Figure 12

A plausible evolutionary pathway of the PAH-degrading mycobacterial group. The scheme is based on the gene gain and loss of PAH-degrading genes and the genomic information (genome and pan-genomes). The size of circles indicates the ratio of the relative size of the genomes. The complete black circles indicate a mycobacterium with the complete gene set for PAH-degradation, while partially blacked circles indicate PAH-non-degrading mycobacteria with incomplete PAH-degrading genes. More filled circles mean more PAH-degrading genes in the genome. Color shading follows Figure 11. Note that all PAH-degrading mycobacteria have larger genome size and more HGT events than PAH-non-degrading mycobacteria, which have some PAH-degrading genes but not a complete set of genes. Especially, OI mycobacteria have the smallest size in terms of genome and the number of PAH-degrading genes. Under strong natural selection, the gene gain/loss by HGT/deletion events hypothesize an epistasis-based birth (from CAP to RCP via SCP) and pleiotropy-dependent death (from RCP and CAP to SCP), for PAH metabolism in the genus Mycobacterium.