Occurrence of hopanoid lipids in anaerobic Geobacter species

Authors

  • Thomas Härtner,

    1. Institut für Mikrobiologie, Mikrobiologie/Biotechnologie, Universität Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany
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  • Kristina L. Straub,

    1. Fakultät für Biologie, Universität Konstanz, Postfach 5560, D-78457 Konstanz, Germany
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  • Elmar Kannenberg

    Corresponding author
    1. Institut für Mikrobiologie, Mikrobiologie/Biotechnologie, Universität Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany
    2. Complex Carbohydrate Research Center, The University of Georgia, Athens, GA, 30602-4712, USA
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  • Edited by K. Hantke

*Corresponding author. Tel.: +1 706 542 2949; fax: +1 706 542 4412, E-mail address: elmark@ccrc.uga.edu, elmar.kannenberg@uni-tuebingen.de

Abstract

Geobacter metallireducens and G. sulfurreducens have been classified as strictly anaerobic bacteria which grow and thrive in subsurface and sediment environments. Hopanoids are pentacyclic triterpenoid lipids and are important for bacterial membrane stability and functioning. Hopanoids predominantly occur in aerobically growing bacteria of oxic environments. They rarely have been found in facultatively anaerobic bacteria and, to date, not at all in strict anaerobes. Our research shows that anaerobically grown G. metallireducens and G. sulfurreducens bacteria contain a range of hopanoid lipids, such as diploptene (i.e. hop-22(29)-ene) and hop-21-ene, and more complex, elongated hopanoids. In geological formations, diagenetic derivatives of hopanoids are widely used as biomarkers and are recognized as molecular fossils of bacterial origin. To date, these biomarkers have largely been interpreted as those derived from ancient oxic environments. Our findings presented here suggest that this interpretation needs to be re-evaluated. In addition to the origin in oxic environments, ‘geohopanoids’ may originate from ancient anaerobic environments as well.

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