Digester 2 surface
Total DNA extractions were performed in triplicate using PowerSoil DNA Isolation kit (MO BIO) following the manufacturer instructions. The DNA was stored at -20C until use. The V4V5 hypervariable region of the 16S rRNA gene targeting Bacteria and Archaea was amplified using the primers 515F, 5  GTG YCA GCM GCC GCG GTA  3 and 928R, 5  CCC CGY CAA TTC MTT TRA GT  3 (Anderson et al., 2009; Liu and Whitman, 2008). The amplifications of the 16S rRNA gene were performed in a final volume of 50 L with primers 515F/928R (0.2 M), 0.2 mM dNTPs, 1.25U Taq polymerase (Amp Taq Gold 360) and its buffer. The amplification reactions are carried out according to the following program: 1 cycle of 10 min at 94 C (denaturation); 35 cycles of 3 steps: denaturation at 94 C, hybridization at 65 C, and elongation 40 sec at 72 C; final elongation cycle of 10 minutes at 72 C. Amplification was conducted using a PCR thermal cycler Model PTC-100 (Bio-Rad, Richmond, CA). Forwards and reverse primers contained the adapter sequences (5GTGYCAGCMGCCGCGGTA) and (3ACTYAAAKGAATTGRCGGGG) respectively, used in Illumina sequencing technology. The amplicons were sequenced using an Illumina MiSeq (250 bp paired-end reads) at the platform Genotoul Inc. (www.genotoul.fr, Toulouse, France).