Real-Time PCR assays were carried out in order to quantify the total bacterial 16S rRNA and key functional genes for methanogenesis (mcrA), sulfate reduction (dsrA) and nitrate reduction (nirK and nirS) using primers: 338f/518r, Met1f/Met1r, dsr-1F 50/dsr-500r 50, nirK876/nirK1040 and nirSCd3aF/nirSR3cd, respectively (SI Table S2).