enrichment
MiSeq sequencing was performed using 515F (Turner et al., 1999) and 928R (Wang and Qian, 2009) primers for amplification of 16S rRNA gene. Single multiplexing was performed using home made 6 bp index, which were added to reverse primer during a second PCR with 12 cycles using forward primer and reverse primer. The resulting PCR products were purified and loaded onto the Illumina MiSeq cartridge according to the manufacturer instructions. The quality of the run was checked internally using PhiX, and then each pair-end sequences were assigned to its sample with the help of the previously integrated index.