Diversity of arsenite oxidizing bacterial communities in arsenic-rich deltaic aquifers in West Bengal, India

Abstract

High arsenic (As) concentration in groundwater has affected human health, particularly in South-East Asia putting millions of people at risk. Biogeochemical cycling of As carried out by different bacterial groups are suggested to control the As fluxes in aquifers. A functional diversity approach in link with As precipitation was adopted to study bacterial community structures and their variation within the As contaminated Bengal Delta Plain (BDP) aquifers of India. Groundwater samples collected from two shallow aquifers in Karimpur II (West Bengal, India), during years 2010 and 2011, were investigated to trace the effects immediately after monsoon period (precipitation) on community structure and diversity of bacterial assemblages with a focus on arsenite oxidizing bacterial phyla for two successive years. The study focused on amplification, clone library generation and sequencing of the arsenite oxidase large sub-unit gene aioA and 16S rRNA marker, with respect to changes in elemental concentrations. New set of primers were designed to amplify the aioA gene as a phylogenetic marker to study taxonomically diverse arsenite oxidizing bacterial groups in these aquifers. The overall narrow distribution of bacterial communities based on aioA and 16S rRNA sequences observed was due to poor nutrient status and anoxic conditions in these As contaminated aquifers. Proteobacteria was the dominant phylum detected, within which Acidovorax, Hydrogenophaga, Albidiferax, Bosea, and Polymorphum were the major arsenite oxidizing bacterial genera based on the number of clones sequenced. The structure of bacterial assemblages including those of arsenite oxidizing bacteria seems to have been affected by increase in major elemental concentrations (e.g., As, Fe, S, and Si) within two sampling sessions, which was supported by statistical analyses. One of the significant findings of this study is detection of novel lineages of 16S rRNA-like bacterial sequences indicating presence of indigenous bacterial communities BDP wells that can play important role in biogeochemical cycling of elements including As.

Keywords: Arsenic; aioA gene; aquifer; arsenite oxidation; phylogeny.

Figure 1

Map showing sampling locations in Nadia district (West Bengal, India).

Figure 2

Temporal trends of important As(III) oxidizing bacterial groups studied in the two wells 28 and 204 for two consecutive years (2010 and 2011).

Figure 3

Temporal trends of major bacterial groups studied in the two wells 28 and 204 for two consecutive years (2010 and 2011).

Figure 4

Rarefaction curves from DOTUR analysis using furthest neighbor assignment algorithm with the aioA related amino acid sequences retrevied from wells 28 and 204 for the two years (2010 and 2011) at 0.02 evolutionary distance.

Figure 5

Phylotype frequency curve for 229 aioA sequences distributed among 16 phylotypes.

Figure 6

Rarefaction curves from DOTUR analysis using furthest neighbor assignment algorithm with the 16S rRNA gene sequences retrevied from wells 28 and 204 for the two years (2010 and 2011) at 0.03 evolutionary distance.

Figure 7

Phylotype frequency curve for 169 16S rRNA sequences distributed among 18 phylotypes.