16S rRNA of Fox: feces
The 16S rRNA amplicon sequencing was conducted using Illumina MiSeq Next-Gen Sequencer under previously optimised settings. To process the v3-v4 regions of the bacterial 16S rRNA gene, the forward primer GCCTACGGGNGGCWGCAG and the reverse primer GGACTACHVGGGTATCTAATCC were used (Sargent, 2020). Following that, FIGARO v1.1.2 (Weinstein et al., 2019) and fastp v0.23.4 (Chen, 2023; Chen et al., 2018) were  used to determine optimal trimming parameters. Then, Quantitative Insights Into Microbial Ecology 2 (QIIME2) was used to conduct the metagenomic analyses using the following procedure(Bolyen et al., 2019). Firstly, the paired end sequences were imported and merged. This was followed by demultiplexing the paired-end sequence reads, and further generating a summary of the sequence quality information. Based on the information of sequence quality, Divisive Amplicon Denoising Algorithm (DADA2; Callahan et al., 2016) was then used to denoise the paired-end sequence reads. The paired-end sequences that contain low quality regions (i.e., sequence quality score <30) were removed.