Department of Plant Pathology, University of California, Riverside California 92521.
Plant Physiol. 1987 Oct;85(2):335-42. doi: 10.1104/pp.85.2.335.
Rhizobium leguminosarum bv. trifolii T24 is ineffective in symbiotic nitrogen fixation, produces a potent antibiotic (referred to here as trifolitoxin) that is bacteriostatic to certain Rhizobium strains, and is very competitive for clover root nodulation (EA Schwinghamer, RP Belkengren 1968 Arch Mikrobiol 64: 130-145). The primary objective of this work was to demonstrate the roles of nodulation and trifolitoxin production in the expression of nodulation competitiveness by T24. Unlike wildtype T24, transposon mutants of T24 lacking trifolitoxin production were unable to decrease clover nodulation by an effective, trifolitoxin-sensitive strain of R. leguminosarum bv. trifolii. A non-nodulating transposon mutant of T24 prevented clover nodulation by a trifolitoxin-sensitive R. leguminosarum bv. trifolii when co-inoculated with a T24 mutant lacking trifolitoxin production. Neither mutant alone prevented nodulation by the trifolitoxin-sensitive strain. These results demonstrate that trifolitoxin production and nodulation are required for the expression of nodulation competitiveness by strain T24. A trifolitoxin-sensitive strain of R. meliloti did not nodulate alfalfa when co-inoculated with T24 and a trifolitoxin-resistant strain of R. meliloti. Thus, a trifolitoxin-producing strain was useful in regulating nodule occupancy on a legume host other than clover. Trifolitoxin production was constitutive in both minimal and enriched media. Trifolitoxin was found to inhibit the growth of 95% of all strains of R. leguminosarum bvs. trifolii, viceae, and phaseoli tested. Strains of all 13 biotypes of R. leguminosarum bv. trifolii were inhibited by trifolitoxin. Three strains of R. fredii were also inhibited. Strain T24 ineffectively nodulated 46 clover species, did not nodulate Trifolium ambiguum, and induced partially effective nodules on Trifolium micranthum. Since T24 produced partially effective nodules on T. micranthum and since a trifolitoxin-minus mutant of T24 induced ineffective nodules, trifolitoxin production is not the cause of the symbiotic ineffectiveness of T24.
根瘤菌属三叶草变种 T24 在共生固氮方面无效，会产生一种强效抗生素（这里称为三叶草毒素），对某些根瘤菌菌株具有抑菌作用，并且对三叶草的根瘤形成具有很强的竞争力（EA Schwinghamer，RP Belkengren 1968 Arch Mikrobiol 64：130-145）。这项工作的主要目的是证明结瘤和三叶草毒素产生在 T24 表达结瘤竞争力中的作用。与野生型 T24 不同，缺乏三叶草毒素产生的 T24 转座子突变体无法通过有效的、对三叶草毒素敏感的根瘤菌属三叶草变种 T24 菌株降低三叶草的结瘤。当与缺乏三叶草毒素产生的 T24 突变体共同接种时，T24 的非结瘤转座子突变体阻止了三叶草毒素敏感的根瘤菌属三叶草变种 T24 的三叶草结瘤。单独的突变体都不会阻止三叶草毒素敏感菌株的结瘤。这些结果表明，三叶草毒素产生和结瘤是 T24 菌株表达结瘤竞争力所必需的。当与 T24 和三叶草毒素抗性的根瘤菌属 meliloti 菌株共同接种时，三叶草毒素敏感的根瘤菌属 meliloti 菌株不会接种紫花苜蓿。因此，产生三叶草毒素的菌株可用于调节除三叶草以外的豆科宿主上的根瘤占有率。三叶草毒素的产生在最小和丰富的培养基中都是组成型的。发现三叶草毒素抑制了测试的所有 95%的根瘤菌属三叶草变种、 viciae 和 phaseoli 菌株的生长。三叶草毒素抑制了所有 13 种三叶草变种的根瘤菌属三叶草变种的菌株。三株弗雷德里希氏菌也被抑制。T24 无效地结瘤了 46 种三叶草物种，没有结瘤 Ambiguum 三叶草，并且在 Micranthum 三叶草上诱导了部分有效的根瘤。由于 T24 在 Micranthum 三叶草上产生了部分有效的根瘤，并且 T24 的三叶草毒素缺失突变体诱导了无效的根瘤，因此三叶草毒素的产生不是 T24 共生无效的原因。
