Molecular and General Genetics MGG

, Volume 241, Issue 5–6, pp 602–615 | Cite as

Identification of a new class of nitrogen fixation genes in Rhodobacter capsalatus: a putative membrane complex involved in electron transport to nitrogenase

  • Manfred Schmehl
  • Andreas Jahn
  • Andreas Meyer zu Vilsendorf
  • Silke Hennecke
  • Bernd Masepohl
  • Markus Schuppler
  • Martin Marxer
  • Jürgen Oelze
  • Werner Klipp
Original Articles


DNA sequence analysis of a 12236 by fragment, which is located upstream of nifE in Rhodobacter capsulatus nif region A, revealed the presence of ten open reading frames. With the exception of fdxC and fdxN, which encode a plant-type and a bacterial-type ferredoxin, the deduced products of these coding regions exhibited no significant homology to known proteins. Analysis of defined insertion and deletion mutants demonstrated that six of these genes were required for nitrogen fixation. Therefore, we propose to call these genes rnfA, rnfB, rnfC, rnfD, rnfE and rnfF (for Rhodobacter nitrogen fixation). Secondary structure predictions suggested that the rnf genes encode four potential membrane proteins and two putative iron-sulphur proteins, which contain cysteine motifs (C-X2-C-X2-C-X3-C-P) typical for [4Fe-4S] proteins. Comparison of the in vivo and in vitro nitrogenase activities of fdxN and rnf mutants suggested that the products encoded by these genes are involved in electron transport to nitrogenase. In addition, these mutants were shown to contain significantly reduced amounts of nitrogenase. The hypothesis that this new class of nitrogen fixation genes encodes components of an electron transfer system to nitrogenase was corroborated by analysing the effect of metronidazole. Both the fdxN and rnf mutants had higher growth yields in the presence of metronidazole than the wild type, suggesting that these mutants contained lower amounts of reduced ferredoxins.

Key words

Rhodobacter capsulatus rnf genes In vivo and in vitro nitrogenase activities Iron-sulphur proteins Ferredoxins Metronidazole 


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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Manfred Schmehl
    • 1
  • Andreas Jahn
    • 2
  • Andreas Meyer zu Vilsendorf
    • 1
  • Silke Hennecke
    • 1
  • Bernd Masepohl
    • 1
  • Markus Schuppler
    • 1
  • Martin Marxer
    • 2
  • Jürgen Oelze
    • 2
  • Werner Klipp
    • 1
  1. 1.Lehrstuhl für Genetik, Fakultät für BiologieUniversität BielefeldBielefeldGermany
  2. 2.Institut für Biologie II der Universität FreiburgFreiburg i.Br.Germany

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