Monitoring the activity of target microorganisms during stimulated 
bioremediation is a key problem for the development of effective remediation 
strategies. At the US Department of Energy's Integrated Field Research Challenge 
(IFRC) site in Rifle, CO, the stimulation of Geobacter growth and activity via 
subsurface acetate addition leads to precipitation of U(VI) from groundwater as 
U(IV). Citrate synthase (gltA) is a key enzyme in Geobacter central metabolism 
that controls flux into the TCA cycle. Here, we utilize shotgun proteomic 
methods to demonstrate that the measurement of gltA peptides can be used to 
track Geobacter activity and strain evolution during in situ biostimulation. 
Abundances of conserved gltA peptides tracked Fe(III) reduction and changes in 
U(VI) concentrations during biostimulation, whereas changing patterns of unique 
peptide abundances between samples suggested sample-specific strain shifts 
within the Geobacter population. Abundances of unique peptides indicated 
potential differences at the strain level between Fe(III)-reducing populations 
stimulated during in situ biostimulation experiments conducted a year apart at 
the Rifle IFRC. These results offer a novel technique for the rapid screening of 
large numbers of proteomic samples for Geobacter species and will aid monitoring 
of subsurface bioremediation efforts that rely on metal reduction for desired 
outcomes.