Comparison of Humic Substance- and Fe(III)-Reducing Microbial Communities in Anoxic Aquifers

Abstract

Humic substances can mediate electron transfer between microorganisms and Fe(III) minerals. Because it is unknown which microorganisms reduce humics in anoxic aquifers, we analyzed the diversity and physiological flexibility of Fe(III)-, humics-, and AQDS-reducers, which were present at up to 10⁶ cells g⁻¹. No significant differences in 16S rRNA gene based diversity were found between enrichment cultures reducing ferrihydrite, humics or AQDS. Even after repeated transfers many of the enrichments retained the ability to switch to other electron acceptors. This suggests that humics- and Fe(III)-reducing microorganisms in anoxic aquifers are rather versatile and able to reduce different extracellular electron acceptors.

Keywords:

• DGGE
• electron shuttling
• Fe(III) reduction
• humic acids

Acknowledgments

We would like to thank Dr. Anwar Zahid for providing Araihazar aquifer samples and Dr. Hans-Hermann Richnow and Dr. Petra Bombach for providing Weißandt-Gölzau aquifer samples and the geochemical data from the site. The institutions of Arcadis Deutschland GmbH (office Freiberg, Saxony), the Landesanstalt für Altlastenfreistellung (Magdeburg, Saxony-Anhalt), and the Mitteldeutsche Sanierungs- und Entsorgungsgesellschaft (Bitterfeld, Saxony-Anhalt) are especially acknowledged for providing access and logistical support to the investigated site and for organizing the sampling and drilling campaigns. Thanks to Karin Stögerer for DGGE and help with qPCR.

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Additional information

Funding

Financial support came from Arcadis Deutschland GmbH (office Freiberg, Saxony), the Landesanstalt für Altlastenfreistellung (Magdeburg, Saxony-Anhalt), and the Mitteldeutsche Sanierungs- und Entsorgungsgesellschaft (Bitterfeld, Saxony-Anhalt). Also, this research was funded by the German Research Foundation (DFG), research unit FOR 580 “Electron Transfer Processes in Anoxic Aquifers.”