Bacillus alkalidiazotrophicus sp. nov., a diazotrophic, low salt-tolerant alkaliphile isolated from Mongolian soda soil.

Strain MS 6T was obtained from a microoxic enrichment with a soda soil sample from north-eastern Mongolia in nitrogen-free alkaline medium at pH 10. The isolate had clostridia-like motile cells and formed ellipsoid endospores. It was able to fix dinitrogen gas growing on nitrogen-free alkaline medium. Strain MS 6T was a strictly fermentative bacterium without a respiratory chain, although it had a high catalase activity and tolerated aerobic conditions. It was an obligate alkaliphile with a pH range for growth between 7.5 and 10.6 (optimum at 9.0–9.5). Growth and nitrogen fixation at pH 10 were possible at a total salt content of up to 1.2 M Na+ (optimum at 0.2–0.3 M). The dominant cellular fatty acids included C16 : 0, C16 : 1 ω7, anteiso-C15 : 0 and C14 : 0. The dominant isoprenoid quinone was MK-7. The cell-wall peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. 16S rRNA gene sequencing identified strain MS 6T as a member of the genus Bacillus. Its closest relative was Bacillus arseniciselenatis E1HT. The key functional nitrogenase gene nifH was detected in both strain MS 6T and its close relative and these strains formed a novel lineage in the nifH gene family. On the basis of these phenotypic and genetic comparisons, strain MS 6T is proposed to represent a novel species of the genus Bacillus, Bacillus alkalidiazotrophicus sp. nov. with the type strain MS 6T (=NCCB 100213T=UNIQEM U377T).