Bacterial Communities in Bangladesh Aquifers Differing in Aqueous Arsenic Concentration

Abstract

At Titas, Bangladesh, two aquifers of different arsenic concentrations and redox conditions were investigated to link variations in geochemistry to in situ bacterial diversity characterized by T-RFLP (terminal restriction fragment length polymorphism) and clone library analysis. While the shallow aquifer was characterized by reduced gray sediments with a higher share of easily mobilized sedimentary arsenic (2.6% was easily mobilized from 18 mg/kg of total arsenic available in sediments) and higher aqueous arsenic concentrations of 120 ± 6 μg/L (45% arsenite), the deeper aquifer consisted of brown oxidized sediments with lower aqueous arsenic concentrations, predominantly as arsenate (60 ± 6 μg/L; 3% arsenite) and a higher share of tightly bound arsenic (only 0.6% of 53 mg/kg total sorbed arsenic was easily mobilized). The bacterial communities of both aquifers were dominated by putative aerobic or denitrifying populations of Pseudomonas, Elizabethkingia and Pantoea. The shallow aquifer was more diverse in bacterial populations of aerobic, facultative and anaerobic bacteria, an observation which may be correlated to more variable geochemical conditions resulting in arsenic mobilization and re-sorption. The deeper aquifer showed higher abundance of aerobic bacterial populations including the presence of iron-oxidizing Sideroxydans possibly of importance for the sorption of arsenic on oxidized iron hydroxides. From the arsenic-affected shallow aquifer, As(III) oxidizing isolates of Comamonas and Microbacterium were obtained, which may provide information on suitable conditions for arsenic immobilization useful for future bioremediation efforts. Supplemental materials are available for this article. Go to the publisher’s online edition of Geomicrobiology Journal to view the free supplemental file.

Keywords:

• Arsenic contamination
• Bangladesh
• Microbial community analysis
• T-RFLP
• As(III) oxidation

ACKNOWLEDGMENTS

M. Sultana was supported by a grant from DAAD. Field studies and sample collection were funded by the German Research Foundation (grant PL 302/2-1 to B. Planer-Friedrich). The authors would like to thank professor S.I. Khan of the Department of Microbiology, University of Dhaka, and Professor Qumrul Hassan of the Department of Geology, University of Dhaka, for their cooperation during sample collection and initial processing. Additional thanks, are due to Beate Erler, Christine Moschner and Nadja Muth of the Interdisciplinary Ecological Center, TU Bergakademie Freiberg, for their assistance in clone library construction and to Dr. Anne-Christine Schmidt of the Institute of Analytical Chemistry, TU Bergakademie Freiberg, for arsenite measurements.