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 sgz302134T and sgz301742T, were isolated from paddy soil in Fujian Province. Strains sgz302134T and sgz301742T shared the highest 16S rRNA gene sequence similarities with the type strains Azospirillum isscasi C340-1T (98.2%) and Azospirillum thiophilum DSM 21654T (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 sgz302134T and sgz301742T 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 sgz302134T and sgz301742T contained Q-10 as the main quinone. The main fatty acids (>10%) of both strains were summed feature 2 (C12 : 0 aldehyde), summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and C16 : 0. The genomic DNA G+C content of strains sgz302134T and sgz301742T 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 sgz302134T (=MCCC 1K09520T=KCTC 8840T) and sgz301742T (=MCCC 1K09804T=KCTC 18149T), respectively.