Zhou, and six co-authors report that 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 16SrRNA gene sequencing, metagenomic sequencing and functional gene arrays. 16SrRNA 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, ammonifcation, nitrogen fixation, denitrification and dissimilar 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, a unit made up of linked genes which is thought to regulate other genes responsible for protein synthesis. 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.
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, The widespread problem of high levels of As in groundwater prompts intensive studies from multi-disciplinary
research fields, such as geochemistry, hydrology, mineralogy, microbiology and ecology, to understand the hydro-biogeochemical behaviors of As in global aquifer systems. To date, three main mechanisms have been proposed for As mobilization in groundwater: (1) the reductive dissolution of As-bearing iron (Fe) oxides under reducing conditions, (2) the oxidative dissolution of As-bearing pyrite and arsenopyrite under oxidizing conditions, and (3) the competitive adsorption between As and phosphate/bicarbonate under alkaline conditions.
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. Among those microbes, iron-reducing and sulfate-reducing bacteria are known to play important roles in As mobilization. For example, dissimilar iron-reducing bacteria, such as Geobacter sp. and Shewanella sp., could directly utilize organic carbon as electron sources to reduce As-bearing iron oxides, leading to As release or re immobilization by forming secondary iron minerals, such as vivianite and magnetite. Sulfide generated by sulfate-reducing bacteria in aquifers abiotically reduces As-bearing iron oxides to mobilize As.
If derived ferrous iron is sufficiently available in groundwater, sulfide could form iron-sulfide minerals to further sequester As through co-precipitation and/or adsorption. However, 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. Previous studies based on arrA gene coding respiratory arsenate reductase large sub-unit highlight the role of dissimilar arsenate-respiring bacteria on arsenate transformation.
Managed & Built by I2M Consulting, LLC | © 2010-
