A novel haloalkaliphilic bacterium, designated G-116T, was isolated from the decaying biomass of a laboratory culture of cyanobacterium Geitlerinema species. Cells of strain G-116T were Gram-stain-negative, motile spirilla. Strain G-116T showed high halotolerance to 20 % (w/v) NaCl (optimum growth at 3.5-6.0 %, w/v) and obligately alkaliphilic growth within the pH range 7.3-10.4 (optimum growth at pH 8.7-8.9). The major fatty acids identified were C16:0, summed feature 8 (C18:1 ω7c/C18 :1 ω6c), summed feature 3 (C16:1 ω7c/C16 :1 ω6c) and C19:0 cyclo ω8c. The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, an unidentified phospholipid, three unidentified amino lipids and five unidentified lipids. The predominant respiratory quinone was ubiquinone-8 (Q-8). The G+C content of the genomic DNA was 60.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the closest genus with a validly published name is a monotypic Salinispirillum and strain G-116T clustered with Salinispirillum marinum GCWy1T with a 16S rRNA gene sequence similarity of 94.3 %. Based on the data obtained from phenotypic and chemotaxonomic studies and the phylogenetic analysis, the isolate is proposed to be a representative of a novel genus and a novel species, Natronospirillum operosum gen. nov., sp. nov. Together with S. marinum they form a separate clade, for which a novel family, Natronospirillaceae fam. nov., is proposed. In addition, Saccharospirillaceae fam. nov. and Gynuellaceae fam. nov. are proposed to encompass the genera Saccharospirillum and Reinekea, and the genus Gynuella, respectively. All three novel families are within the order Oceanospirillales of the class Gammaproteobacteria. The type strain of the type species, Natronospirillum operosum gen. nov., sp. nov. is G-116T (=VKM B-3134T=KCTC 62956T).
Keywords: Geitlerinema; Gynuella; Natronospirillum; Reinekea; Saccharospirillum; Salinispirillum.