Ferruginous (Fe-rich, SO4-poor) conditions are generally restricted to freshwater sediments on Earth today, but were likely widespread during the Archean and Proterozoic Eons. Lake Towuti, Indonesia, is a large ferruginous lake that likely hosts geochemical processes analogous to those that operated in the ferruginous Archean ocean. The metabolic potential of microbial communities and related biogeochemical cycling under such conditions remain largely unknown. We combined geochemical measurements (pore water chemistry, sulfate reduction rates) with metagenomics to link metabolic potential with geochemical processes in the upper 50 cm of sediment. Microbial diversity and quantities of genes for dissimilatory sulfate reduction (dsrAB) and methanogenesis (mcrA) decrease with increasing depth, as do rates of potential sulfate reduction. The presence of taxa affiliated with known iron- and sulfate-reducers implies potential use of ferric iron and sulfate as electron acceptors. Pore-water concentrations of acetate imply active production through fermentation. Fermentation likely provides substrates for respiration with iron and sulfate as electron donors and for methanogens that were detected throughout the core. The presence of ANME-1 16S and mcrA genes suggests potential for anaerobic methane oxidation. Overall our data suggest that microbial community metabolism in anoxic ferruginous sediments support coupled Fe, S and C biogeochemical cycling.
Bibliographical noteFunding Information:
This study was financially and logistically supported by the ICDP priority program of the Deutsche Forschungsge-meinschaft (DFG Schwerpunktprogramm) through grants to Jens Kallmeyer (KA 2293/8-1), Aurèle Vuillemin (VU 94/1-1) and William Orsi (OR 417/1-1); the Swiss National Science Foundation (SNSF grant no. P2GEP2_148621 to Aurèle Vuillemin); the Helmholtz Center Potsdam, German Research Center for Geoscience (GFZ); and an NSERC Discovery grant (no. 0487) to Sean A. Crowe.
© 2018 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.
Copyright 2018 Elsevier B.V., All rights reserved.
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