Geochemistry and Bioremediation Implications of Indigenous Arsenite-Oxidizing Bacteria from Arsenic-Contaminated Aquifers of the Upper Ganga Plain

Abstract

Laksar, located in the upper Ganga plains of Haridwar, is an agro-intensive area where arsenic (As) contamination of groundwater has recently been reported. A seasonal investigation was conducted across Laksar to evaluate the geochemistry and microbiology of shallow unconfined groundwater aquifers. Total As concentrations in groundwater ranged from 3.5 to 78 μg L–1, frequently exceeding the permissible limits for drinking water. Redox conditions of aquifers varied seasonally but remained largely oxidizing and averaged 216 ± 167 mV. As concentrations showed no significant seasonal variations (p = 0.369), indicating dominant control by localized site-specific hydrogeochemical conditions (σ2 = 0.80). Several indigenous heterotrophic bacterial strains showed tolerance to high As(III) concentrations of ∼10.3 mM (∼1 g L–1) and promising potential to oxidize As(III). Potential As(III) oxidizing strains belonged to the genera Acinetobacter, Stenotrophomonas, Bacillus, Rhodococcoides, Brevundimonas, and Nocardioides based on 16S rRNA gene analysis. In synthetic simulated groundwater conditions, biomass-normalized rates of selected As(III) oxidizing strains varied between ∼0.1 and 0.6 mM As(III) mg–1 d–1. Our findings importantly highlight the implications of indigenous As(III) oxidizing strains under simulated groundwater conditions for developing site-specific and sustainable bioremediation strategies.