Biosurfactant Production and Antifungal Potential of Bacterial Isolates for Biocontrol of Phytopathogens

Abstract

Biotic stress from phytopathogens like bacteria, fungi, yeasts, and insect pests significantly reduces plant yields. Biocontrol agents and their active compounds offer a sustainable approach to managing these pathogens. In this study, four bacterial isolates Bacillus cereus, B. anthracis, B. velezensis, and Serratia marcescens were screened for biosurfactant production using foam formation, oil spreading and emulsification activity assays. B. velezensis exhibited the highest foam stability and emulsification activity (E24%). Notably, the maximum growth observed in B. anthracis (OD 1.247±0.002 at 108 h) did not correlate directly with biosurfactant production, indicating that higher bacterial growth does not necessarily lead to increased biosurfactant synthesis. Biosurfactant yields varied across different media: ​Luria-Bertani (LB) medium: B. velezensis produced 0.349±0.004 g/50 mL, followed by B. anthracis (0.215±0.001 g/50 mL), B. cereus (0.210±0.004 g/50 mL), and S. marcescens (0.206±0.003 g/50 mL). Nutrient Broth (NB) medium: S. marcescens yielded the highest biosurfactant production at 0.277±0.001 g/50 mL, with B. velezensis (0.256±0.003 g/50 mL), B. anthracis (0.239±0.003 g/50 mL), and B. cereus (0.230±0.005 g/50 mL) following.​ Potato Dextrose Broth (PDB) medium: B. velezensis again led with 0.316±0.001 g/50 mL, trailed by S. marcescens (0.278±0.004 g/50 mL), B. anthracis (0.262±0.005 g/50 mL), and B. cereus (0.238±0.003 g/50 mL).​ The antifungal efficacy of the biosurfactants was assessed on Potato Dextrose Agar (PDA) plates. B. velezensis demonstrated the highest inhibition percentages against several phytopathogens: Rhizoctonia solani (88.44%), Fusarium udum (82.96%), Helminthosporium maydis (72.68%), F. oxysporum f. sp. Lycopersici (68.07%) and Fusarium solani (68.07%). These findings suggest that B. velezensis biosurfactant is particularly effective against the tested phytopathogens and holds promise as a biocontrol agent in sustainable agriculture.