Phylogenetic tree of AroA-like sequences from an arsenic-contaminated biofilm. Phylogenetic analysis of 50 AroA-like sequences from both the top (TOP) and bottom (BOT) of the biofilm. Published AroA sequences are in bold, organisms that contain AroA homologues and the AroA from the arsenite-oxidising bacterium GM1 are also shown. Numbers in parentheses indicate the number of identical sequences represented by each branch. Significant bootstrap values (per 100 trials) of major branch points are shown. Closely related groups of sequences have been designated clades A, B and C. Putative AroA sequences from the Archaea were used to root the tree.