Halobacillus rhizosphaerae sp. nov., a moderately halophilic bacterium with protease activities isolated from the rhizosphere soil of the mangrove Acanthus ebracteatus.

A Gram-positive, moderately halophilic, rod-shaped and facultatively anaerobic strain T66, was isolated from the rhizosphere soil of mangrove Acanthus ebracteatus in Guangxi, China. Strain T66 was observed to grow at 15-40 ℃ (optimum 30 ℃), pH 5-8 (optimum 6-7) and with 2-20% (w/v) NaCl (optimum 6%). The phylogenetic tree of the 16S rRNA gene sequences depicted a cluster of strain T66 to be closely related to Halobacillus litoralis SL-4 (98.72%), Halobacillus dabanensis D-8 (98.70%) and Halobacillus campisalis ASL-17 (98.66%). The phylogenetic analysis based on the 16S rRNA gene sequence showed that strain T66 belonged to the genus Halobacillus and formed a separate branch. The digital DNA-DNA hybridisation and average nucleotide identify values between strain T66 and its related species were 17.80-19.80% and 70.78-73.22%, respectively, which were lower than the threshold recommended for species delineation. The genomic DNA G + C content was 40.9%. The predominant isoprenoid quinone was MK-7, the cell-wall peptidoglycan contained meso-diaminopimelic acid, and the major fatty acids that accounted for more than 10.0% were anteiso-C (68.4%) and anteiso-C (13.4%). Phosphatidylglycerol, diphosphatidylglycerol, three unidentified phospholipids and an unidentified glycolipid were found in the polar lipid extraction. Strain T66 could hydrolyse casein and contains several genes (e. g. vanY, vpr, pbpG and elpC) involved in protease. Therefore, strain T66 is salt-tolerant and produces protease, and it may have development and utilisation value in flavouring agents and food curing. Based on phenotypic, chemotaxonomic data and genotypic characteristics, strain T66 represents a novel species of the genus Halobacillus, for which the name Halobacillus rhizosphaerae sp. nov. is proposed. The type strain is T66 (= JCM 36534 = MCCC 1K08701).