2(T) (=DSM 100055=JCM 30901).