The cycHJKL genes of Rhizobium meliloti involved in cytochrome c biogenesis are required for "respiratory" nitrate reduction ex planta and for nitrogen fixation during symbiosis

Attila Kereszt, Krystyna Slaska-Kiss, Peter Putnoky, Zsofia Banfalvi, Adam Kondorosi

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

We report the genetic and biochemical analysis of Rhizobium meliloti mutants defective in symbiotic nitrogen fixation (Fix-) and "respiratory" nitrate reduction (Rnr-). The mutations were mapped close to the ade-1 and cys-46 chromosomal markers and the mutated locus proved to be identical to the previously described fix-14 locus. By directed Tn5 mutagenesis, a 4.5 kb segment of the chromosome was delimited in which all mutations resulted in Rnr- and Fix- phenotypes. Nucleotide sequence analysis of this region revealed the presence of four open reading frames coding for integral membrane and membrane-anchored proteins. Biochemical analysis of the mutants showed that the four proteins were necessary for the biogenesis of all cellular c-type cytochromes. In agreement with the nomenclature proposed for rhizobial genes involved in the formation of c-type cytochromes, the four genes were designated cycH, cycJ, cycK, and cycL, respectively. The predicted protein product of cycH exhibited a high degree of similarity to the Bradyrhizobium japonicum counterpart, while CycK and CycL shared more than 50% amino acid sequence identity with the Rhodobacter capsulatus Ccll and Cc12 proteins, respectively. cycJ encodes a novel membrane anchored protein of 150 amino acids. We suggest that this gene cluster codes for (parts of) a multi-subunit cytochrome c haem lyase. Moreover, our results indicate that in R. meliloti c-type cytochromes are required for respiratory nitrate reduction ex planta, as well as for symbiotic nitrogen fixation in root nodules.

Original languageEnglish
Pages (from-to)39-47
Number of pages9
JournalMGG Molecular & General Genetics
Volume247
Issue number1
DOIs
Publication statusPublished - Jan 1 1995

Keywords

  • Cytochrome c biogenesis
  • Rhizobium meliloti
  • Symbiotic nitrogen fixation "Respiratory" nitrate reductase
  • cyc genes

ASJC Scopus subject areas

  • Genetics

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