title: Impact of clay minerals on sulfate-reducing activity in aquifers.
abstract: Previous studies have shown that sulfate-reduction activity occurs in a heterogeneous manner throughout the terrestrial subsurface. Low-activity regions are often observed in the presence of clay minerals. Here we report that clays inhibit sulfate reduction activity in sediments and in a pure culture of Desulfovibrio vulgaris. Clay minerals including bentonite and kaolinite inhibited sulfate reduction by 70-90% in sediments. Intact clays and clay colloids or soluble components, capable of passing through a 0.2-microm filter, were also inhibitory to sulfate-reducing bacteria. Other adsorbent materials, including anion or cation exchangers and a zeolite, did not inhibit sulfate reduction in sediments, suggesting that the effect of clays was not due to their cation-exchange capacity. We observed a strong correlation between the Al2O3 content of clays and their relative ability to inhibit sulfate reduction in sediments (r2 = 0.82). This suggested that inhibition might be a direct effect of Al3+ (aq) on the bacteria. We then tested pure aluminum oxide (Al2O3) and showed it to act in a similar manner to clay. As dissolved aluminum is known to be toxic to a variety of organisms at low concentrations, our results suggest that the effects of clay on sulfate-reducing bacteria may be directly due to aluminum. Thus, our experiments provide an explanation for the lack of sulfate-reduction activity in clay-rich regions and presents a mechanism for the effect.
authors.affiliation: Department of Botany and Microbiology, Institute for Energy and the Environment, University of Oklahoma, Norman, OK 73019, USA.
authors.forename: D
authors.initials: D
authors.lastname: Wong
authors.forename: J M
authors.initials: JM
authors.lastname: Suflita
authors.forename: J P
authors.initials: JP
authors.lastname: McKinley
authors.forename: L R
authors.initials: LR
authors.lastname: Krumholz
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry / Q000633:toxicity; D001546:Bentonite / Q000737:chemistry* / Q000633:toxicity; D003901:Desulfovibrio / Q000378:metabolism* / Q000648:ultrastructure; D005618:Fresh Water; D019015:Geologic Sediments / Q000382:microbiology*; D007616:Kaolin / Q000737:chemistry* / Q000633:toxicity; D008855:Microscopy, Electron, Scanning; D009825:Oklahoma; D010084:Oxidation-Reduction / Q000187:drug effects*; D013431:Sulfates / Q000378:metabolism*
chemical_list: D013431:Sulfates; D001546:Bentonite; D007616:Kaolin; D000537:Aluminum Oxide