Aims: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors.
Methods and results: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25 degrees C. As(III) oxidation was still observed in the presence of 1000 mg l(-1) As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l(-1) h(-1). The CASO1 consortium contains at least two organisms - strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5.9%, suggesting that b6 may be a new species.
Conclusions: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment.
Significance and impact of the study: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.