Sludge
DNA was extracted from the 0.5 g of sludge sample by using the Fast-DNA SPIN kit for soil (MP Biomedicals, USA) following the manufacturers instructions. PCR amplifications of arrA, arsC, dsrA, dsrB and 16S rRNA genes were performed with the primers As1F/As1R (Zhang et al., 2015), amlt-42-F/amlt-376-R (Sun et al., 2014), Dsr1F+/Dsr-R (Kondo et al., 2014), DSRp2060F/DSR4R (Geets et al., 2006) and 1369F/1492R (Suzuki et al., 2000), respectively. Purified amplicons were pooled in equimolar and paired-end sequenced on an Illumina MiSeq PE300 platform/NovaSeq PE250 platform (Illumina, San Diego,USA) according to the standard protocols by Majorbio Bio-Pharm Technology Co. Ltd. (Shanghai, China).