In GM1 arsenite oxidase expression is also constitutive when grown in the absence of

arsenite [i.e. in the MSM with 0.04% (w/v) yeast extract] with 0.367 U/mg observed in late exponential phase and activity also detected in early exponential phase (0.13 U/mg). Taken together this information suggests that there are at least two modes of regulating the expression of the aro genes in GM1, possibly a two-component signal transduction system and quorum sensing. Because of the broad temperature range for growth of GM1, arsenite oxidase activity was determined at a variety of temperatures selleck compound (Figure 4). Activity occurred over a broad temperature range reaching a maximum at temperatures well above the optimum for growth (i.e. between 40-50°C). Figure 4 Specific activity

of GM1 arsenite oxidase as a function of temperature. Error bars are the standard deviation of multiple assays. The partial aroA gene sequence of GM1 was found to be identical to that of the partial aroA of the putative arsenite oxidiser Limnobacter sp. 83, another member of the Betaproteobacteria [8] but in a different family. No homologues of aroA were found in the genome sequences of GM1′s closest relatives, Polaromonas naphthalenivorans CJ2 and Polaromonas sp. JS666; www.selleckchem.com/screening/mapk-library.html GM1 is thus clearly distinct from the other Polaromonas spp. To compare the arsenite oxidisers in the top (9.22 mM arsenite) and bottom (6.01 mM arsenite) subsamples from the 2007 biofilm, two aroA gene libraries were constructed using a recently developed method [7]. The use of aroA-specific primers has been shown to be a useful approach for detecting and identifying arsenite oxidisers in environmental samples [7–10, 19]. Phylogenetic analysis of 100 AroA-like sequences (Figure

5), from 50 top (designated TOP) and 50 bottom (designated BOT) clones, revealed the diversity of arsenite-oxidising bacteria in the two subsamples. The corresponding protein sequences were compared with known and putative AroA sequences and with the sequence obtained from GM1. Eighteen different AroA-like sequences were obtained from the TOP library and ten from BOT; only four were present in both. All but one of the sequences clustered within C1GALT1 the Betaproteobacteria; the exception, BOT10, clustered within the Agrobacterium/Rhizobium branch of the Alphaproteobacteria. The TOP8 sequence is closely related (98.7% sequence identity) to the AroA homologue in Akt tumor Rhodoferax ferrireducens. Apart from BOT10 the AroA-like sequences clustered into three distinct clades (A, B and C), none of which is close to any AroA sequences from known arsenite oxidisers. The BOT7 sequence (clade C) was identical to the AroA sequence of GM1, so the other sequences in clade C may also come from Polaromonas species. The affinities of the organisms whose AroA sequences lie in clades A and B are not known. Figure 5 Phylogenetic tree of AroA-like sequences from an arsenic-contaminated biofilm.