Inhibitory effect of nitrate/nitrite on the microbial reductive dissolution of arsenic and iron from soils into pore water.

It was well established that microbial communities are the major drive for the formation of arsenic-contaminated groundwater. However, it remains to be elucidated for how nitrate/nitrite affects the microorganisms-catalyzed dissolution and reduction of arsenic. To address this issue, we collected soil samples containing high-contents of arsenic from the Shimen Realgar Mine area. Microcosm assay indicated that addition of nitrate/nitrite significantly inhibited the dissolution, reduction and release of As and Fe caused by the biological catalysis of microbial communities in the soils, meanwhile nitrate/nitrite was reduced into N. To further investigate the molecular mechanism of this finding, we used a representative dissimilatory arsenate-respiring strain Shewanella sp. GL90 from the soils to perform the arsenic release assay. GL90 can efficiently catalyze the reductive dissolution, and promote the release of As and Fe in soils. It is interesting to see that the addition of nitrate/nitrite to the soils led to marked decreases in the GL90-mediated dissolution of As and Fe in the soils. Moreover, we found that this finding was attributed to that nitrate/nitrite significantly inhibited the transcription of the gene of the respiratory arsenate reductase protein in GL90 cells. This work provided new insights into the mechanisms for the coupling of As, N and Fe geochemical cycles in arsenic-rich soils, and for how environmental factors affect As concentration in groundwater.