Rhizobium setariae sp. nov., an Indole-3-Acetic Acid-Producing Bacterium Isolated from Green Foxtail, Setaria viridis.

Abstract

A Gram-negative, indole-3-acetic acid-producing, aerobic, motile strain, designated as KVB221T, was isolated from a green foxtail plant, Setaria viridis, from a park near the coast of Haeundae Beach, Busan, Republic of Korea. The 16S rRNA gene analysis revealed strain KVB221T to be a member of the genus Rhizobium, from which Rhizobium alvei TNR-22T (97.2%), Rhizobium daejeonense L61T (96.9%), and Rhizobium ipomoeae shin9-1T (95.7%) were selected for comparative analysis. Growth of the strain was observed at 10-50°C (optimum 25-30°C), at pH 5-10 (optimum pH 7), and in the presence of 0-8% NaCl (optimum 0%). The strain was observed to produce 36.3 ± 0.8μg/ml of indole following 5 days of incubation. The major fatty acids are comprised of C16:0, C19:0 cyclo ω8c, C18:1 ω7c, and the unresolved group summed feature 8 (C18:1 ω7c and/or C18:1 ω6c), while major polar lipids are identified as phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylmonomethylethanolamine (PME). The predominant quinone is Q-10 and the DNA G+C content of the strain is 59.3%. Based on publicly available genome data between strain KVB221T and its closely related strains, the average nucleotide identity and in silico DNA-DNA hybridization values ranged from 72.7 to 73.1 and 19.7 to 20.4%, respectively. Based on the chemotaxonomic, phenotypic, and genomic comparisons reported here, we propose Rhizobium setariae sp. nov. as a novel species belonging to the genus Rhizobium. The type strain is KVB221T (= KACC 21713T = NBRC 114644T).