design: Total genomic DNA was extracted from each biofilm sample using a TIANamp Soil DNA Kit (TIANGEN BIOTECH, BeiJing, China) according to the manufacturers instructions. The concentration and purity of the extracted DNA were determined using Qubit4 (Thermo Fisher Scientific, Illinois, U.S.). A protocol modified from one previously described (Rinke et al. 2016) was used for the construction of the paired-end sequencing library. Briefly, less than 1 ng (0.1 ng/ul-1 ng/ul) of extracted DNA from biofilm samples was fragmented by a transposase reaction mix (5 l of 2 TD buffer, 2.5 l of transposase (BioGenuineTech, Shanghai, China), and 1.5 l of nuclease-free water) for 10 mins at 55 C. Then, the tagmentation mixture was amplified for 12-18 cycles by Phusion with an MGI adapter using a DNA library kit (BioGenuineTech, ShangHai, China) and sequenced using DNBSEQ-T7 (MGI) with PE150 for 6G.