The 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, with the aim of improving our understanding of the phylogeny of As(III)-oxidizers in As-contaminated aquifers. As-oxidizing bacterial communities in As-enriched groundwater at different depths from Beimen were dominated by Betaproteobacteria (61%), Alphaproteobacteria (28%) and Gammaproteobacteria (11%); 78% As-oxidizers were observed in less As-enriched groundwater of Beimen 2B at 60 m depth while 17% As-oxidizers were observed in high As-enriched groundwater of Beimen 1 at 200 m depth. Pseudomonas sp. was found only in groundwater containing high arsenic levels at Beimen 1 and Beimen-Jinhu, while arsenite oxidizers belonging to Alpha- and Betaproteobacteria were dominated in groundwater containing low arsenic. Dissolved As concentration, Eh and oxygen levels were the important variables among several factors influencing As(III)-oxidizer abundance and diversity.
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