Genome-Resolved Metagenomic Analysis of Groundwater: Insights into Arsenic Mobilization in Biogeochemical Interaction Networks

High-arsenic (As) groundwaters, a
worldwide issue, are critically
controlled by multiple interconnected biogeochemical processes. However,
there is limited information on the complex biogeochemical interaction
networks that cause groundwater As enrichment in aquifer systems.
The western Hetao basin was selected as a study area to address this
knowledge gap, offering an aquifer system where groundwater flows
from an oxidizing proximal fan (low dissolved As) to a reducing flat
plain (high dissolved As). The key microbial interaction networks
underpinning the biogeochemical pathways responsible for As mobilization
along the groundwater flow path were characterized by genome-resolved
metagenomic analysis. Genes associated with microbial Fe­(II) oxidation
and dissimilatory nitrate reduction were noted in the proximal fan,
suggesting the importance of nitrate-dependent Fe­(II) oxidation in
immobilizing As. However, genes catalyzing microbial Fe­(III) reduction
(omcS) and As­(V) detoxification (arsC) were highlighted in groundwater samples downgradient flow path,
inferring that reductive dissolution of As-bearing Fe­(III) (oxyhydr)­oxides
mobilized As­(V), followed by enzymatic reduction to As­(III). Genes
associated with ammonium oxidation (hzsABC and hdh) were also positively correlated with Fe­(III) reduction
(omcS), suggesting a role for the Feammox process
in driving As mobilization. The current study illustrates how genomic
sequencing tools can help dissect complex biogeochemical systems,
and strengthen biogeochemical models that capture key aspects of groundwater
As enrichment.