Abstract
High arsenic concentration in groundwater is a severe environmental problem affecting human health, particularly in countries of South and South-East Asia. The Bengal Delta Plain (BDP) distributed within India and Bangladesh is a major arsenic-affected region where groundwater is the primary source of drinking water. Previous studies have indicated that members of the bacterial class Betaproteobacteria constitute a major fraction of the microbial community in many of the aquifers within this region. Bacteria belonging to this class are known to be involved in redox cycling of arsenic as well as other metals such iron and manganese, thereby impacting arsenic mobilization and immobilization. While microbial diversity in arsenic-contaminated environments is generally assessed using universal 16S rRNA gene primers, targeted evaluation of Betaproteobacteria diversity remains poorly constrained. In this study, bacterial diversity was investigated in the groundwater from two shallow aquifers (West Bengal, India) based on 16S rRNA gene clone libraries and sequencing using a custom-designed pair of primers specific to Betaproteobacteria. Specificity of the primers was confirmed in silico as well as by the absence of PCR amplification of other bacterial classes. Four major families (Burkholderiaceae, Comamonadaceae, Gallionellaceae and Rhodocyclaceae) were detected among which members of Burkholderiaceae represented 59% and 71% of the total community in each aquifer. The four OTUs (operational taxonomic units; 97% sequence identity) within Burkholderiaceae were close phylogenetic relatives of bacteria within the genus Burkholderia known to solubilize phosphate minerals. Additionally, the OTUs belonging to Gallionellaceae were closely related to the members of the genera Gallionella and Sideroxydans, known to oxidize iron under microaerophilic conditions. These results suggest that members of Betaproteobacteria can potentially influence iron and phosphorus cycling which can influence biogeochemistry in arsenic-contaminated aquifers of the BDP.
Highlights
Elevated natural concentrations of arsenic (As) in groundwater is a major environmental health problem in many South and South-East Asian countries including India and Bangladesh, where consumption of As-contaminated water in the fertile Bengal Delta Plain (BDP) affects millions of people on a daily basis [1, 2]
Groundwater from the two shallow aquifers described above was re-sampled and clone library analyses were conducted using the above new pair of primers. These analyses showed that the Betaproteobacteria communities in both wells were massively dominated by members of the family Burkholderiaceae, which was not previously detected in these wells
The findings of this study demonstrate previously undetected diversity of Betaproteobacteria in the BDP wells by using a novel groupspecific set of primers
Summary
Elevated natural concentrations of arsenic (As) in groundwater is a major environmental health problem in many South and South-East Asian countries including India and Bangladesh, where consumption of As-contaminated water in the fertile Bengal Delta Plain (BDP) affects millions of people on a daily basis [1, 2]. The extent of contamination is greater in the shallow Holocene grey sand aquifers which supply majority of the drinking water in these regions, whereas groundwater in the deeper Pleistocene brown sand aquifers is largely known to be arsenic-free [3]. A number of environmental parameters such as biodegradable organic matter [7], iron [8], phosphate [9] and other electron acceptors [10, 11] have been shown to influence microbial arsenic cycling as well as groundwater microbial community composition and functions [12]. An in-depth understanding of the composition and distribution of indigenous microbial communities in BDP aquifers is crucial, in the context of developing cost-effective long-term arsenic mitigation strategies and for supply of arsenic free potable water
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