Figure 2.

Lateral gene transfer in the evolution of ABR genes. Bars next to the operational taxonomic units show the frequency of redundant amino acid sequences (with highest frequency noted). (a) The outer ring shows the genus of ABR gene origin; the inner ring shows whether the gene is encoded on a plasmid (Pls) or chromosome (Chr). (b,c) Isolate label is coloured according to replicon type (plasmid genes in pink and chromosomal genes in blue). Most phylogenetic trees we reconstructed here for the ABR genes included polytomies, hence donor and recipients in the gene transfer events cannot be reliably inferred. Nonetheless, considering the presence of the examined ABR genes on both plasmids and chromosomes supports the hypothesis that they have been transferred at least once in their evolutionary history.