Gene clusters involved in anaerobic benzoate degradation of Geobacter metallireducens

Authors

  • Simon Wischgoll,

    1. Institute for Biology II, Microbiology, University of Freiburg, 79104 Freiburg, Germany.
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    • Both authors contributed equally to this manuscript.

  • Dimitri Heintz,

    1. Laboratoire de Spéctrometrie de Masse Bio-Organique, CNRS, ECPM, Université Louis Pasteur de Strasbourg, France.
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    • Both authors contributed equally to this manuscript.

  • Franziska Peters,

    1. Institute for Biology II, Microbiology, University of Freiburg, 79104 Freiburg, Germany.
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  • Anika Erxleben,

    1. Institute for Biology II, Plant Biotechnology, University of Freiburg, 79104 Freiburg, Germany.
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  • Eric Sarnighausen,

    1. Institute for Biology II, Plant Biotechnology, University of Freiburg, 79104 Freiburg, Germany.
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  • Ralf Reski,

    1. Institute for Biology II, Plant Biotechnology, University of Freiburg, 79104 Freiburg, Germany.
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  • Alain Van Dorsselaer,

    1. Laboratoire de Spéctrometrie de Masse Bio-Organique, CNRS, ECPM, Université Louis Pasteur de Strasbourg, France.
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  • Matthias Boll

    Corresponding author
    1. Institute for Biology II, Microbiology, University of Freiburg, 79104 Freiburg, Germany.
      E-mail boll@biologie.uni-freiburg.de; Tel. (+49) 761 203 2685; Fax (+49) 761 203 2626.
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    • Dedicated to Professor Georg Fuchs, Freiburg on the occasion of his 60th birthday.


E-mail boll@biologie.uni-freiburg.de; Tel. (+49) 761 203 2685; Fax (+49) 761 203 2626.

Summary

The degradation of aromatic compounds follows different biochemical principles in aerobic and anaerobic microorganisms. While aerobes dearomatize and cleave the aromatic ring by oxygenases, facultative anaerobes utilize an ATP-dependent ring reductase for the dearomatization of the activated key intermediate benzoyl-coenzyme A (CoA). In this work, the aromatic metabolism was studied in the obligately anaerobic model organism Geobacter metallireducens. The gene coding for a putative carboxylic acid-CoA ligase was heterologously overexpressed and the gene product was characterized as a highly specific benzoate-CoA ligase catalysing the initial step of benzoate metabolism. However, no evidence for the presence of an ATP-dependent benzoyl-CoA reductase as observed in facultative anaerobes was obtained. In a proteomic approach benzoate-induced proteins were identified; the corresponding genes are organized in two clusters comprising 44 genes. Induction of representative genes during growth on benzoate was confirmed by reverse transcription polymerase chain reaction. The results obtained suggest that benzoate is activated to benzoyl-CoA, which is then reductively dearomatized to cyclohexa-1,5-diene-1-carbonyl-CoA, followed by β-oxidation reactions to acetyl-CoA units, as in facultatively anaerobic bacteria. However, in G. metallireducens the process of reductive benzene ring dearomatization appears to be catalysed by a set of completely different protein components comprising putative molybdenum and selenocysteine containing enzymes.

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