ABSTRACT
This study evaluated the influence of changes in the microbial community structure on reoxidation of reduced uranium during a postbiostimulation period. Effluent groundwater from acetate-stimulated sediment flow-through columns was analyzed over 60 days after acetate amendment was discontinued. Only a small reoxidation of iron or uranium (17%) occurred in the presence of 1-2 mg L(-1) O(2) influent groundwater for the 2-month period. Most uranium reoxidation occurred during the first 2 weeks after biostimulation with acetate was discontinued. Groundwater and sediment microbial community compositions suggested that two processes played important roles immediately after the cessation of acetate addition. The first process was characterized by a predominance of both sediment-bound and planktonic microorganisms most closely related to Hydrogenophaga sp., Thiobacillus sp., and Gallionella sp., which could oxidize a variety of reduced compounds. The second process was characterized by organisms closely related to Lysobacter sp. and Sterolibacterium sp., with the potential to feed on complex organic compounds from biomass turnover. The presence of these bacteria and the lack of uranium oxidation implied that after acetate addition was stopped, reduced inorganic compounds and dead biomass became electron donors for a microbial community capable of using low ambient oxygen as a terminal electron acceptor, contributing to the preservation, at least temporarily, of biogenic U(IV).
