Protein maximum likelihood trees of A-type flavoprotein ( fprA gene). ML trees based 269 unambiguously aligned aa positions of the A-type flavoprotein. The boxes indicate sequences that have an approximately 450 aa long conserved C-terminal extension of the flavoprotein which is absent from all other sequences in the alignment (see Additional File 4 for further analyses and discussion). The grey boxes A and B indicate strongly separated groups which include eukaryotic sequences. The tree is arbitrarily rooted. Details about the phylogenetic analyses are found in the Methods section and Additional File 2. Labelling as in Figure 2.