Phylogenetic distribution of RelE toxin sequences. Amino acid sequences homologous to the pTRACA22 RelE (ORF22-6, Figure 1, Table S1) derived from combined human gut metagenomes, plasmids and bacterial genome sequences, were used for construction of a phylogenetic trees. Symbols preceding sequence names denote the origin of the RelE sequence as detailed in the figure legend. Major clades predominantly populated with sequences of common phylogenetic origin are indicated by brackets: A) Firmicutes B) Bacteroidetes/Chlorobi, C) Plasmid D) Proteobacteria E) Actinobacteria. Numerals indicate nodes with bootstrap values of 40 or over (based on 1000 replicates). Scale bar indicates 0.1 amino acid substitutions per site. Accession numbers for chromosomal and plasmid sequences represented in the phylogenetic tree, along with those for gut metagenomic sequences encoding each RelE "type" are listed in Table S2.