Fig. 4.

Schematic diagram depicting the potential community-dependent evolutionary model of Acidithiobacillus population. Extremely acidic environments as potential physical barrier might contribute to geographical isolation. Varied gene flow occurs in isolated microbial communities of ecological niches around the world. Gene gain events via various horizontal gene transfer expand the gene repertoires of bacterial genomes, and gain loss events dependent on microbial community increase cellular economization, thereby resulting in the allopatric speciation.