Two strictly anaerobic nitrogen-fixing strains, designated RG17T and RG53T, were isolated from paddy soils in China. Strains RG17T and RG53T showed the highest 16S rRNA gene sequence similarities to the type strain Geomonas paludis (97.9-98.4%). Phylogenetic tree based on 16S rRNA gene sequences showed that two strains clustered with members of the genus Geomonas. Growth of strain RG17T was observed at 20-42 °C, pH 5.5-8.5 and 0-0.3% (w/v) NaCl while strain RG53T growth was observed at 20-42 °C, pH 5.5-9.5 and 0-0.7% (w/v) NaCl. Strains RG17T and RG53T contained MK-8 as main menaquinone and C15:1 ω6c, iso-C15:0, and Summed Feature 3 as the major fatty acids. The genomic DNA G + C content of strains RG17T and RG53T were 61.6 and 60.7%, respectively. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the isolated strains and the closely related Geomonas species were lower than the cut-off value (dDDH 70% and ANI 95-96%) for prokaryotic species delineation. Both strains possessed nif genes nifHDK and nitrogenase activities. Based on the above results, the two strains represent two novel species of the genus Geomonas, for which the names Geomonas fuzhouensis sp. nov. and Geomonas agri sp. nov., are proposed. The type strains are RG17T (= GDMCC 1.2687T = KTCC 25332T) and RG53T (= GDMCC 1.2630T = KCTC 25331T), respectively.
Keywords: Geomonas agri; Geomonas fuzhouensis; Nitrogen fixation; Paddy soil.
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