Depth-resolved abundance and diversity of arsenite-oxidizing bacteria in the groundwater of Beimen, a blackfoot disease endemic area of southwestern Taiwan Suvendu Das a , Sandeep Kar a , Jiin-Shuh Jean a, *, Jagat Rathod b , Sukalyan Chakraborty a , Hsiao-Sheng Liu c , Jochen Bundschuh d a Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan b Department of Microbiology and Biotechnology Centre, The Maharaja Sayajirao University of Baroda, Vadodara 390002, Gujarat, India c Department of Microbiology and Immunology, Medical College, National Cheng Kung University, Tainan, Taiwan d National Centre for Engineering in Agriculture, University of Southern Queensland, Toowoomba, Australia article info Article history: Received 7 March 2013 Received in revised form 3 July 2013 Accepted 22 July 2013 Available online 20 October 2013 Keywords: Groundwater arsenic Arsenite oxidizing bacteria PCR-DGGE MPN-PCR abstract The role of arsenite oxidizers in natural attenuation of arsenic pollution necessitates studies on their abundance and diversity in arsenic-contaminated aquifers. In this study, most probable number-polymerase chain reaction (MPN-PCR) and denaturing gradient gel electrophoresis (DGGE) was applied to monitor depth-wise abundance and diversity of aerobic arsenite oxidizers in arsenic-enriched groundwater of Beimen, southwestern Taiwan. The results revealed that the abundance of arsenite oxidizers ranged from 0.04 to 0.22, and the lowest ratio was observed in the most arsenic-enriched and comparatively more reduced groundwater (depth 200 m) of Beimen 1. The highest ratio was observed in the less arsenic-enriched and less reduced groundwater (depth 60 m) of Beimen 2B. DGGE profiles showed a shift in diversity of arsenite oxidizers, consisting of members of the Betaproteobacteria (61%), Alphaproteobacteria (28%) and Gammaproteobacteria (11%), depending on mainly arsenic concentration and redox level in groundwater. Groundwater with the lowest arsenic and highest dissolved oxygen at Beimen 2B harbored 78% of the arsenite oxidizers communities, while groundwater with the highest arsenic and lowest dissolved oxygen at Beimen 1 and BeimeneJinhu harbored 17 and 22% of arsenite oxidizers com- munities, respectively. Pseudomonas sp. was found only in groundwater containing high arsenic at Beimen 1 and BeimeneJinhu, while arsenite oxidizers belonging to Alpha- and Betaproteobacteria were dominated in groundwater containing low arsenic. ª 2013 Elsevier Ltd. All rights reserved. 1. Introduction Arsenic (As), the toxic metalloid, is ubiquitous in many envi- ronments, but is not uniformly distributed in alluvial aquifers. The concentration of As differs considerably, depending on the geochemical characteristics of the aquifers and related biogeochemical processes. Solid phase As is found to be co- precipitated in or co-adsorbed on a number of minerals in * Corresponding author. Tel.: þ886 6 2757575x65426; fax: þ886 6 274 0285. E-mail address: jiinshuh@mail.ncku.edu.tw (J.-S. Jean). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/watres water research 47 (2013) 6983 e6991 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.07.049