Description of two nitrogen-fixing bacteria, Azospirillum mesophilum sp. nov. and Azospirillum terrae sp. nov., isolated from paddy soils

Two novel aerobic, rod-shaped, motile bacterial strains, designated as sgz302134 T and sgz301742 T , were isolated from paddy soil in Fujian Province. Strains sgz302134 T and sgz301742 T shared the highest 16S rRNA gene sequence similarities with the type strains Azospirillum isscasi C340-1 T (98.2%) and Azospirillum thiophilum DSM 21654 T (97.4%), respectively. The phylogenetic tree based on 16S rRNA gene sequences showed that two strains clustered with members of the genus Azospirillum . Growth of strains sgz302134 T and sgz301742 T was observed at 10–45 °C, pH 5.0–9.5 and 0–0.5% (w/v) NaCl and 15–37 °C, pH 6.0–9.0 and 0–1.0% (w/v) NaCl, respectively. Strains sgz302134 T and sgz301742 T contained Q-10 as the main quinone. The main fatty acids (>10%) of both strains were summed feature 2 (C 12 : 0 aldehyde), summed feature 3 (C 16 : 1 ω 7 c and/or C 16 : 1 ω 6 c ), summed feature 8 (C 18 : 1 ω 7 c and/or C 18 : 1 ω 6 c ) and C 16 : 0 . The genomic DNA G+C content of strains sgz302134 T and sgz301742 T was 68.4 and 68.3%, respectively. The digital DNA–DNA hybridization and average nucleotide identity values between the two strains and their related reference strains were 27.8 and 87.4% and 22.0 and 84.3%, respectively. Both strains possessed nif genes nifBDEHKN . Based on the above results, these two strains represent two novel species of the genus Azospirillum , for which the names Azospirillum mesophilum sp. nov. and Azospirillum terrae sp. nov. are proposed. The type strains are sgz302134 T (=MCCC 1K09520 T =KCTC 8840 T ) and sgz301742 T (=MCCC 1K09804 T =KCTC 18149 T ), respectively.