Discovery of novel microorganisms and antimicrobial traits in natural disease suppressive soils

PO-50 discovery of novel microorganisms and antimicrobial traits in natural disease suppressive soils Menno van der Voort1, Rodrigo Mendes1, Marco Kruijt1, Irene de Bruijn1, Ester Dekkers1, Peter A H M Bakker2, Yvette M Piceno3, Todd Z DeSantis3, Gary L Andersen3, Jos M Raaijmakers1 1Laboratory of Phytopathology, Wageningen University, Wageningen, The Netherlands, 2Plant-Microbe Interactions, Department of Biology, Utrecht University, Utrecht, The Netherlands; 3Ecology Department, Lawrence Berkeley National Lab, Berkeley, CA, USA. Soil ecosystems represent an enormous untapped resource for discovering novel microorganisms, traits and bioactive genes. Specific soils have been identified worldwide in which beneficial microorganisms guard plants against soil-borne pathogen infections. However, the microbiological and molecular mechanisms underlying this soil immune response are largely unknown. In the present work, the microorganisms and mechanisms involved in natural suppressiveness of soils to the fungal pathogen Rhizoctonia solani were investigated by culture-dependent and independent approaches. Culture-dependent analyses revealed quantitative and qualitative differences in bacterial populations between Rhizoctonia suppressive and conducive soils. The culture-independent PhyloChip analyses identified the bacterial communities from soils with different levels of disease suppressiveness and specifically pointed to the Proteobacteria as an important phylum and dynamic group associated with disease suppression. Although the richness of strains was not significantly different between suppressive and conducive soils, the relative abundance of specific groups correlated well with the different levels of soil suppressiveness. Subsequent genotyping and functional analyses led to the identification of novel Pseudomonas species with activity against Rhizoctonia solani. This activity was found to be due to a novel chlorinated peptide encoded by a large nonribosomal peptide synthetase gene cluster. In conclusion, this study provides new insights into the microbial diversity and fundamental mechanisms underlying multitrophic interactions in natural disease suppressive soils.