HR: 10:50h
AN: B22D-03 INVITED    [Abstracts]
TI: Constraining the role of anoxygenic phototrophic Fe(II)-oxidizing bacteria in deposition of BIFs
AU: * Kappler, A
EM: andreas.kappler@uni-tubingen.de
AF: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, Tuebingen, 72076, Germany
AU: Posth, N R
AF: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, Tuebingen, 72076, Germany
AU: Hegler, F
AF: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, Tuebingen, 72076, Germany
AU: Wartha, E
AF: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, Tuebingen, 72076, Germany
AU: Huelin, S
AF: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, Tuebingen, 72076, Germany
AB: Banded Iron Formations (BIFs) are Precambrian sedimentary deposits of alternating iron oxide and silica mineral layers. Their presence in the rock record ca.3.8-2.2 Ga makes them particularly intriguing formations for the debate over when oxygen became dominant on Earth. The mechanism(s) of BIF deposition is still unclear; suggestions including both abiotic and biotic processes. We are interested in constraining one of these proposed mechanisms; the direct biological oxidation of Fe(II) via anoxygenic Fe(II)-oxidizing autophototrophs. In order to find the limitations of photoferrotrophic BIF deposition, we take a holistic approach, investigating the oxidation of Fe(II) by modern Fe(II)-oxidizing phototrophs, the precipitation of Fe(III) (hydr)oxides, and the fate of the cell-mineral aggregates in the water column and at the basin floor. Specifically, physiology experiments with Fe(II)-oxidizing phototrophs under various conditions of light intensity, pH, Fe(II) concentration and temperature allow us to determine the environmental limits of such organisms. We carry out precipitation experiments to characterize the sedimentation rates, aggregate size and composition in order to resolve the effect of reactions in the water column. Finally, we simulate the diagenetic fate of these aggregates on the basin floor by placing them in gold capsules under T and P conditions relevant for the Transvaal Supergroup BIFs of South Africa. Recently, we have developed a tank simulating the Archean ocean in which the strains grow in continuous culture and collect the aggregates formed under various geochemical conditions. We aim to model the extent of and limitations to photoferrotrophs in BIF deposition. This information will help constrain whether biotic processes were dominant in the Archean ocean and will offer insight to the evolution of the early biogeosphere.
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting