TY - JOUR
T1 - Coupled mercury-cell sorption, reduction, and oxidation on methylmercury production by Geobacter sulfurreducens PCA
AU - Lin, Hui
AU - Morrell-Falvey, Jennifer L.
AU - Rao, Balaji
AU - Liang, Liyuan
AU - Gu, Baohua
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/10/21
Y1 - 2014/10/21
N2 - G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell-SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10-19 to 25 × 10-19 moles-Hg/cell (equivalent to Hg/cell-SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ΔomcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn2+ leads to increased Hg reduction and decreased methylation. These results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments.
AB - G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell-SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10-19 to 25 × 10-19 moles-Hg/cell (equivalent to Hg/cell-SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ΔomcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn2+ leads to increased Hg reduction and decreased methylation. These results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments.
UR - http://www.scopus.com/inward/record.url?scp=84908136428&partnerID=8YFLogxK
U2 - 10.1021/es502537a
DO - 10.1021/es502537a
M3 - Article
C2 - 25268220
AN - SCOPUS:84908136428
SN - 0013-936X
VL - 48
SP - 11969
EP - 11976
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 20
ER -