Predicted time ranges of horizontal transfer events. Evolutionary time ranges symbolized by horizontal lines are shown during which horizontal gene transfer events may have occurred to explain the phylogenetic trees provided in Additional file10. Each line is associated with a set of proteins reported by Zhaxybayeva et al. to contain at least one conflict with the 16 S rRNA gene tree. The termini of the time ranges are defined by evolutionary events deduced from the 16 S rRNA gene tree (Figure 1), either the divergence of a single organism (represented by the symbol of that organism) from many or the divergence of one or two organisms from one or two other organisms (represented by the diverging organisms symbols separated by a slash). Evolutionary time proceeds left to right, roughly proportional to the number of mutations that have accumulated in ribosomal DNA. The scores of the gene or genes (averaged) predicted to have resulted from horizontal gene transfer are given at the right, according to the four methods considered. Green lines indicate time periods that are at least partially as recent as the divergence of Pmf/Pmt from Synechococcus.