Another GeoChip 2.0 study examined groundwater microbial communities at a field site examining the use of acetate to stimulate U(VI)-reducing microorganisms in the subsurface at the Old Rifle site, a former U ore processing facility in Rifle CO (Liang www.frontiersin.org et al., 2012) . The study compared communities taken during a shift from sulfate to Fe(III)-reducing conditions. The overall community structure changed with the switch from Fe(III)to sulfate-reducing conditions and were reflective of the redox conditions at the site. Sulfate-reducing and methane-generating microorganisms increased in abundance under sulfate-reducing conditions. Acetate, U(VI) and redox potential were important environmental variables in determining the microbial community structure. Xie et al. (2011) examined five AMD sites in China using GeoChip 2.0 to determine the functional diversity and metabolic potential of microbial communities in these sites and to determine how the communities responded to environmental conditions. The sites showed a great deal of variability in regards to the microbial communities with ∼150-1000 functional genes detected in each sample. Most of the genes represented on the GeoChip that were involved in C, N, S cycling and metal resistance were detected in all of the AMD sites. Results indicated that the immediate environmental conditions were important in forming the variations in the functional structure of microbial communities as opposed to spatial distance. There was a positive correlation between Zn resistance gene abundance and Zn concentration but not for other metals. However, the concentrations of B, Co, Cu, La, Mg, and S were significantly correlated with the community structure in these communities. Overall, results suggested that AMD microbial communities may not be as simple as previously thought.