Psychromonas boydii sp nov., a gas-vacuolate, psychrophilic bacterium isolated from an Arctic sea-ice core

A gas-vacuolate bacterium, strain 174(T), was isolated from a sea-ice core collected from Point Barrow, Alaska, USA. Comparative analysis of 16S rRNA gene sequences showed that this bacterium was most closely related to Psychromonas ingrahamii 37(T), with a similarity of >99%. However, strain 174(T) could be clearly distinguished from closely related species by DNA-DNA hybridization; relatedness values determined by two different methods between strain 174(T) and P. ingrahamii 37(T) were 58.4 and 55.7% and those between strain 174(T) and Psychromonas antarctica DSM 10704(T) were 46.1 and 33.1%, which are well below the 70% level used to define a distinct species. Phenotypic analysis, including cell size (strain 174(T) is the largest member of the genus Psychromonas, with rod-shaped cells, 8-18 mu m long), further differentiated strain 174(T) from other members of the genus Psychromonas. Strain 174(T) could be distinguished from its closest relative, P. ingrahamii, by its utilization of D-mannose and D-xylose as sole carbon sources, its ability to ferment myo-inositol and its inability to use fumarate and glycerol as sole carbon sources. In addition, strain 174(T) contained gas vacuoles of two distinct morphologies and grew at temperatures ranging from below 0 to 10 degrees C and its optimal NaCl concentration for growth was 3.5%. The DNA G + C content was 40 mol%. Whole-cell fatty acid analysis showed that 16 : 1 omega 7c and 16 : 0 comprised 44.9 and 26.4% of the total fatty acid content, respectively. The name Psychromonas boydii sp. nov. is proposed for this novel species, with strain 174(T) (=DSM 17665(T) =CCM 7498(T)) as the type strain.