design: A total amount of 1 g of metagenomic DNA per sample was used as input material for the DNA sample preparations. Sequencing libraries were generated using NEBNext Ultra DNA Library Prep Kit for Illumina (New England Biolab, Ipswich, MA, USA) following the manufacturers recommendations and index codes were added to attribute sequences to each sample. Briefly, the DNA sample was fragmented by sonication to a size of 300 bp, then DNA fragments were end-polished, A-tailed, and ligated with the full-length adaptor for Illumina sequencing with further PCR amplification. The PCR products were purified (AMPure XP system) and libraries were analysed for size distribution by the Agilent 2100 Bioanalyzer and quantified using real-time PCR. Clustering of index-coded samples was performed on a cBot Cluster Generation System according to the manufacturers instructions. After cluster generation, the library preparations were sequenced on an Illumina NovaSeq 6000 platform and 150-bp paired-end reads were generated.