design: Microbial DNA was extracted from fecal and proximal colon samples (~100 mg) using the Quick-DNA Fecal/Soil Microbe Kit (Zymo Research). The V4 region of the 16S rRNA gene was amplified using primers 515F/806R, with an 8 bp barcode and Illumina adapter. PCR amplification was performed in triplicate, and negative controls were included to assess contamination. The pooled and purified DNA library was sequenced on the Illumina MiSeq platform (250 bp paired-end) at the University of California Davis Genome Center.