Isolation and morphological and metabolic characterization of common endophytes in annually burned tallgrass prairie

Abstract

Dark septate endophytes (DSE) are common and abundant root-colonizing fungi in the native tallgrass prairie. To characterize DSE fungi were isolated from roots of mixed tallgrass prairie plant communities. Isolates were grouped according to morphology, and the grouping was refined by ITS-RFLP and/or sequencing of the ITS region. Sporulating species of Periconia, Fusarium, Microdochium and Aspergillus were isolated along with many sterile fungi. Leek resynthesis was used to quickly screen for DSE fungi among the isolates. Periconia macro-spinosa and Microdochium sp. formed typical DSE structures in the roots; Periconia produced melanized intracellular microsclerotia in host root cortex, whereas Microdochium produced abundant melanized inter- and intracellular chlamydospores. To further validate the results of the leek resynthesis growth responses of leek and a dominant prairie grass, Andropogon gerardii, were assessed in a laboratory resynthesis system. Leek growth mainly was unresponsive to the inoculation with Periconia or Microdochium, whereas Andropogon tended to respond positively. Select Periconia and Microdochium isolates were tested further for their enzymatic capabilities and for ability to use organic and inorganic nitrogen sources. These fungi tested positive for amylase, cellulase, polyphenol oxidases and gelatinase. Periconia isolates used both organic and inorganic nitrogen sources. Our study identified distinct endophytes in a tallgrass prairie ecosystem and indicated that these endo-phytes can use a variety of complex nutrient sources, suggesting facultative biotrophic and saprotrophic habits.

Arabidopsis thaliana model system reveals a continuum of responses to root endophyte colonization

“…Microsclerotia and melanized hyphae were recorded in Periconia treatments, and chlamydospores in the Microdochium treatments, as was expected for these two endophytes (Mandyam et al 2010). The fungus-free controls remained free of colonization confirming absence of contamination.…”

“…isolates were used for the laboratory inoculation assays. These fungi originated from KPBS, were identified based on colony and conidial morphology plus Internal Transcribed Spacer sequencing, and ultimately confirmed to be root-associated endophytes according to Koch's postulates (Mandyam et al 2010). While some isolated aspergilli and fusaria in Mandyam et al (2010) were clearly pathogenic and led to plant mortality, inoculation with the Periconia and Microdochium isolates did not result in disease symptoms and were therefore selected for further studies.…”

“…This site was selected because it is also the source of isolates used in resynthesis studies and has been shown to have high occurrence of endophytes in native plants , Mandyam et al 2010). Rocks and large roots were removed and the field soil was thoroughly mixed with an equal volume of autoclaved Promix general purpose growing medium (Premier Horticulture, Quakertown, Pennsylvania, USA).…”

“…We argue that the access to tools available for model plants far outweigh the disadvantages of remote ecological relevance in many natural systems. Our goal is to strive towards an improved understanding of the influence of host and fungal genotypes on the outcome of the DSE symbiosis along the mutualism-parasitism continuum by using three selfed accessions of A. thaliana and several strains of abundant DSE fungi from a native tallgrass prairie (Mandyam, Loughlin & Jumpponen 2010). Our specific goals were to evaluate i) microscopically Arabidopsis colonization by the DSE fungi under field, greenhouse, and laboratory conditions; ii) Arabidopsis responses to a range of DSE isolates distributed across two taxa that commonly occur in a tallgrass prairie ecosystem; and iii) whether host responses vary across genotypes of conspecific fungi and/or host accessions or combinations thereof.…”

Effect of different root endophytic fungi on plant community structure in experimental microcosms

“…Such chlamydospores are not produced by any other of the isolates used, and it is very unlikely that contaminants could produce such features. Moreover, this type of chlamydospore has been frequently reported during colonization of endophytic Microdochium strains in temperate grasses (Mandyam et al., 2010). Further, we did not identify any AMF structures in the roots, indicating that these fungi were absent from the soil and did not drive any of the plant growth effects.…”