In vitro effects of Bacillus velezensis strain Mandacaium against Xanthomonas citri pv. glycines: genomic and metabolomic insights

Biological agents offer an alternative to chemical pesticides in managing plant diseases, as they help decrease environmental contamination and reduce selective pressure for resistant pathogens. In this study, bacteria isolated from the larval food of stingless bees were tested for in vitro antibacterial activity against Xanthomonas citri pv. glycines, the cause of soybean bacterial pustule. A strain identified as Bacillus velezensis showed notable growth inhibition in agar diffusion tests. Fractionation of the bacterial culture supernatant revealed that antimicrobial activity was concentrated in the metabolic fraction, especially in the ethyl acetate extract, which exhibited a concentration-dependent inhibition (CDI) of 0.015 mg/mL against X. citri pv. glycines. A phytotoxicity test using soybean seeds indicated no immediate effects on germination under experimental conditions. LC-MS analysis of the bioactive fraction tentatively identified 15 metabolites, mainly diketopiperazines, although other molecular features remained unknown. Whole-genome sequencing showed a genome size of about 4.0 Mb and 13 predicted biosynthetic gene clusters, including those likely involved in lipopeptide and polyketide production; however, these compounds were not detected in the analyzed extract. These findings demonstrate in vitro antibacterial activity linked to metabolites produced by a newly characterized Bacillus velezensis strain mandacaium and outline its biosynthetic potential at the genomic level. The results lay the groundwork for future in planta research to assess its role in sustainable plant disease management.