Fig. 2

Evolutionary relationships of representative IS1447_like OrfAB protein sequences. The evolutionary history was inferred using the Neighbor-Joining method [60]. The optimal tree with the sum of branch length = 13.53466248 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches [38]. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The bar indicates 0.1 estimated changes per amino acid. Most of the sequences from non-Firmicutes species are clustered into one branch as shown in Additional file 1: Figure S1, which is compressed as a black triangle in this figure. The sequence from C. thermocellum DSM1313 (also named as Ruminiclostridium thermocellum DSM1313 or Hungateiclostridium thermocellum DSM1313) is in bold. Non-Firmicutes sequences that are clustered into the Firmicutes branch and their phylum-level affinitions are shown with color. The class-level affinitions of the sequences are shown in gray boxes to the right of the Figure. The accession numbers of the nucleotide sequences are given in front of the species names. The strains with OrfAB proteins that are translated via no or − 1 slippage are marked by the asterisk or pound sign, respectively. The nucleotide and amino acid sequences of the IS1447-like genes that perform + 1 transcriptional slippage are listed in Additional file 2: Table S3