Abstract
The importance of bacteria in the anaerobic bioremediation of groundwater polluted with organic and/or metal contaminants is well recognized and in some instances so well understood that modeling of the in situ metabolic activity of the relevant subsurface microorganisms in response to changes in subsurface geochemistry is feasible. However, a potentially significant factor influencing bacterial growth and activity in the subsurface that has not been adequately addressed is protozoan predation of the microorganisms responsible for bioremediation. In field experiments at a uranium-contaminated aquifer located in Rifle, CO, USA, acetate amendments initially promoted the growth of metal-reducing Geobacter species, followed by the growth of sulfate reducers, as observed previously. Analysis of 18S rRNA gene sequences revealed a broad diversity of sequences closely related to known bacteriovorous protozoa in the groundwater before the addition of acetate. The bloom of Geobacter species was accompanied by a specific enrichment of sequences most closely related to the ameboid flagellate, Breviata anathema, which at their peak accounted for over 80% of the sequences recovered. The abundance of Geobacter species declined following the rapid emergence of B. anathema. The subsequent growth of sulfate-reducing Peptococcaceae was accompanied by another specific enrichment of protozoa, but with sequences most similar to diplomonadid flagellates from the family Hexamitidae, which accounted for up to 100% of the sequences recovered during this phase of the bioremediation. These results suggest a prey–predator response with specific protozoa responding to increased availability of preferred prey bacteria. Thus, quantifying the influence of protozoan predation on the growth, activity and composition of the subsurface bacterial community is essential for predictive modeling of in situ uranium bioremediation strategies.
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Acknowledgements
Research at the University of Massachusetts was funded by the Office of Science (BER), US Department of Energy, Awards no. DE-SC0004080 and DE-SC0004814 and Cooperative Agreement no. DE-FC02-02ER63446. Additional support for field research was equally supported through the Integrated Field Research Challenge Site (IFRC) at Rifle, CO, USA and the Lawrence Berkeley National Laboratory’s Sustainable Systems Scientific Focus Area. The US Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research funded the work under contract DE-AC02-05CH11231 (Lawrence Berkeley National Laboratory; operated by the University of California).
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Holmes, D., Giloteaux, L., Williams, K. et al. Enrichment of specific protozoan populations during in situ bioremediation of uranium-contaminated groundwater. ISME J 7, 1286–1298 (2013). https://doi.org/10.1038/ismej.2013.20
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