Emergence of Antagonism Against the Pathogenic Fungus Fusarium oxysporum by Interplay Among Non-Antagonistic Bacteria in a Hydroponics Using Multiple Parallel Mineralization

The rhizosphere microbial community in a multiple parallel mineralization (MPM) system contributes to suppression of root-borne diseases. We hypothesized this phenomenon can be attributed to the interplay of non-antagonistic bacteria rather than to a single antagonistic microbe. In this study, we tested this hypothesis by investigating the potential roles of bacterial interplay in a subset of MPM microbiota in the suppression of the fungal phytopathogen Fusarium oxysporum. Bacterial strains isolated from the MPM system were subjected to in vitro and in planta tests on F. oxysporum. A community of seven bacterial strains (Kaistia sp. TBD58, Sphingopyxis sp. TBD84, Bosea sp. TBD101, Ancylobacter sp. TBD132, Cupriavidus sp. TBD162, Brevibacillus sp. TBD179 and Sphingopyxis sp. TBD181) suppressed F. oxysporum growth. None of the strains alone was antagonistic against F. oxysporum, whereas several pairs of those non-antagonistic strains inhibited its growth. Morphological observations showed the formation of swollen F. oxysporum cells in the presence of these bacterial pairs. The same bacterial pairs also suppressed Fusarium wilt disease in Arabidopsis thaliana. These results indicate that a complex bacterial interplay among non-antagonistic bacteria can significantly contribute to the development of antagonism against F. oxysporum in the context of the MPM system.