design: Briefly, the DNA of frozen (-80C) samples was extracted using the DNeasy Power Soil Kit (Qiagen, Venlo, The Netherlands). After quality controls of the extracted DNA, the V3-V4 variable regions of the 16S rRNA gene were amplified in a one-step PCR (30x cycles: 98 C/30 s - 98 C/9 s - 55 C/1 min - 72 C/1.30 min - 72 C/10 min - hold at 4C) using the primer pair 341F-806R. After verification of the presence of PCR-products by gel electrophoresis, normalisation (SequalPrep Normalisation Plate Kit; ThermoFisher Scientific, Waltham, USA) and equimolar pooling was performed. Sequencing was conducted on the MiSeq platform (MiSeqFGx; Illumina, San Diego, USA) with v3 chemistry.