The Role of Reticulate Evolution in Creating Innovation and Complexity

Figure 2

Distribution of the two gene clusters involved in vitamin B₁₂ biosynthesis among the Thermotogae phylum. The corrinoid synthesis gene cluster contains genes for the first part of the de novo B₁₂ synthesis pathway and the cobinamide salvage gene cluster contains genes that synthesize vitamin B₁₂ from cobinamides, incomplete B₁₂ molecules. Together these two gene clusters complete the de novo B₁₂ biosynthesis pathway. Presence of a gene cluster is denoted by (+) and absence is denoted by (−). The most parsimonious explanation for the extant presence/absence patterning for the cobinamide salvage gene cluster is one gain at the root of the phylum and three losses marked by blue and (+) and (−) and for the corrinoid synthesis gene cluster one gain marked by a red (+). This suggests the cobinamide salvage pathway was present in the ancestor of the Thermotogae phylum and the genes for complete de novo synthesis were gained in a later event by the Thermosipho lineage.