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

Abstract

A Gram-positive, moderately halophilic, rod-shaped and facultatively anaerobic strain T66^T, was isolated from the rhizosphere soil of mangrove Acanthus ebracteatus in Guangxi, China. Strain T66^T 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^T to be closely related to Halobacillus litoralis SL-4 ^T (98.72%), Halobacillus dabanensis D-8 ^T (98.70%) and Halobacillus campisalis ASL-17 ^T (98.66%). The phylogenetic analysis based on the 16S rRNA gene sequence showed that strain T66^T belonged to the genus Halobacillus and formed a separate branch. The digital DNA-DNA hybridisation and average nucleotide identify values between strain T66^T 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_15:0 (68.4%) and anteiso-C_17:0 (13.4%). Phosphatidylglycerol, diphosphatidylglycerol, three unidentified phospholipids and an unidentified glycolipid were found in the polar lipid extraction. Strain T66^T could hydrolyse casein and contains several genes (e. g. vanY, vpr, pbpG and elpC) involved in protease. Therefore, strain T66^T 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^T represents a novel species of the genus Halobacillus, for which the name Halobacillus rhizosphaerae sp. nov. is proposed. The type strain is T66^T (= JCM 36534 ^T = MCCC 1K08701^T).