In agreement with previous observations of expansions of molybdopterin biosynthesis genes, we observe five protein domains related to pterin cofactor biosynthesis among the top protein domains expanded in the Mtb complex compared to the non-pathogenic Mycobacteria ( Table 2 , -"d"). Among the top GO terms expanded in the Mtb clade relative to the soil dwellers (Table 3) , there are also several groups involved in pterin and molybdopterin biosynthesis. Some of these gene copies (the moa1 locus) are believed to have been acquired by lateral gene transfer on the branch leading to the Mtb complex [10, 50] .