The V4 region of the 16S rRNA gene was amplified using Earth Microbiome Project primers 515F (5-GTGYCAGCMGCCGCGGTAA-3) and 806R (5-GGACTACNVGGGTWTCTAAT-3). PCR was performed for 30 cycles using Phusion High-Fidelity PCR Master Mix. Approximately 300-bp amplicons were verified by agarose gel electrophoresis. Indexed sequencing libraries were prepared using the Illumina TruSeq DNA PCR-Free Sample Preparation Kit and evaluated using a Qubit 2.0 Fluorometer and Agilent Bioanalyzer 2100 before sequencing.