design: PCR primers targeting Bacteria and Archaea were used for amplification of the V4 region of 16S rRNA genes with dual barcoded forward primer 515F and reverse primer 806R (Kozich et al. 2013; 10.1128/AEM.01043-13). The forward primer was linked to Illumina adapter as follows: 5' Illumina adapter - 8 bp barcode - Forward primer pad - 2 bp linker - Forward primer, 515F (515F: AATGATACGGCGACCACCGAGATCTACAC NNNNNNNN TATGGTAATT GT GTGCCAGCMGCCGCGGTAA). The reverse primer was linked to Illumina adapter as follows: Reverse complement of 3' Illumina adapter - 8 bp barcode - Reverse primer pad - 2 bp linker - Reverse primer, 806R (806R: CAAGCAGAAGACGGCATACGAGAT NNNNNNNN AGTCAGTCAG CC GGACTACHVGGGTWTCTAAT)