Postbiostimulation microbial community structure changes that control the reoxidation of uranium

Area of Science:

• Environmental microbiology
• Geochemistry
• Bioremediation

Background:

• Acetate biostimulation is used to reduce uranium in groundwater.
• Understanding post-biostimulation microbial dynamics is crucial for uranium immobilization.
• The fate of reduced uranium after cessation of stimulation requires further investigation.

Purpose of the Study:

• To evaluate the impact of microbial community structure changes on uranium reoxidation after acetate biostimulation.
• To identify key microbial processes governing uranium fate during the post-stimulation period.
• To determine the duration of uranium preservation under specific environmental conditions.

Main Methods:

• Analysis of effluent groundwater from acetate-stimulated sediment flow-through columns over 60 days.
• Monitoring of uranium and iron reoxidation.
• Characterization of groundwater and sediment microbial community composition using molecular methods.

Main Results:

• Limited uranium and iron reoxidation (17%) occurred despite the presence of low dissolved oxygen (1-2 mg L(-1)).
• The majority of uranium reoxidation happened within the first two weeks after acetate amendment ceased.
• Microbial communities shifted, with initial dominance of inorganic compound oxidizers (Hydrogenophaga, Thiobacillus, Gallionella) followed by biomass degraders (Lysobacter, Sterolibacterium).

Conclusions:

• Post-biostimulation microbial communities utilized reduced inorganic compounds and dead biomass as electron donors.
• These microbial activities, coupled with low oxygen availability, contributed to the temporary preservation of biogenic U(IV).
• The findings highlight the complex interplay between microbial ecology and uranium geochemistry in remediated environments.