Isolation of a novel halothermophilic strain of the genus Gracilibacillus from Howz-e Sultan hypersaline lake in Iran

Background and Objectives: Halothermophilic bacteria are adapted to high osmolarity and can grow in high saline environments and high temperatures. This study was aimed at the isolation of halothermophilic bacteria from Howz-e Sultan hypersaline lake in the central desert zone in Iran. Materials and Methods: Samples were collected and after preparing dilutions, the samples were cultured on Molten haloid agar with different salt concentrations (5-35%), then the plates were incubated at 35-70ºC in both aerobic and anaerobic conditions. Biochemical characterizations, utilization of carbon sources, production of exoenzymes and antibiotic susceptibility were investigated. Taxonomic and phylogenetic analyses were performed using 16S rRNA gene sequences. Results: One of the isolated bacteria was found to be Gram-positive, hyperhalophilic, thermophilic, endospore-forming, and was named as 1-9 h isolate. The bacterial cells were bacilli-shaped, which produced endospores at a subterminal position. This isolate was an aerobe and facultative anaerobe and grew between pH 5.0 and 10.0 (optimal growth at pH 7.0-7.5), at temperature between 15°C and 65°C (optimal growth at 40-45°C) and at salinity of 9-32% (w/v) NaCl, growing optimally at 18% (w/v) NaCl. On the basis of 16S rRNA gene sequence analysis, isolate 1-9 h belongs to the genus Bacillus within the phylum Firmicutes and showed the closest phylogenetic similarity to Gracilibacillus sp. IBP-V003 (99.0%). Conclusion: Based on the results of its phenotypic and genotypic properties, strain 1-9 h represents a novel strain of the genus Gracilibacillus. It can be used in various fields of industry and biotechnology