2.3.1. Sequence screening and preparations for meta-analysis
We used Quantitative Insights into Microbial Ecology (QIIME2) version 2019.10 [18], for the meta-analysis. QIIME2 pipeline provides a start-to-finish workflow, beginning with demultiplexing sequence reads and finishing with taxonomic and phylogenetic profiles. The sequences from the individual study were imported to QIIME2 using CasavaOneEight format, and the quality of the sequences was checked by the default settings in QIIME2. Based on the sequence quality, the sequence was trimmed, denoised, aligned and checked for chimera using DADA2 (single and paired-ends sequence were trimmed based on the length of primer used) [21]. The feature table and representative sequence of each file were merged using QIIME2 feature merge table and merged representative sequences.