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Archives of Microbiology

, Volume 165, Issue 5, pp 297–305 | Cite as

The Bradyrhizobium japonicum fixGHIS genes are required for the formation of the high-affinity cbb3-type cytochrome oxidase

  • O. Preisig
  • Rachel Zufferey
  • H. Hennecke
Original paper

Abstract

We report structural and functional analyses of the Bradyrhizobium japonicum fixGHIS genes, which map immediately downstream of the fixNOQP operon for the symbiotically essential cbb 3-type heme-copper oxidase complex. Expression of fixGHIS, like that of fixNOQP, is strongly induced in cells grown microaerobically or anaerobically. A fixGHI deletion led to the same prominent phenotypes as those known from a fixNOQP deletion: defective symbiotic nitrogen fixation (Fix) and decreased cytochrome oxidase activity in cells grown under oxygen deprivation. Only traces, if any, of cytochrome cbb 3 subunits were present in membranes isolated from the ΔfixGHI strain, as revealed by Western blot analysis with subunit-specific antibodies. This effect was not due to lack of fixNOQP transcription. The results suggested a critical involvement of the fixGHIS gene products in the assembly and/or stability of the cbb 3-type heme-copper oxidase. On the basis of sequence similarities between the FixI protein and a Cu-transporting P-type ATPase (CopA) of Enterococcus hirae, and between FixG and a membrane-bound oxidoreductase (RdxA) of Rhodobacter sphaeroides, we postulate that a membrane-bound FixGHIS complex might play a role in uptake and metabolism of copper required for the cbb 3-type heme-copper oxidase.

Key words Cytochrome oxidase Ion transport Membrane protein assembly P-type ATPase Symbiotic nitrogen fixation 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1996

Authors and Affiliations

  • O. Preisig
    • 1
  • Rachel Zufferey
    • 1
  • H. Hennecke
    • 1
  1. 1.Mikrobiologisches Institut, Eidgenössische Technische Hochschule, ETH-Zentrum, Schmelzbergstrasse 7, CH-8092 Zürich, Switzerland Tel. +41-1-632-3318; Fax +41-1-632-1148 e-mail: hennecke@micro.biol.ethz.chCH

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