design: A subset of samples was selected for 18S rRNA gene amplicon sequencing based on metagenomic contig classification, targeting samples with more than 5% non-bacterial contigs. The 18S rRNA gene was amplified using primers 566F/1289R, barcoded using the Oxford Nanopore Native Barcoding Kit, and sequenced on a GridION Mk1 platform using R10.4 flow cells with high-accuracy basecalling.