Unless otherwise stated, UCHIME results were obtained using the USEARCH v4.2.52. Perseus results were obtained using v1.24 of the AmpliconNoise package. MAFFT v6.853 (Katoh and Toh, 2008 (link)) was used by Perseus to create alignments. The reference database used for both ChimeraSlayer and UCHIME was the ‘gold’ set in http://sourceforge.net/projects/microbiomeutil/files/, version 2011-11-02. Unless otherwise stated, Perseus results were obtained using PerseusD v1.24, a variant of the original Perseus algorithm that follows UCHIME by only testing parents that have been classified as non-chimeric and are at least twice as abundant as the query. For a comparison of Perseus with PerseusD, see the Supplemental Material.