A total of 23 sulfur-oxidizing bacterial (SOB) isolates were recovered from the rhizosphere of onion plants (Allium cepa L.), among which isolates B12 and B15 demonstrated the highest sulfur-oxidizing potential. These two isolates markedly reduced the pH of the growth medium from 8.38 to 7.01 and 7.12, respectively, even in the absence of glucose, indicating strong sulfur-oxidizing capacity. Molecular identification based on 16S rRNA gene sequencing revealed that B12 corresponds to Bacillus spizizenii strain B566 (GenBank Accession number PX437460 with 99% similarity), while B15 corresponds to Priestia aryabhattai strain B567 (GenBank Accession number PX437823 with 99% similarity). Both strains exhibited progressive sulfate accumulation with incubation time. After one week, sulfate concentrations reached 119.9 and 696.7 mg SO₄²⁻ L⁻¹ for the two strains, respectively. Additionally, both isolates were capable of synthesizing the plant growth hormone indole-3-acetic acid (IAA) at concentrations of 141.9 µg/mL for B. spizizenii and 116.6 µg/mL for P. aryabhattai when cultivated in tryptophan-enriched medium. These findings highlight the potential application of B. spizizenii and P. aryabhattai as biofertilizer candidates to enhance sulfur availability and promote plant growth in sustainable agricultural systems.