Maximum parsimony tree of arsB Permease sequences. The optimal tree with the sum of branch lengths = 2.73 is shown. 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 evolutionary distances are in the units of the number of base substitutions per site. All sequenced codon positions were included in the alignment, for introns and exons in arsB; however, every site containing gaps or missing data was then eliminated from the dataset. There were a total of 707 positions in the final dataset. arsB genes from different bacteria were used as indicated in the tree by their name, followed by the GenBank accession numbers. The consensus sequences of Q18 and Q63 samples were used to construct the tree.