Isolation and characterization of arsenic resistant bacteria from tannery wastes and agricultural soils in Thailand

Highly arsenic resistant bacteria (27 isolates), which had a minimum inhibitory concentrations (MICs) for arsenite and arsenate of >= 40 mM and > 400 mM, respectively, were isolated from tannery wastes and agricultural soils collected in Central Thailand. On the basis of the morphological, cultural, physiological and biochemical characteristics, and on the principal ubiquinone component and 16S rRNA gene sequence analyses, they were identified as nine isolates each of Klebsiella (Groups 1 and 8) and Acinetobacter (Groups 2, 3 and 7), four isolates each of Pseudomonas (Groups 4 and 6) and Comamonas (Group 5), and one isolate of Enterobacter (Group 9). From these 27 isolates, only one isolate, A3-3 from the genus Comamonas, appeared potentially capable of oxidizing arsenite to arsenate, as determined by silver nitrate staining of arsenite agar plates after colony growth.