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      Humic substance-mediated Fe(III) reduction by a fermenting Bacillus strain from the alkaline gut of a humus-feeding scarab beetle larva.

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          Abstract

          Humus-feeding macroinvertebrates play an important role in the transformation of soil organic matter. Their diet contains significant amounts of redox-active components such as iron minerals and humic substances. In soil-feeding termites, acid-soluble Fe(III) and humic acids are almost completely reduced during gut passage. Here, we show that the reduction of Fe(III) and humic acids takes place also in the alkaline guts of scarab beetle larvae. Sterilized gut homogenates of Pachnoda ephippiata no longer converted Fe(III) to Fe(II), indicating an essential role of the gut microbiota in the process. From Fe(III)-reducing enrichment cultures inoculated with highly diluted gut homogenates, we isolated several facultatively anaerobic, alkali-tolerant bacteria that were closely related to metal-reducing isolates in the Bacillus thioparans group. Strain PeC11 showed a remarkable capacity for dissimilatory Fe(III) reduction, both at pH 7 and 10. Rates were strongly stimulated by the addition of the redox mediator 2,6-antraquinone disulfonate and by redox-active components in the fulvic-acid fraction of humus. Although the contribution of strain PeC11 to intestinal Fe(III) reduction in P. ephippiata remains to be further elucidated, our results corroborate the hypothesis that the lack of oxygen and the solubilization of humic substances in the extremely alkaline guts of humivorous soil fauna provide favorable conditions for the efficient reduction of Fe(III) and humic substances by a primarily fermentative microbiota.

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          Author and article information

          Journal
          Syst. Appl. Microbiol.
          Systematic and applied microbiology
          1618-0984
          0723-2020
          Jun 2012
          : 35
          : 4
          Affiliations
          [1 ] Mikrobielle Ökologie, Fachbereich Biologie, Universität Konstanz, 78457 Konstanz, Germany.
          Article
          S0723-2020(12)00045-8
          10.1016/j.syapm.2012.03.003
          22525666
          1b537d4f-902c-49c6-98a3-ab748672b05e
          Copyright © 2012 Elsevier GmbH. All rights reserved.
          History

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