Isolation of an arsenate-respiring bacterium from a redox front in an arsenic-polluted aquifer in West Bengal, Bengal Basin.

Thomas H Osborne,Pradip K Sikdar,Joanne M Santini,John M Mcarthur

doi:10.1021/es504707x

Abstract

Natural pollution of groundwater by arsenic adversely affects the health of tens of millions of people worldwide, with the deltaic aquifers of SE Asia being particularly polluted. The pollution is caused primarily by, or as a side reaction of, the microbial reduction of sedimentary Fe(III)-oxyhydroxides, but the organism(s) responsible for As release have not been isolated. Here we report the first isolation of a dissimilatory arsenate reducer from sediments of the Bengal Basin in West Bengal. The bacterium, here designated WB3, respires soluble arsenate and couples its reduction to the oxidation of acetate; WB3 is therefore implicated in the process of arsenic pollution of groundwater, which is largely by arsenite. The bacterium WB3 is also capable of reducing dissolved Fe(III) citrate, solid Fe(III)-oxyhydroxide, and elemental sulfur, using acetate as the electron donor. It is a member of the Desulfuromonas genus and possesses a dissimilatory arsenate reductase that was identified using degenerate polymerase chain reaction primers. The sediment from which WB3 was isolated was brown, Pleistocene sand at a depth of 35.2 m below ground level (mbgl). This level was some 3 cm below the boundary between the brown sands and overlying reduced, gray, Holocene aquifer sands. The color boundary is interpreted to be a reduction front that releases As for resorption downflow, yielding a high load of labile As sorbed to the sediment at a depth of 35.8 mbgl and concentrations of As in groundwater that reach >1000 μg/L.

Highlights

Concentrations of dissolved arsenic (As) in groundwater of deltaic aquifers of SE Asia often exceed 10 μg/L, the World Health Organization’s guideline value for As in drinking water.[1,2] The As hazard is most severe in the shallow aquifers of Bangladesh and West Bengal, typically at depths
Shallow groundwaters of the Bengal Basin usually contain mg/L of dissolved iron (Fe) as well as As.[9−12] In groundwater worldwide, the presence of aqueous Fe is due to dissimilatory reduction of sedimentary Fe(III)-oxyhydroxides by indigenous bacteria that couple its reduction to the oxidation of organic matter.[13]
The interface between gray and brown sand was at 35.2 mbgl and captured in two cores (SI Figure S2)

Summary

Introduction

Concentrations of dissolved arsenic (As) in groundwater of deltaic aquifers of SE Asia often exceed 10 μg/L, the World Health Organization’s guideline value for As in drinking water.[1,2] The As hazard is most severe in the shallow aquifers of Bangladesh and West Bengal (the Bengal Basin), typically at depths

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Results

Conclusion