Figure 4

Taxonomic distribution of sequences from prokaryotes. (a) On the basis of its phylogenetic profile, each sequence is assigned to a single evolutionary group within their domain. A schematic detailing the phylogenetic relationships of the defined prokaryotic groups is provided in the lower left of the figure. For each taxonomic group the numbers represent: number of genomes analyzed (white text on black); percentage of sequences that are species-specific (black text on white); percentage of sequences that are taxon specific - that is, share sequence similarity only with a sequence(s) from a species from the same taxon (light gray background); and the total number of sequences. Numbers in dark gray boxes indicate the percentage of sequences with similarity to sequence(s) from the neighboring taxon, but not to any other taxon, and may thus represent lineage specific sequences. The numbers in the blue triangle represents the percentage of sequences from each of the three major groups of proteobacteria (alpha, beta and gamma/delta/epsilon) with sequence similarity to each of the other proteobacterial groups). The numbers in the middle of the triangle indicate the percentage of genes from each group (alpha, beta and gamma/delta/epsilon top to bottom) that have sequence similarity to both of the other two groups. (b) Bar chart showing the distribution of sequences with sequence similarity to sequences from other bacterial groups, ordered by frequency. Each bar is colored by the groups represented; for example, the first bar from the left indicates the number of sequences from spirochaetes, cyanobacteria and 'other bacterial groups' that have significant sequence similarity to a sequence in each of the other two groups. The largest group, on the right, consists of 145,647 sequences that have similarity to all six prokaryotic groups.