Fig. 2: Principal component analysis (PCA) of species-level microbial composition across 139 metagenomic samples.

Biplot showing the ordination of metagenomic samples based on centered log ratio-transformed (CLR) species-level abundance data. PCA was performed to explore variation in microbial community structure across sample sources and countries. Each point represents an individual sample, colored by source type. Arrows represent the top 10 species contributing most to the ordination space, with arrow direction indicating the gradient of increasing abundance and arrow length corresponding to the strength of contribution to the principal components.