ORCID Profile
0000-0002-1838-8942
Current Organisation
California Department of Water Resources
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Publisher: Springer Science and Business Media LLC
Date: 24-06-2013
Abstract: The erse microbial populations that inhabit pristine aquifers are known to catalyze critical in situ biogeochemical reactions, yet little is known about how the structure and ersity of this subsurface community correlates with and impacts upon groundwater chemistry. Herein we examine 8,786 bacterial and 8,166 archaeal 16S rRNA gene sequences from an array of monitoring wells in the Mahomet aquifer of east-central Illinois. Using multivariate statistical analyses we provide a comparative analysis of the relationship between groundwater chemistry and the microbial communities attached to aquifer sediment along with those suspended in groundwater. Statistical analyses of 16S rRNA gene sequences showed a clear distinction between attached and suspended communities with iron-reducing bacteria far more abundant in attached s les than suspended, while archaeal clones related to groups associated with anaerobic methane oxidation and deep subsurface gold mines (ANME-2D and SAGMEG-1, respectively) distinguished the suspended community from the attached. Within the attached bacterial community, cloned sequences most closely related to the sulfate-reducing Desulfobacter and Desulfobulbus genera represented 20% of the bacterial community in wells where the concentration of sulfate in groundwater was high ( 0.2 mM), compared to only 3% in wells with less sulfate. Sequences related to the genus Geobacter , a genus containing ferric-iron reducers, were of nearly equal abundance (15%) to the sulfate reducers under high sulfate conditions, however their relative abundance increased to 34% when sulfate concentrations were 0.03 mM. Also, in areas where sulfate concentrations were .03 mM, archaeal 16S rRNA gene sequences similar to those found in methanogens such as Methanosarcina and Methanosaeta comprised 73–80% of the community, and dissolved CH 4 ranged between 220 and 1240 μM in these groundwaters. In contrast, methanogens (and their product, CH 4 ) were nearly absent in s les collected from groundwater s les with 0.2 mM sulfate. In the suspended fraction of wells where the concentration of sulfate was between 0.03 and 0.2 mM, the archaeal community was dominated by sequences most closely related to the ANME-2D, a group of archaea known for anaerobically oxidizing methane. Based on available energy (∆G A ) estimations, results varied little for both sulfate reduction and methanogenesis throughout all wells studied, but could favor anaerobic oxidation of methane (AOM) in wells containing minimal sulfate and dihydrogen, suggesting AOM coupled with H 2 -oxidizing organisms such as sulfate or iron reducers could be an important pathway occurring in the Mahomet aquifer. Overall, the results show several distinct factors control the composition of microbial communities in the Mahomet aquifer. Bacteria that respire insoluble substrates such as iron oxides, i.e. Geobacter , comprise a greater abundance of the attached community than the suspended regardless of groundwater chemistry. Differences in community structure driven by the concentration of sulfate point to a clear link between the availability of substrate and the abundance of certain functional groups, particularly iron reducers, sulfate reducers, methanogens, and methanotrophs. Integrating both geochemical and microbiological observations suggest that the relationships between these functional groups could be driven in part by mutualism, especially between ferric-iron and sulfate reducers.
Publisher: American Geophysical Union (AGU)
Date: 09-2012
DOI: 10.1029/2011WR011568
Abstract: This study of the active bacteria residing in a pristine confined aquifer provides unexpected insights into the ecology of iron‐reducing and sulfate‐reducing bacteria in the subsurface. At 18 wells, we trapped the microbes that attached to aquifer sediment and used molecular techniques to examine the bacterial populations. We used multivariate statistics to compare the composition of bacterial communities among the wells with respect to the chemistry of the groundwater. We found groundwater at each well was considerably richer in ferrous iron than sulfide, indicating iron‐reducing bacteria should, by established criteria, dominate the sulfate reducers. Our results show, however, that areas where groundwater contains more than a negligible amount of sulfate ( .03 mM), populations related to sulfate reducers of the genera Desulfobacter and Desulfobulbus were of nearly equal abundance with putative iron reducers related to Geobacter , Geothrix , and Desulfuromonas. Whereas sulfate is a key discriminant of bacterial community structure, we observed no statistical relationship between the distribution of bacterial populations in this aquifer and the concentration of either ferrous iron or dissolved sulfide. These results call into question the validity of using the relative concentration of these two ions to predict the nature of bacterial activity in an aquifer. Sulfate reducers and iron reducers do not appear to be segregated into discrete zones in the aquifer, as would be predicted by the theory of competitive exclusion. Instead, we find the two groups coexist in the subsurface in what we suggest is a mutualistic relationship.
Location: United States of America
Location: United States of America
No related grants have been discovered for Theodore Flynn.