Bioprospecting honeybee-derived Bacillus sp.: Metabolite profiling, antimicrobial, antifungal and antioxidant activities

Abstract

Background: The aim of this study is to characterize Bacillus sp. strains isolated from healthy honeybees (Apis mellifera) and the metabolites they produce in growth medium, and to ascertain their antimicrobial and antioxidant activities. Methods and results: With the characterization of Bacillus sp. strains, microscopy, resistance to harsh conditions, biochemical tests, antibiograms, antibacterial and antifungal activities were tested. Bacillus strains exhibited optimum growth at 35 °C, pH 8.0, 5% salt, and 20% glucose-containing medium. Antimicrobial activity of supernatants and extracts against Gram (+) bacteria and some fungi was observed. According to 16S rRNA sequence analysis, the isolates were determined to be similar to Bacillus sp. As a result of experiments with different solvents, ethyl acetate was used in purification and experiments because the extraction efficiency was higher. The chemical and structural properties of the 4 purified substances were determined by NMR analysis. These compounds (C₇H₁₃NO, C₁₂H₂₂O₁₁, C₁₈H₃₄O, C₈H₁₁NO) exhibited no antifungal efficacy; in contrast, C₁₂H₂₂O₁₁ and C₁₈H₃₄O displayed comparable antibacterial effects. C₁₈H₃₄O exhibited a much stronger antimicrobial effect due to its lower minimum inhibitory concentration (MIC) values, whereas C₁₂H₂₂O₁₁ showed relatively low activity. While C₇H₁₃NO was effective only against Escherichia coli, C₈H₁₁NO showed broad-spectrum activity against all bacterial species. It was determined that the liquid medium in which Bacillus sp. strains were grown had antioxidant activity. Conclusions: The isolated Bacillus sp. strains produce metabolites with significant antibacterial and antioxidant activities, suggesting their potential as sources of bioactive compounds, although no antifungal activity was detected.