MOLECULAR ANALYSIS OF Rhizobium meliloti GENES INVOLVED IN NODULATION

Aguilar, O. Mario; Müller, Peter; Grönger, P.; Pühler, Alfred

doi:10.1007/978-94-009-6923-0_318

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“…R. meliloti MA3, MA4, MA5, and MA6 formed nodules (Nod'), but failed to reduce acetylene (Fix-). TnS insertion 11 delayed nodulation by 1 week. The remaining TnS insertions resulted in Nod' Fix' phenotypes.…”

Section: Resultsmentioning

confidence: 99%

“…First, R. meliloti transconjugants were selected on TY medium supplemented with streptomycin, neomycin, and tetracycline (selection for integration of the whole plasmid by a single crossover). In a second step, 1 Physical and genetic map of a symbiotic region of R. meliloti 2011. The location of the analyzed region ( ) of the insert of plasmid pRmSL26 (Liii) with respect to the nifHDK operon is indicated.…”

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Characterization of a Rhizobium meliloti fixation gene (fixF) located near the common nodulation region

Aguilar¹,

Kapp²,

Pühler³

1985

J Bacteriol

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Rhizobium meliloti 2011 DNA from pRmSL26, a plasmid which is known to carry genes involved in the early stages of nodulation, was used to construct Tn5 mutations by site-directed TnS mutagenesis. TnS mutations located within an 8.7 kilobase EcoRI fragment defined two adjacent loci encoding functions for nodulation (nod) and symbiotic N2 fixation (fix). We investigated the organization and regulation of thefix locus and the characteristics of alfalfa nodules induced by these Fixmutants. By monitoring expression in Escherichia coli minicells, we determined that thefix locus encoded a 36-kilodalton polypeptide. The gene corresponding to this locus was designatedfixF. Morphological and ultrastructural studies of the ineffective nodules formed by R. melilotifixF mutants showed infected host cells similar to those of the wild type. The ineffective nodules were able to accumulate leghemoglobin, but at lower levels than those found in the wild-type nodules. Expression of the niJHDK operon was unaffected by TnS insertions in the fixF gene. Expression of the fixF gene was monitored in E. coli by using translational lacZ fusions. It was shown that transcription of thefixF gene in E. coli could be activated by Klebsiella pneumoniae nifA and the R. meliloti nifA-like regulatory gene products. Expression of thefixF gene was also studied in free-living and symbiotic R. meliloti cells. It was found that the fixF gene was transcribed in the symbiotic state. * Corresponding author. present evidence indicating that the fix locus contained a single gene, designated fixF. Finally, by constructing translational fusions between the fixF and E. coli lacZ genes, we have studied the expression of thefixF gene in E. coli and in free-living and bacteroid forms of R. meliloti.

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confidence: 99%

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confidence: 99%