Halomonas rifensis sp. nov., an exopolysaccharide-producing, halophilic bacterium isolated from a solar saltern

A polyphasic taxonomic study was conducted on strain HK31(T), a moderately halophilic bacterium isolated from a solar saltern in Chefchaouen, Morocco. The strain was a Gram-reaction-negative, oxidase-positive rod, which was motile by means of peritrichous flagella. The strain required NaCl for growth and grew in salt concentrations (mixture of sea salts) of 0.5-20 % (w/v) (optimum 5-7.5 %, w/v), at 25-45 °C (optimum 32 °C) and at pH 5-10 (optimum pH 6-9). Strain HK31(T) did not produce acids from sugars and its metabolism was respiratory, using oxygen as terminal electron acceptor. The strain was positive for the accumulation of poly-β-hydroxyalkanoate granules and formed mucoid colonies due to the excretion of an exopolysaccharide. The DNA G+C content was 61.5 mol%. 16S rRNA gene sequence analysis indicated that it belonged to the genus Halomonas in the class Gammaproteobacteria. The most phylogenetically related species was Halomonas anticariensis, with which strain HK31(T) showed a 16S rRNA gene sequence similarity of 96.48 %. Its major fatty acids were C(18 : 1)ω7c, C(16 : 0), C(19 : 0) cyclo ω8c, C(16 : 1)ω7c/iso-C(15 : 0) 2-OH and C(12 : 0) 3-OH and the predominant respiratory lipoquinone was ubiquinone with nine isoprene units (Q-9). Based on the evidence provided in this study, strain HK31(T) (= CECT 7698(T) = LMG 25695(T)) represents a novel species of the genus Halomonas, for which the name Halomonas rifensis is proposed.