The Wheat Head Blight Pathogen Can Recruit Collaborating Bacteria from Soil.

In nature, fungal endophytes often have facultative endohyphal bacteria (FEB). Can a model plant pathogenic fungus have them, and does it affect their phenotype? We constructed a growth system/microcosm to allow an isolate to grow through natural soil and then re-isolated it on a gentamicin-containing medium, allowing endohyphal growth of bacteria while killing other bacteria. PH-1 labelled with a gene staining the fungal nuclei fluorescent red was used to confirm the re-isolation of the fungus. Most new re-isolates contained about 10 genes per fungal gene determined by qPCR. The + FEB holobiont isolates containing the bacteria were sub-cultured several times, and their bacterial contents were stable. Sequencing the bacterial gene from several Fg-FEB holobiont isolates revealed endophytic bacteria known to be capable of nitrogen fixation. We tested the pathogenicity of one common Fg-FEB holobiont association, + , and found increased pathogenicity. The gene load per fungal gene inside the wheat stayed the same as previously found in vitro. Finally, strong evidence was found for Fg- symbiotic nitrogen fixation benefitting the fungus.