Abundance and diversity of methanogens: Potential role in high arsenic groundwater in Hetao Plain of Inner Mongolia, China

To investigate the community diversity and abundance of methanogens and their potential role in high arsenic groundwater, 17 groundwater samples from Hetao Plain of Inner Mongolia were investigated with an integrated method including 16S rRNA gene clone library, quantitative polymerase chain reaction and geochemistry analyses. Total arsenic (AsTot) concentrations were 82.7-1088.7 μg/L and arsenite (AsIII) mostly dominated in these samples with percentages of 0.04-0.79. CH4 concentrations ranged from 0.01 to 292 μg/L and distinctly elevated only when AsTot were relatively high and SO42 − were distinctly low. Principal component analysis indicated that these samples were divided into three groups according to the variations of AsTot, CH4 and SO42 −. AsTot concentrations were distinctly high in the group with high CH4 and low SO42 − comparing to the other two groups (one with high CH4 and high SO42 −, the other with low CH4 and SO42 −). The mcrA gene (methyl coenzyme-M reductase gene) based phylogenetic analysis of methanogens population showed that methanogenic archaea was diverse but mainly composed of Methanomicrobiales, Methanosarcinales, Methanobacteria and unidentified groups, with Methanomicrobiales being distinctly dominant (50.6%). The mcrA gene abundance in high arsenic groundwater ranged from 3.01 × 103 to 3.80 × 106 copies/L and accounted for 0-30.2% of total archaeal 16S rRNA genes. The abundance of mcrA genes was positively correlated with the concentrations of AsTot (R = 0.59), AsIII (R = 0.57) and FeII (R = 0.79), while it was negatively correlated with oxidation-reduction potential (R = − 0.66) and SO42 − concentration (R = − 0.64). These results implied that methanogenic archaea might accelerate As release in groundwater aquifers in Hetao Plain.