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 <i>Fontibacillus forbon</i> sp. nov., with strain BL-9^T as the type strain, was isolated from the rhizosphere of <i>Fraxinus chinensis</i>. 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 <i>Fontibacillus phaseoli</i> BAPVE7B (98.03%), followed by <i>Fontibacillus solani</i> A4STR04 (96.72%), <i>Fontibacillus panacisegetis</i> (96.6%), <i>Paenibacillus vini</i> (96.6%), and <i>Paenibacillus segetis</i> DB13260 (96.57%). The phylogenomic tree supported that strain BL-9^T was most closely related to <i>F. phaseoli</i> BAPVE7B. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) between strain BL-9^T and its closely related type strain, <i>F. phaseoli</i> 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 <i>nif</i> (<i>ni</i>trogen <i>f</i>ixation) gene cluster containing 10 genes (<i>nifB nifH nifD nifK nifE nifN nifX orf1 hesA nifV</i>). 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 <i>Fontibacillus</i> 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 <i>Fontibacillus.</i> The name proposed for this species is <i>Fontibacillus forbon</i> sp. nov., with the type strain BL-9^T.