Aquibacillus halophilus gen. nov., sp. nov., a moderately halophilic bacterium from a hypersaline lake, and reclassification of Virgibacillus koreensis as Aquibacillus koreensis comb. nov. and Virgibacillus albus as Aquibacillus albus comb. nov.

Abstract

A novel Gram-stain-positive, moderately halophilic bacterium, designated strain B6BT, was isolated from the water of an Iranian hypersaline lake, Aran-Bidgol, and characterized taxonomically using a polyphasic approach. Cells of strain B6BT were rod-shaped, motile and produced ellipsoidal endospores in terminal positions in non-swollen sporangia. Strain B6BT was a strictly aerobic bacterium and catalase- and oxidase-positive. The strain was able to grow at NaCl concentrations of 0.5–20.0 % (w/v), with optimum growth occurring at 10.0 % (w/v) NaCl. The optimum temperature and pH for growth were 35 °C and pH 7.0. On the basis of 16S rRNA gene sequence analysis, strain B6BT was shown to belong to the phylum Firmicutes and its closest phylogenetic similarities were with the species Virgibacillus koreensis BH30097T (97.5 %), Virgibacillus albus YIM 93624T (97.4 %), Sediminibacillus halophilus EN8dT (96.8 %), Sediminibacillus albus NHBX5T (96.6 %), Virgibacillus carmonensis LMG 20964T (96.3 %) and Paraliobacillus quinghaiensis YIM-C158T (96.0 %), respectively. Phylogenetic analysis revealed that strain B6BT, along with V. koreensis BH30097T and V. albus YIM 93624T, clustered in a separate clade in the family Bacillaceae . The DNA G+C content of the novel isolate was 35.8 mol%. DNA–DNA hybridization experiments revealed low levels of relatedness between strain B6BTand V. koreensis BH30097T (13 %) and V. albus YIM 93624T (33 %). The major cellular fatty acid of strain B6BT was anteiso-C15 : 0 (75.1 %) and its polar lipid pattern consisted of phosphatidylglycerol, diphosphatidylglycerol, an unknown phospholipid and an unknown glycolipid. The isoprenoid quinones were MK-7 (90 %) and MK-6 (3 %). The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. All of these features support the placement of isolate B6BT within the phylum Firmicutes . It is closely related to V. koreensis and V. albus , but with features that clearly distinguish it from species of the genus Virgibacillus or of other related genera. On the basis of the polyphasic evidence derived in this study, we propose that strain B6BT be placed within a new genus, as Aquibacillus halophilus gen. nov., sp. nov., with B6BT as the type strain ( = IBRC-M 10775T = KCTC 13828T). We also propose that V. koreensis and V. albus should be transferred to this new genus and be named Aquibacillus koreensis comb. nov. and Aquibacillus albus comb. nov., respectively. The type strain of Aquibacillus koreensis comb. nov. is BH30097T ( = KCTC 3823T = IBRC-M 10657T = JCM 12387T) and the type strain of Aquibacillus albus comb. nov. is YIM 93624T ( = DSM 23711T = IBRC-M 10798T = JCM 17364T).