Bacillus siamensis CCT8089: a novel phosphate-solubilizing bacterium enhancing maize and soybean growth

Phosphorus (P) is an essential macronutrient for plant growth, but its availability in tropical soils is limited due to fixation by iron and aluminum oxides. This study aimed to characterize the Bacillus siamensis CCT8089 strain in vitro, evaluating its phosphate-solubilizing and plant growth-promoting abilities and its agronomic potential in maize and soybean crops. In vitro, CCT8089 tolerated osmotic stress, produced exopolysaccharides and biofilm, and demonstrated compatibility with commercial inoculants (Azospirillum brasilense and Bradyrhizobium japonicum). The strain also exhibited biocontrol activity against Macrophomina phaseolina and Sclerotinia sclerotiorum. CCT8089 produced organic acids, particularly malic and acetic acid in Ca₃(PO₄)₂, while gluconic acid and lactic acid were predominant in FePO₄ and AlPO₄, respectively. Additionally, CCT8089 produced indole-3-acetic acid (IAA) and significantly increased root biomass in greenhouse experiments. In field trials, CCT8089 applied via seed treatment or furrow application significantly increased yield and phosphorus acquisition efficiency in maize and soybean compared to the non-inoculated control (83.25 kg P₂O₅). Furrow application was more effective for maize, while no significant differences were observed between application methods in soybean. Notably, CCT8089 demonstrated greater yield stability across different environmental conditions, with the best performance observed at 200 mL/ha in-furrow application and 100 mL per 60,000 seeds (maize) or 50 kg of seeds (soybean) for seed treatment. These results highlight the potential of strain CCT8089 as a novel inoculant for maize and soybean crops, with viable application through both seed treatment and furrow application.