Toxicity of Uranium to Microbial Communities in Anaerobic Biofilms

Tapia-Rodríguez, Aida; Luna-Velasco, Antonia; Field, James A.; Sierra-Alvarez, Reyes

Toxicity of Uranium to Microbial Communities in Anaerobic Biofilms

2012

Tapia-Rodríguez, Aida | Luna-Velasco, Antonia | Field, James A. | Sierra-Alvarez, Reyes

Microbial processes have shown promise for the remediation of uranium and nitrate in groundwater impacted by uranium mine tailings. This study investigated the inhibitory impact of uranium(VI) towards different microbial populations in anaerobic biofilms, including methanogenic, denitrifying, and uranium-reducing microorganisms, which are commonly found at uranium bioremediation sites. Results of batch activity bioassays indicated a very distinct level of toxicity depending on the targeted microbial community. U(VI) caused severe inhibition of acetoclastic methanogenesis as indicated by a 50Â % inhibiting concentration (ICââ) of only 0.16Â mM. Denitrifying populations were also impacted by uranium, but their sensitivity depended on the electron donor utilized. Sulfur-oxidizing denitrifiers were the least affected (ICââ for denitrification activityâ=â0.32Â mM), followed by H₂- and acetate-utilizing denitrifiers (ICââ of 0.20 and 0.15Â mM, respectively). In contrast, exposure to U(VI) concentrations up to 1.0Â mM did not inhibit the rate of U(VI) bioreduction with H₂ as electron donor in the presence or absence of nitrate. On the contrary, a considerable increase in the uranium-reducing activity of the denitrifying and methanogenic mixed cultures was observed with increasing uranium concentrations. The results suggest that microorganisms responsible for U(V) reduction could tolerate much higher uranium concentrations compared to the other microbial populations assayed.

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