sequencing of metagenome
The sediments scratched from the filter membranes were digested with Proteinase K and RNase A, and genomic DNA fragments were extracted with magnetic beads. A biomass of 1 g genomic DNA was fragmented and fragments with lengths varied from 200 bp to 400 bp were selected for end-repaired, 3 adenylation and ligation to adaptors. The resulted fragments were used for product amplification and circularization, and the uncyclized linear DNA molecules were digested.