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Mutational Analysis of the Cell Surface and Nodulation Competitiveness of Rhizobium Leguminosarum Biovar Phaseoli
註釋The use of Rhizobium inoculants for legumes is restricted by the poor nodulation competitiveness of many inoculant strains. In soil with high indiginous populations of bacteria that can nodulate a given host, the inoculant strains may be found in few or none of the nodules. This presents a problem when the indigenous strains fix little or no nitrogen and therefore do not provide a benefit to host. A strain of Rhizobium is a successful competitor when its representation in the nodules is greater than its representation in the inoculum. To determine whetherthe surface plays a role in nodulation competitiveness of Rhizobium leguminosarum bv.phaseoli (Rlp), I performed an extensive search and analysis of transposon-insertion mutants with altered cell surfaces derived from two nonisogenic parental strains of Rlp, KIM5s and CE3. I isolated and characterized one mutant of CE3, designated CE3003, with a domed colony morphology and a highly hydrophobic cell surface. On bean plants CE3003 was as efficient as CE3 in nodulation and acetylene reduction. The parent and the mutant grew at similar rates when they were each grown in rich culture medium or when inoculated singly onto bean seeds. However, when they were mixed at a 1:1 ratio and applied to seeds, the population of the mutant was 14-fold lower than the population of CE3 on bean roots five days after inoculation. CE3003 was significantly less competitive than CE3. A 16,860-fold excess of the mutant in mixed inocula was required to obtain equal nodule occupancy by ...