N₂-Fixing Fontibacillus forbon sp. nov., a Novel Species from the Plant Rhizosphere

N₂-fixing bacteria have great potential to be used as biofertilizer in agriculture to promote plant growth via nitrogen fixation. In this study, a novel species Fontibacillus forbon sp. nov., with strain BL-9^T as the type strain, was isolated from the rhizosphere of Fraxinus chinensis. Strain BL-9^T was able to fix nitrogen and grow on nitrogen-free medium. Phylogenetic analysis of 16S rRNA gene revealed that strain BL-9^T was most closely related to Fontibacillus phaseoli BAPVE7B (98.03%), followed by Fontibacillus solani A4STR04 (96.72%), Fontibacillus panacisegetis (96.6%), Paenibacillus vini (96.6%), and Paenibacillus segetis DB13260 (96.57%). The phylogenomic tree supported that strain BL-9^T was most closely related to F. phaseoli BAPVE7B. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) between strain BL-9^T and its closely related type strain, F. phaseoli BAPVE7B, were 42.5% and 90.94%, respectively, which were below the values (70% for dDDH and 95% for ANI) for species discrimination. The DNA G+C content of strain BL-9^T was 49.7%. The genome of strain BL-9^T had a nif (nitrogen fixation) gene cluster containing 10 genes (nifB nifH nifD nifK nifE nifN nifX orf1 hesA nifV). The predominant fatty acid was anteiso-C15:0, the major menaquinone was MK-7, and the major polar lipid was diphosphatidylglycerol. Strain BL-9^T and its closely related species of Fontibacillus had some common and distinguished physiological characteristics. Based on genomic, phylogenetic, chemotaxonomic, and phenotypic features, strain BL-9^T represents a novel species of the genus Fontibacillus. The name proposed for this species is Fontibacillus forbon sp. nov., with the type strain BL-9^T.