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根瘤菌Ｓ２５从海南岛山毛豆分离得到，在分类上比较独特。该菌株具有较强抗逆性，如耐酸、耐亚硝酸、对多种抗生素具有抗性。质粒检测结果显示，它含有一条大约１５０ｋｂ的大质粒。以共同结瘤基因ｎｏｄＡＢＣ和固氮酶结构基因ｎｉｆＨＤＫ为探针与质粒进行分子杂交，结果表明，该质粒载有结瘤与固氮基因（即为共生质粒）。用带有蔗糖敏感基因的Ｔｎ５Ｂ１２转座子进行质粒消除，通过含蔗糖的ＴＹ平板正向筛选获得质粒缺失突变株。与野生型亲本菌株相比，质粒丢失菌株不能结瘤固氮，该质粒缺失菌株的抗酸性显著降低，亚硝酸耐受性减弱，多种抗生素抗性丢失；同时该质粒也涉及到菌株的多种碳源和氮源代谢。以无质粒农杆菌为媒介，质粒回复能使菌株恢复到野生型性状。
Rhizobium S25 isolated from the Hainan Island soybean, more unique in the classification. The strain has strong resistance, such as acid, nitrite-resistant, resistant to a variety of antibiotics. The plasmid test results show that it contains a large plasmid of about 150kb. The molecular hybridization of nodABC and nifHDK, a common nodulation gene and plasmid, showed that the plasmid contained nodulation and nitrogen fixation genes (ie, a symbiotic plasmid). Plasmids were removed using the Tn5B12 transposon with sucrose-sensitive genes, and plasmid deletion mutants were obtained by positive selection with sucrose-containing TY plates. Compared with the wild-type parental strains, the plasmid-lost strains could not nodulate and fix nitrogen. The strains lacking the acid-resistance of the strains were significantly reduced, the nitrite tolerance was weakened and the resistance of multiple antibiotics was lost. At the same time, the plasmid also involved many strains Carbon and nitrogen sources. With plasmid-free Agrobacterium-mediated transformation of the plasmid can restore the strain to the wild-type trait.