FIG 1.

Maximum likelihood phylogenetic tree based on partial sequences (∼330 bp) of the 61,333 total arsenate reductase (arrA) genes sequenced, representing 253 phylotypes (each containing >5 sequences), and of 762 arrA gene sequences, from cultured or uncultured organisms, in GenBank. The sequences were collapsed into major phylogenetic clusters at 85% DNA identity, and relative distributions of arrA gene sequences determined in the current study or obtained from GenBank are reported. Black triangles, clusters containing sequences from pure culture isolates; gray triangles, clusters containing sequences from uncultured organisms from GenBank; white triangles, clusters unique to this study. Numbers at the branch nodes reflect the maximum likelihood bootstrap support values. The psrA gene from Wolinella succinogenes (GenBank accession no. X65042) was used as an outgroup. Detailed distributions of arrA gene sequences from GenBank are presented in Tables S3 and S4.