The cytochrome bc1 complex but not CycM is necessary for symbiotic nitrogen fixation by Rhizobium leguminosarum

Microbiology
G WuJ A Downie

Abstract

Following Tn5 mutagenesis of Rhizobium leguminosarum biovar viciae, two mutants in one complementation group were identified as being unable to fix nitrogen in pea nodules. Spectroscopic analysis revealed that the mutants had lowered levels of c-type cytochromes and cytochromes aa3, but increased levels of cytochrome d. Cells of the mutants were greatly reduced in their ability to oxidize the artificial electron donor N,N,N',N'-tetramethyl-p-phenylenediamine but membranes prepared from them had increased levels of succinate- and NADH-dependent respiration. NADH oxidation by the mutants was insensitive to the respiratory inhibitor antimycin A, that targets the cytochrome bc1 complex. Molecular analysis of the mutants revealed that they were affected in the cytochrome bc1 complex. One of the mutants contained Tn5 in a gene homologous to that encoding cytochrome c1, and in the other the Tn5 was in DNA homologous to that encoding the cytochrome b component of the cytochrome bc1 complex. Haem staining revealed that haem proteins of M(r)31,000 and M(r)23,000 were absent from membranes from the mutants whereas an additional soluble c-type cytochrome protein of M(r)23,000 was present. We conclude that the larger of these two haem prote...Continue Reading

Citations

Jun 6, 2003·Molecular Microbiology·Stefania MeloniJosé M Palacios
Sep 18, 1997·Microbiology and Molecular Biology Reviews : MMBR·L Thöny-Meyer

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