Investigation of Siderophore production and Antifungal activity against Phytophthora capsici as related to Iron (III) nutrition by Lysobacter antibioticus HS124

Lysobacter antibioticus HS124 isolated from pepper rhizosphere soil produced catechol type siderophore. Purified siderophore by Diaion HP-20 and silica gel column chromatography showed several hydroxyl functional groups adjacent to benzene rings by analysis of $^1H$ NMR spectroscopy. The strain HS124 showed different activities to suppress Phytophthora capsici with different concentrations of exogenous Fe (III) in minimal medium where antifungal activity with $100{\mu}M$ Fe (III) was approximately 1.5 times higher than in absence of Fe (III). Bacterial population in this Fe (III)-amended medium was also highest with $8.9{\times}10^8\;CFU\;ml^{-1}$ which also corresponded to the strongest siderophore activity. When grown in rich medium (minimal medium with N, $P_2O_5K_2O$ and glucose), HS124 exhibited approximately 2 times stronger antifungal activity compared to minimal medium. In pot trials, treatments of bacterial culture grown in rich medium with (C1) or without (C2) $100{\mu}M$ Fe (III) exhibited a high protection of pepper plants from disease, compared to medium only with (M1) or without (M2) $100{\mu}M$ Fe (III). Especially, treatment C1 showed the best disease control effect of about 70 %. Thus, the strain HS124 should be recommended as a potential biocontrol agent against P. capsici in pepper.