Dowling D N, Samrey U, Stanley J, Broughton W J
J Bacteriol. 1987 Mar;169(3):1345-8. doi: 10.1128/jb.169.3.1345-1348.1987.
One type of competitive interaction among rhizobia is that between nonnodulating and nodulating strains of Rhizobium leguminosarum on primitive pea genotypes. Pisum sativum cv. Afghanistan nodulates effectively with R. leguminosarum TOM, and this can be blocked in mixed inoculations by R. leguminosarum PF2, which does not nodulate this cultivar. We termed this PF2 phenotype Cnb+, for competitive nodulation blocking. Strain PF2 contains three large plasmids including a 250-kilobase-pair symbiotic (Sym) plasmid. Transfer of this plasmid, pSymPF2, to nonblocking rhizobia conferred the Cnb+ phenotype on recipients in mixed inoculations on cultivar Afghanistan with TOM. A library of the PF2 genome constructed in the vector pMMB33 was used to isolate two cosmid clones which hybridize to pSymPF2. These cosmids, pDD50 and pDD58, overlapped to the extent of 23 kilobase pairs and conferred a Cnb+ phenotype on recipient Cnb- rhizobia, as did pSD1, a subclone from the common region.
根瘤菌之间的一种竞争相互作用是豆科根瘤菌的非结瘤菌株和结瘤菌株在原始豌豆基因型上的相互作用。豌豆品种阿富汗能与豆科根瘤菌TOM有效结瘤，而在混合接种时，这种结瘤会被不能使该品种结瘤的豆科根瘤菌PF2阻断。我们将PF2的这种表型称为Cnb +，即竞争性结瘤阻断。菌株PF2含有三个大质粒，包括一个250千碱基对的共生（Sym）质粒。将该质粒pSymPF2转移到非阻断性根瘤菌中，在与TOM混合接种于阿富汗品种时，赋予受体Cnb +表型。利用在载体pMMB33中构建的PF2基因组文库分离出两个与pSymPF2杂交的黏粒克隆。这些黏粒pDD50和pDD58重叠了23千碱基对的范围，并赋予受体Cnb -根瘤菌Cnb +表型，来自共同区域的亚克隆pSD1也是如此。
