Abstract
Microbial metabolisms of arsenic, iron, sulfur, nitrogen and organic matter play important roles in arsenic mobilization in aquifer. In this study, microbial community composition and functional potentials in a high arsenic groundwater were investigated using integrated techniques of RNA- and DNA-based 16S rRNA gene sequencing, metagenomic sequencing and functional gene arrays. 16S rRNA gene sequencing showed the sample was dominated by members of Proteobacteria (62.3–75.2%), such as genera of Simplicispira (5.7–6.7%), Pseudomonas (3.3–5.7%), Ferribacterium (1.6–4.4%), Solimonas (1.8–3.2%), Geobacter (0.8–2.2%) and Sediminibacterium (0.6–2.4%). Functional potential analyses indicated that organics degradation, assimilatory sulfate reduction, As-resistant pathway, iron reduction, ammonification, nitrogen fixation, denitrification and dissimilatory nitrate reduction to ammonia were prevalent. The composition and function of microbial community and reconstructed genome bins suggest that high level of arsenite in the groundwater may be attributed to arsenate release from iron oxides reductive dissolution by the iron-reducing bacteria, and subsequent arsenate reduction by ammonia-producing bacteria featuring ars operon. This study highlights the relationship between biogeochemical cycling of arsenic and nitrogen in groundwater, which potentially occur in other aquifers with high levels of ammonia and arsenic.
Highlights
Arsenic (As) is a toxic metalloid and is widespread in the environment
The reductive dissolution mechanism only accounts for the initial trigger of arsenate release from iron oxides, but not for the transformation from arsenate to arsenite in reducing aquifers
It was reported that ammonium in groundwaters reflects degradation of organic matter and/or inputs of anthropogenic activities, such as fertilizers and manure, and only act on the formation of reducing conditions to favor the reductive dissolution of As-bearing Fe oxides[32,34,35]
Summary
Arsenic (As) is a toxic metalloid and is widespread in the environment. Elevated As in groundwater endangers the health of hundreds of millions of people worldwide, especially in Southern and Southeastern Asia[1,2]. The first mechanism commonly prevails in the late Pleistocene-Holocene aquifer systems with the sedimentation of fresh organic matter, such as inland basins from West Bengal, Bangladesh, Nepal, Cambodia, Vietnam and China, where degradation of organic matter fuels microorganisms to reduce and dissolve As-bearing iron oxides[4,10,11] Among those microbes, iron-reducing and sulfate-reducing bacteria are known to play important roles in As mobilization. The objective of this study is to further understand the microbial mobilization and transformation processes of As in groundwater, especially the role of nitrogen metabolism on As mobilization To this end, we used the integrated techniques of RNA- and DNA-based 16S rRNA gene sequencing, metagenomic sequencing and functional gene array (Geochip 4.0) to assess microbial community composition and functional potential in a high As groundwater. Our results indicated that some ammonium-producing bacteria with ars operon is likely to mediate the transformation from arsenate to arsenite in groundwater after it is released from the reductive dissolution of As-bearing iron oxides by iron-reducing bacteria
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
