Statistical analysis. Barcoded amplicon libraries of the small subunit ribosomal RNA gene V4 hyper variable region will be generated for each of the sample using V4 forward primer GTGCCAGCMGCCGCGGTAA and V4 reverse primer GGACTACHVGGGTWTCTAAT as described by Schloss in http://www.mothur.org/wiki/File:Wet-lab_MiSeq_SOP.pdf. The amplicon libraries will be pooled in equimolar amounts and sequenced by means of Illumina MiSeq system. The sequencing data will be processed using a combination of QIIME (15) and UPARSE (16) pipelines. After quality filtering, the reads will be clustered into Operational Taxonomic Units (OTUs) at a minimal sequence similarity of 97% using UPARSE. The representative sequence of each cluster will be assigned a taxonomy using the Ribosomal Database Project (RDP) classifier with 80% confidence in QIIME.