Strain MS 6 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 6 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 C, C 7, anteiso-C and C. 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 6 as a member of the genus . Its closest relative was E1H. The key functional nitrogenase gene was detected in both strain MS 6 and its close relative and these strains formed a novel lineage in the gene family. On the basis of these phenotypic and genetic comparisons, strain MS 6 is proposed to represent a novel species of the genus , sp. nov. with the type strain MS 6 (=NCCB 100213=UNIQEM U377).

Keyword(s): NF, nitrogen fixation

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