Secondary metabolites from Lysobacter enzymogenes isolate LEC possess suppressive activity against microbial plant pathogens in vitro and in planta

Abstract In previous studies Lysobacter enzymogenes isolate LEC exhibited broad biocontrol activity against microbial phytopathogens on different crops. The aim of the present study was to identify metabolites responsible for the antimicrobial and disease-suppressive activities of this isolate. Fermentation broth of LEC was fractionated by preparative HPLC and the resulting single fractions were analyzed by HPLC-ESI-MS. In vitro growth suppression by single fractions was apparent in agar diffusion and microtiter plate assays for Fusarium culmorum , Pythium ultimum , and Bacillus megaterium , but not for Escherichia coli . For F. culmorum and Py. ultimum , suppression was caused by fractions containing precursor ions m/z 511.28 ( z = 1) and m/z 513.30 ( z = 1), that are characteristic for members of the group of polycyclic tetramate macrolactams (PoTeMs) like alteramides, heat stable antifungal factor (HSAF) and derivatives thereof. The inhibition of B. megaterium was caused by a much broader spectrum of fractions that also contained different precursor ions. In vitro tests with Phytophthora infestans and climate chamber tests with Pseudoperonospora cubensis on cucumber plants were carried out with pooled groups from the single fractions. Significant and dose-dependent activity was exclusively observed for the pooled group containing PoTeMs, which was in agreement with the results of the plate assays. Activity comparable to a copper-containing fungicide was apparent in a concentration that corresponded to 3% or higher of the original fermentation broth. We therefore assume that PoTeMs are responsible for the biocontrol activity of isolate LEC. These findings confirm the capability and suitability of LEC as a biocontrol agent.