Arsenic-hypertolerant and arsenic-reducing bacteria isolated from wells in Tucumán, Argentina

Arsenic-hypertolerant bacteria were isolated from arsenic-contaminated well water from the village of Los Pereyra in Tucumán province, Argentina. Microorganisms that biotransform arsenic are a major factor in arsenic mobilization in contaminated aquifers. Groundwater analyses showed a level of arsenic contamination (mean concentration of 978 μg·L^-1) that exceeds the safe drinking water limit of 10 μg·L^-1 recommended by the World Health Organization and the Argentine Food Code. There was considerable spatial variability in the concentration of arsenic in each of the wells analyzed and in the distribution of the major anions HCO₃^-, SO₄^2-, and Cl^-. Eighteen bacterial strains were characterized. Six strains belonging to the Actinobacteria phylum were able to grow in media with 20 mmol·L^-1 As(III) or 200 mmol·L^-1 As(V) and were also highly resistant to Cr, Cd, and Cu. Their ability to biotransform arsenic was examined by speciation of the products by high-performance liquid chromatography inductively coupled plasma mass spectrometry. In addition, two strains, Brevibacterium sp. strain AE038-4 and Microbacterium sp. strain AE038-20, were capable of aerobic arsenate reduction, which suggests that these strains could increase the mobility of arsenic by formation of more mobile As(III).