Symbioses: Plant, Animal, and Microbe Interactions
Hoffman, Michele T. , Arnold, A.E. .
Fungal endophytes harbor diverse, horizontally transmitted bacterial endosymbionts that can alter the fungal phenotype in vitro .
Here, we report that phylogenetically diverse bacterial endosymbionts occur within living hyphae of multiple major lineages of ascomycetous endophytes. Four hundred and fourteen isolates of endophytic Pezizomycotina, isolated from six species of cupressaceous trees in five biogeographic provinces, were evaluated for the presence of bacterial endosymbionts using a combination of microscopy and molecular techniques. Viable bacteria were observed within living hyphae of Pezizomycetes, Dothideomycetes, Eurotiomycetes, and Sordariomycetes. Most endohyphal bacteria were Proteobacteria, with eight families represented. None of the genotypes matched known bacterial associates of plants, hinting at a distinctive endosymbiotic niche within fungal hyphae. Loss of bacterial endosymbionts following subculturing in a large proportion of isolates suggested a facultative association. A focus on 28 fungal/bacterial associations revealed that bacterial and fungal phylogenies are incongruent with each other and did not reflect the phylogenetic relationships of host plants. Instead, both endophyte and bacterial assemblages were strongly structured by geography, consistent with local horizontal transmission. Endophytes could be cured of their bacterial endosymbionts using antibiotics, providing a tractable experimental system. Studies of seven focal fungal/bacterial pairs showed that bacteria could significantly alter growth of fungi at different nutrient, pH, and temperature levels in vitro, and that different members of the same bacterial lineages interact with different fungi in different ways. The potential for such interactions to shape endophyte/host associations will be discussed.
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1 - University of Arizona, Department of Plant Sciences, Division of Plant Pathology and Microbiology, 1140 E. South Campus Drive, Forbes 303, Tucson, AZ, 85721, USA
2 - The University of Arizona, Department of Plant Sciences, Division of Plant Pathology and Microbiology, 1140 E. South Campus Drive, Forbes 303, Tucson, AZ, 85721, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Wasatch B/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 8:30 AM