Fig. 1.

Maximum likelihood phylogenetic tree of the 16S rRNA sequences of our 22 isolates showing positive aoxB PCR amplification. This tree also includes 16S rRNA sequences deposited in public databases, corresponding to the organisms found (or close relatives) to carry the aoxB gene or closely related organisms. The tree was rooted in between Archaea and Bacteria domains. Phylogenetic analyses were performed on the 1,014 unambiguously aligned nucleic acid positions by using Treefinder (19). The evolutionary model GTR + Γ4 was used for this purpose, as suggested by the “propose model” tool available in Treefinder. Numbers at branches are bootstrap values obtained using the nonparametric bootstrap approach implemented in Treefinder (based on 100 replicates of the original data set). Only bootstrap values above 50% are shown. Bacteria harboring aoxB sequences corresponding to phylogenetic group I or group II or neither of these two groups are given in pink, dark blue, or green, respectively. The 22 bacterial isolates of this study are in boldface and underlined. All bacteria experimentally shown to be able to oxidize arsenite are labeled with a circle at the end of the name. Bacteria which were previously shown to be able to oxidize arsenite or harbor an aoxB gene, but for which no 16S sequence was available, were therefore not included in this tree. However, in this case, we included the closest relative of these strains for which a 16S gene was available (in gray), and the triangle color at the end of these names corresponds to the group to which the aoxB gene harbored by the strain belongs (pink, dark blue, and green corresponding to group I, group II, and neither of these groups, respectively). The names of bacteria which were described in the literature as able to oxidize arsenite but for which aoxB sequences were not available are presented in black. The scale bar represents the average number of substitutions estimated per site.