Several mutants of Rhizobium astragalus strain 107 with transposon Tn5 insertion fail to produce normal amount of extracellular polysaccharides, and induce on the host Astragalus sinicus L. only ineffective nodules void of the nitrogen-fixation activity.

• 紫云英根瘤菌菌株107经转座子Tn5诱变的胞外多糖合成缺陷型变种(Exo~-),在共生性状方面的改变有四种类型。