Paraburkholderia fungorum GIB024 specifically promotes the mycelial growth of ectomycorrhizal fungi

Abstract Ectomycorrhiza (ECM) sporocarp harbors unique bacteria with high mutual specificity toward their fungal host. However, a high versatile and wide pervasive bacterium, Paraburkholderia fungorum strain GIB024, has been isolated from a Rhizopogon roseolus sporocarp in a Pinus thunbergii forest. Therefore, the specificity interaction pattern toward ECM fungi by the bacterium became intriguing. In vitro agar-based plate approaches of confrontation assays as well as application of a sterilized bacterial suspension to various ECM fungal genera regarding growth promotion were employed. The bacterium significantly promoted the growth of Suillus bovinus, but not R. roseolus, in low sugar medium. However, the opposite result was obtained in the high sugar medium. We then extended the bioassay in low sugar medium to focus on Suillus spp. in association with various plant hosts. GIB024 significantly promoted S. bovinus growth in association with P. thunbergii, but not with P. densiflora. The bacterium had a neutral or inhibitory effect on the growth of other Suillus spp. associated with P. thunbergii as well as other Pinaceae. Furthermore, application of a sterilized bacterial suspension produced effects resembling those of the confrontation assay. These results emphasized the significant role of plant host on determining the mycelial growth-promoting specificity of ECM-associated bacteria.