Aluminum toxicity is a major problem for the growth of plants in acidic soils. Plant growth-promoting rhizobacteria such as Bacillus toyonensis Bt04 offer promising solutions to alleviate such stress through hormonal modulation and improved stress tolerance. This study investigated the ability of Bt04 to mitigate aluminum toxicity in maize roots and its interaction with auxin transport. Efflux inhibitor 1-N-naphthylphthalamic acid (NPA) and influx inhibitor 1-naphthoxyacetic acid (1-NOA) were applied to assess their effects on stress phytohormone dynamics and aluminum accumulation. Bt04 inoculation reduced aluminum accumulation in root tissues, particularly in the transition zone, which is consistent with the improvement of root barrier functions or exclusion mechanisms. Hormone profiling revealed that Bt04 produced significant quantities of salicylic and benzoic acid (3000 and 15,430 pmol g-1DW, respectively), while abscisic acid (ABA) and jasmonic acid (JA) productions were low. Auxin transport modulation showed distinct effects on root hormone profiles. NPA suppressed ABA level, whereas 1-NOA enhanced its accumulation by 124% under stress. Bt04 amplified or reversed these effects depending on the type of co-treatment, highlighting its regulatory role in hormonal homeostasis. JA levels increased after NPA treatment, reaching 13,323 pmol g-1DW, but were reduced by 81% when Bt04 was co-applied. Bt04 together with 1-NOA increased JA and JA-Ile under stress, respectively by 81% and 159%, indicating a stress-specific synergy. These results demonstrate that Bt04 mitigates aluminum toxicity by modulating hormonal crosstalk and auxin transport, making it a potential tool for use in biofertilization strategies to improve crop resilience in acidic, aluminum-affected soils.