Martinez-Romero Esperanza, Rosenblueth Monica
Departamento de Genética Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Ap. P. 565-A, Cuernavaca, Morelos, Mexico.
Appl Environ Microbiol. 1990 Aug;56(8):2384-2388. doi: 10.1128/aem.56.8.2384-2388.1990.
Rhizobium leguminosarum bv. phaseoli strain collections harbor heterogeneous groups of bacteria in which two main types of strains may be distinguished, differing both in the symbiotic plasmid and in the chromosome. We have analyzed under laboratory conditions the competitive abilities of the different types of Rhizobium strains capable of nodulating Phaseolus vulgaris L. bean. R. leguminosarum bv. phaseoli type I strains (characterized by nif gene reiterations and a narrow host range) are more competitive than type II strains (that have a broad host range), and both types are more competitive than the promiscuous rhizobia isolated from other tropical legumes able to nodulate beans. Type I strains become even more competitive by the transfer of a non-Sym, 225-kilobase plasmid from type II strain CFN299. This plasmid has been previously shown to enhance the nodulation and nitrogen fixation capabilities of Agrobacterium tumefaciens transconjugants carrying the Sym plasmid of strain CFN299. Other type I R. leguminosarum bv. phaseoli transconjugants carrying two symbiotic plasmids (type I and type II) have been constructed. These strains have a diminished competitive ability. The increase of competitiveness obtained in some transconjugants seems to be a transient property.
菜豆根瘤菌菜豆生物型菌株库中包含不同种类的细菌，其中可区分出两种主要类型的菌株，它们在共生质粒和染色体方面均存在差异。我们在实验室条件下分析了能够使菜豆（Phaseolus vulgaris L.）结瘤的不同类型根瘤菌菌株的竞争能力。菜豆根瘤菌菜豆生物型I型菌株（以nif基因重复和宿主范围狭窄为特征）比II型菌株（宿主范围广泛）更具竞争力，并且这两种类型的菌株都比从其他能够使菜豆结瘤的热带豆科植物中分离出的混杂根瘤菌更具竞争力。通过从II型菌株CFN299转移一个非共生的225千碱基质粒，I型菌株的竞争力变得更强。先前已证明该质粒可增强携带CFN299菌株共生质粒的根癌农杆菌转接合子的结瘤和固氮能力。还构建了其他携带两个共生质粒（I型和II型）的菜豆根瘤菌菜豆生物型I型转接合子。这些菌株的竞争能力有所减弱。在一些转接合子中获得的竞争力增强似乎是一种短暂的特性。
