design: We amplified the V4 hypervariable region of 16S rRNA gene using dual-indexed primers (515f / 806) as described by Kozich et al. (2013). Pooled amplicon libraries were submitted for sequencing at the Cornell Core Facility in Ithaca, NY. Samples were run on an Illumina MiSeq using V2 chemistry with 2 x 250 bp read length.