To better understand the microbial functional diversity changes with subsurface 
redox conditions during in situ uranium bioremediation, key functional genes 
were studied with GeoChip, a comprehensive functional gene microarray, in field 
experiments at a uranium mill tailings remedial action (UMTRA) site (Rifle, CO). 
The results indicated that functional microbial communities altered with a shift 
in the dominant metabolic process, as documented by hierarchical cluster and 
ordination analyses of all detected functional genes. The abundance of dsrAB 
genes (dissimilatory sulfite reductase genes) and methane generation-related mcr 
genes (methyl coenzyme M reductase coding genes) increased when redox conditions 
shifted from Fe-reducing to sulfate-reducing conditions. The cytochrome genes 
detected were primarily from Geobacter sp. and decreased with lower subsurface 
redox conditions. Statistical analysis of environmental parameters and 
functional genes indicated that acetate, U(VI), and redox potential (E(h)) were 
the most significant geochemical variables linked to microbial functional gene 
structures, and changes in microbial functional diversity were strongly related 
to the dominant terminal electron-accepting process following acetate addition. 
The study indicates that the microbial functional genes clearly reflect the in 
situ redox conditions and the dominant microbial processes, which in turn 
influence uranium bioreduction. Microbial functional genes thus could be very 
useful for tracking microbial community structure and dynamics during 
bioremediation.