Supplementary Methods

<b>Supplementary Table 1</b> The amount and percentage of contaminant sequences in the negative control that passed through quality filtering and clustered into operational taxonomic units (OTUs). The negative control contained trace contaminants from nine of the 16 mock community members. This is presumably due to cross-contamination during PCR and library preparation steps, despite surface sterilization and stringency in protocols. <b>Supplementary Table 2</b> Amount of Operational Taxonomic Units (OTUs) before and after filtering. For the mock libraries (A, B, and C). OTUs that were chimeric were removed, and OTUs that matched ≤95% to one of the mock community members were considered to be a weak consensus match and were also removed.