Competitiveness of a nif− Bradyrhizobium japonicum mutant against the wild-type strain |
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Authors: | Matthias Hahn Daniel Studer |
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Affiliation: | Mikrobiologisches Institut, Eidgenössische Technische Hochschule, ETH-Zentrum, CH-8092 Zürich, Switzerland |
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Abstract: | Abstract By mixed inoculation experiments, the competitive ability of a nifD ::Tn 5 mutant of Bradyrhizobium japonicum was compared to its effective, isogenic parent strain. When the strains were inoculated in a 1:1 ratio at high concentration, the mutant was found to colonize almost as many nodules as the wild type. Thus, lack of expression of a functional nitrogenase system does not severely reduce competitiveness. In such experiments the majority of the nodules (> 60%) were infected by both wild-type and mutant strains. From statistical analysis it was concluded that a mean number of 2–4 bacteria have successfully elicited one nodule under the described conditions. Visual and microscopic observations of sections from mixed infected nodules revealed separated sectors containing effective or ineffective bacteroids. |
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Keywords: | Rhizobium ecology nitrogen-fixation symbiosis electron microscopy |
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