A novel heterotrophic arsenite-oxidizing bacterium isolated from arsenic-polluted groundwater of Lombardia (Italy)

Arsenic contamination of aquifers is a threat to human health and the World Health Organization recommends 10 μgL-1 as the maximum arsenic concentration in drinking water. Groundwater of Lombardia (Italy) has been found to contain arsenic concentrations higher than the limit due to the substratum rock types of the site. Within a project, aimed to study the indigenous microbial communities of As-rich groundwater from Lombardia, we isolated an heterotrophic bacterium (strain 2WW) able to oxidise As(III). Here we present the characterization of this strain by evaluating the growth and As(III)-oxidation rate at different pH and temperature, and by investigating the presence of arsenic genes. Based on 16S rRNA gene sequence analysis, strain 2WW was most closely related to Aliihoeflea estuarii, affiliated to the Alphaproteobacteria. It completely oxidized 1 mM As(III) within 24 h at 30°C, and within 96 h at 15° C. At 5°C the complete oxidation of As(III) occurred in 350 h. Complete As(III) oxidation occurred also in the pH range 5.0-8.0. The strain carried an arsenite oxidase (aioA) gene highly similar to those of Rhizobiales, and an arsenite efflux pump (ACR3(2)) gene highly similar to the arsenite transporter of Hoeflea sp strain CH14. For the first time, we provided evidence for the presence of an aioA gene in a bacterium affiliated to genus Aliihoeflea genus and for its As(III)-oxidizing capability. The bacterial As(III)-oxidation is being a promising first step in the removal of arsenic from groundwater, in combination with adsorbents. Research supported by CARIPLO Foundation, project 2010-2221