Comparative genome analysis of Alkalihalobacillus okhensis Kh10-101 T reveals insights into adaptive mechanisms for halo-alkali tolerance

Genomic insights into Marinospirillum alkalitolerans sp. nov., a novel PHB producing bacterium from an Indian impact crater, and an emended description of family Oceanospirillaceae

Two Gram-stain-negative bacterial strains (MEB164T and MEB148), were isolated from haloalkaline waters of Lonar, crater lake, India. The strains were helical, non-spore-forming and motile with polar tufts of flagella. Optimal growth occurred at 37 ℃, at pH 10 and with 3% (w/v) NaCl. 16S rRNA gene sequences of strains (MEB164T and MEB148) demonstrated the highest similarity with Marinospirillum alkaliphilum DSM 21637T (97.8%) followed by Marinospirillum celere DSM 18438T (96%). The genome size of strain MEB164T was determined to be 2.8 Mb with genomic DNA G + C contents of 53.1 mol %. ANI and dDDH values between strain MEB164T and the most closely related type strain M. alkaliphilum DSM 21637T were (72.3% and 21.4 ± 2.3%) while (AAI and POCP) values were (66.8 and 70.8%), respectively. Strain MEB164T exhibited potential for polyhydroxybutyrate (PHB) production, supported by key genes involved in PHB metabolism. Genome analysis further revealed presence of various pH tolerance genes, highlighting its adaptation to Lonar Lake. The predominant cellular fatty acids were summed feature 8 (C18:1 ω7c/C18:1 ω6c), C16:0 and summed feature 3 (C16:1 ω7c/C16:1 ω6c). The major respiratory quinone was ubiquinone-8. The prevalent polar lipids were diaminophosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified amino phospholipids, three unidentified phospholipids and one unidentified lipid. Polyphasic analysis suggests that the two strains constitute a novel species within the genus Marinospirillum (family Oceanospirillaceae), proposed as Marinospirillum alkalitolerans sp. nov. The type strain is MEB164T (= JCM 35957T = MCC 5207T = NCIMB 15458T) and MEB148 (= JCM 35956 = MCC 5212 = NCIMB 15459) is an additional strain.

Biochemical characterization of a novel oxidatively stable, halotolerant, and high-alkaline subtilisin from Alkalihalobacillus okhensis Kh10-101T

Halophilic and halotolerant microorganisms represent a promising source of salt-tolerant enzymes suitable for various biotechnological applications where high salt concentrations would otherwise limit enzymatic activity. Considering the current growing enzyme market and the need for more efficient and new biocatalysts, the present study aimed at the characterization of a high-alkaline subtilisin from Alkalihalobacillus okhensis Kh10-101^T . The protease gene was cloned and expressed in Bacillus subtilis DB104. The recombinant protease SPAO with 269 amino acids belongs to the subfamily of high-alkaline subtilisins. The biochemical characteristics of purified SPAO were analyzed in comparison with subtilisin Carlsberg, Savinase, and BPN'. SPAO, a monomer with a molecular mass of 27.1 kDa, was active over a wide range of pH 6.0-12.0 and temperature 20-80 °C, optimally at pH 9.0-9.5 and 55 °C. The protease is highly oxidatively stable to hydrogen peroxide and retained 58% of residual activity when incubated at 10 °C with 5% (v/v) H₂ O₂ for 1 h while stimulated at 1% (v/v) H₂ O₂ . Furthermore, SPAO was very stable and active at NaCl concentrations up to 5.0 m. This study demonstrates the potential of SPAO for biotechnological applications in the future.