Isolation and Identification of Bacillus velezensis G52 and Its Growth-Promoting Mechanism on Navel Orange Seedlings

This study isolated and screened a multifunctional plant-growth-promoting bacterium, Bacillus sp. G52, from the rhizosphere soil of Gannan navel oranges. Through pot experiments and genomic analysis, the growth-promoting effects and molecular mechanisms of strain G52 on navel orange seedlings were systematically evaluated. The results showed that strain G52 could secrete indole-3-acetic acid (IAA, yield: 18.68 ± 0.81 mg/L), siderophores (yield: 47.10 ± 1.03%), and phosphate-solubilizing substances (91.85 ± 4.94 mg/L) while also exhibiting ACC deaminase activity and ammonia production. Pot experiments demonstrated that inoculation with G52 significantly increased seedling height (12.51%), stem diameter (10.97%), biomass (27.87% in shoots, 41.13% in roots), and chlorophyll content (37.40% increase in total chlorophyll). Additionally, G52-treated seedlings showed enhanced antioxidant enzyme activities (SOD, POD, CAT), indicating improved stress resistance. Genomic analysis revealed that G52 carries functional genes related to IAA synthesis (e.g., trpA-trpF) and siderophore production (e.g., ent gene cluster), further confirming the molecular basis of its growth-promoting potential. Phylogenetic analysis indicated a 99.7% similarity between G52 and Bacillus velezensis. This study provides a theoretical foundation for developing multifunctional Bacillus-based biofertilizers, contributing to sustainable agricultural development.