Low-diversity but phylogenetically broad mock communities were created as follows. Amanita muscaria 3-1-B2-1-2s (Basidiomycota, isolated from Alaskan fruitbody), Amphinema byssoides R-NC03 (Basidiomycota, isolated from Picea abies ectomycorrhiza in Finland), Coprinopsis cinereus (Basidiomycota, obtained from the Fungal Genetics Stock Center, strain FGSC 9003), Mortierella alpina (Mucoromycotina, obtained from the American Type Culture Collection, strain 42430), Spizellomyces punctatus (Chytridiomycota, obtained from the American Type Culture Collection, strain 48900), Tricholoma vaccinum 18-1-B1-A1-2s (Basidiomycota, isolated from Alaskan fruitbody), and Tylospora asterophora R-MF02 (Basidiomycota, isolated from Picea abies ectomycorrhiza in Finland) were grown in modified Melin-Norkrans (MMN) broth for up to 6 months on a rotary shaker at room temperature. Mycelium was harvested by filtration through cheesecloth, freeze-dried, and then ground in liquid nitrogen with a mortar and pestle. Genomic DNAs were isolated using the Qiagen Genomic-tip kit. Genomic DNA from Schizosaccharomyces pombe strain 972 h- was provided by the Broad Institute. Genomic DNA concentrations were estimated by fluorescence on a NanoDrop 3300 using PicoGreen (Quant-iT kit; Invitrogen) with lambda DNA standards. The averages of three NanoDrop 3300 readings were used for calculations. The 5.8S-Fun/ITS4-Fun amplicons (including core primers but not adaptors) for these eight taxa range from 396 to 514 bp (mean, 440 bp). Two “tiered” mock communities were created wherein taxa were randomly assigned to high, medium-high, medium-low, and low relative abundances (see Table S1 in the supplemental material). These abundances spanned three orders of magnitude (0.043% to 43%). Different taxa were assigned to the 4 abundance levels in the two communities, designated mock A and mock B. Both mock communities had final concentrations of 11.2 ng/μl.
In order to evaluate the performance of our primers on a more complex real-world fungal community, we also analyzed five soil DNA extracts that have been extensively analyzed using large-scale Sanger sequencing of ITS-LSU clone libraries (4 (link), 53 (link)). These boreal forest soil DNAs were extracted using the Mo Bio PowerMax kit (Mo Bio Laboratories, Carlsbad, CA, USA) and normalized to 2.5 ng/μl. The TKN sample is from a lowland black spruce (Picea mariana ) forest, UP1 samples are from early stage upland mixed forest, and UP3 samples are from a late-stage upland white spruce (Picea glauca ) forest. Samples with an “O” are from the organic horizon, while samples labeled “M” are from the mineral horizon. The final number indicates the collection year, e.g., 2004. Detailed descriptions of these sites and samples are in references 4 (link), 53 (link), and 54 (link).
In order to evaluate the performance of our primers on a more complex real-world fungal community, we also analyzed five soil DNA extracts that have been extensively analyzed using large-scale Sanger sequencing of ITS-LSU clone libraries (4 (link), 53 (link)). These boreal forest soil DNAs were extracted using the Mo Bio PowerMax kit (Mo Bio Laboratories, Carlsbad, CA, USA) and normalized to 2.5 ng/μl. The TKN sample is from a lowland black spruce (
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