Vanadium respiration by Geobacter metallireducens: novel strategy for in situ removal of vanadium from groundwater

Abstract

Vanadium can be an important contaminant in groundwaters impacted by mining activities. In order to determine if microorganisms of the Geobacteraceae, the predominant dissimilatory metal reducers in many subsurface environments, were capable of reducing vanadium(V), Geobacter metallireducens was inoculated into a medium in which acetate was the electron donor and vanadium(V) was the sole electron acceptor. Reduction of vanadium(V) resulted in the production of vanadium(IV), which subsequently precipitated. Reduction of vanadium(V) was associated with cell growth with a generation time of 15 h. No vanadium(V) was reduced and no precipitate was formed in heat-killed or abiotic controls. Acetate was the most effective of all the electron donors evaluated. When acetate was injected into the subsurface to enhance the growth and activity of Geobacteraceae in an aquifer contaminated with uranium and vanadium, vanadium was removed from the groundwater even more effectively than uranium. These studies demonstrate that G. metallireducens can grow via vanadium(V) respiration and that stimulating the activity of Geobacteraceae, and hence vanadium(V) reduction, can be an effective strategy for in situ immobilization of vanadium in contaminated subsurface environments.

FIG. 1.

Cell growth and vanadium(V) concentrations when G. metallireducens that had been previously grown in acetate-vanadium(V) medium was inoculated into a freshwater medium with 10 mM acetate as the electron donor and 1 mM vanadium(V) as the electron acceptor. Results are the means and standard deviations for triplicate cultures.

FIG. 2.

Precipitation of vanadium as the result of vanadium(V) reduction.

FIG. 3.

X-Ray energy spectrum of the vanadium precipitate obtained via electron microprobe analysis.

FIG. 4.

Vanadium(V) in groundwater samples within the monitoring-well field. B-01 to B-03, upgradient control wells; M-01 to M-15, monitoring wells downgradient from the point of acetate injection. Groundwater flow is from left to right, and the injection gallery is positioned between the control wells and the first row of monitoring wells.