Inhibition of Alternaria alternata biofilms and invitro antifungal efficacy of [Glu, Asp] surfactin-C and its divalent metal-ion complexes.

[Glu1, Asp5] surfactin-C, a lipopeptide biosurfactant, and its divalent metal ion complexes were investigated for their antifungal and antibiofilm activities against Alternaria alternata, a pathogen causing early blight in tomato plants. The study employed various techniques, including the Poison food technique and biofilm inhibition assays. Results demonstrated that surfactin-C exhibits dose-dependent antifungal properties, with its efficacy significantly enhanced by divalent metal ion complexation. Zn (II)-Surfactin-C showed the highest mycelial growth inhibition (85.88 %) and lowest disease severity index in tomato leaves (42.76 %) and roots (37.92 %). The antifungal activity ranked as follows: Zn (II) > Cu (II) > Ca (II) > Mg (II) > Surfactin-C alone. Minimum Inhibitory Concentration (MIC) values ranged from 300 μg/ml for surfactin-C to 50 μg/ml for Cu (II)-Surfactin-C with IC values of 177.89 to 25.69 respectively, indicating superior efficacy of the metal complexes. Antibiofilm activity followed a similar trend, with Cu (II) slightly higher than Zn (II) complexes showing the highest potency. Computational studies suggested that the acidic amino acids (glutamic and aspartic) play a crucial role in the antibiofilm activity of [Glu1, Asp5] surfactin-C. These findings highlight the potential of surfactin-C-metal ion complexes, particularly with copper and zinc, as effective biocontrol agents against A. alternata in tomato plants.