Antifungal activity of streptavidin C1 and C2 against pathogens causing Fusarium wilt

Fusarium wilt is caused by the soil‐inhabiting fungus Fusarium oxysporum ff. spp. and is one of the most devastating plant diseases, resulting in losses and decreasing the quality and safety of agricultural crops. We recently reported the structures and biochemical properties of two biotin‐binding proteins, streptavidin C1 and C2 (isolated from Streptomyces cinnamonensis strain KPP02129). In the present study, the potential of the biotin‐binding proteins as antifungal agent for Fusarium wilt pathogens was investigated using recombinant streptavidin C1 and C2. The minimum inhibitory concentration of streptavidin C2 was found to be 16 µg ml–1 for inhibiting the mycelial growth of F. oxysporum f.sp. cucumerinum and F. oxysporum f.sp. lycopersici, while that of streptavidin C1 was found to be 64 µg ml–1. Compared with the nontreated control soil, the population density of F. oxysporum f.sp. lycopersici in the soil was reduced to 49·5% and 39·6% on treatment with streptavidin C1 (500 µg ml–1) and C2 (500 µg ml–1), respectively. A greenhouse experiment revealed that Fusarium wilt of tomato plants was completely inhibited on soil drenching using a 50‐ml culture filtrate of the streptavidin‐producing strain KPP02129. Significance and Impact of the Study: The present study reveals the potential of two biotin‐binding proteins, streptavidin C1 and C2 as antifungal agents for controlling Fusarium wilt of tomato plants. Streptavidin C1 and C2 suppressed the population density of Fusarium oxysporum f. sp. lycopersici in the soil under greenhouse conditions. Treatment with the culture filtrate of strain KPP02129 producing the streptavidins effectively controlled Fusarium wilt of tomato plants, and its effect was comparable to that of the commercial fungicide metconazole. This is the first study to evaluate the potential of biotin‐binding proteins as antifungal agents for controlling soil‐borne plant diseases.