紫云英根瘤菌共生基因分布及其共生效应的多样性

从同一植株不同根瘤分离40株紫云英根瘤菌，所有菌株对10种抗生素的抗药性测定表明，该群体分为22个抗药类群，质粒检测显示所有公离株都含有质粒，质粒数1～4条，用快生型大豆根瘤菌USDA205质粒作参考，估测质粒Mr分布范围为83～226MU．根据图谱分析表明，该菌群可分为6个不同质粒型．各类型质粒通过与Dig-nodABC和Dig-nifHDK杂交，结果显示带有1条质粒的菌株其共生基因定位在染色体上．带有2条或2条以上质粒的菌株各拥有1条共生质粒，共生质粒Mr范围有差异，大约为117～220MU．研究结果也显示，不同质粒型的菌株其共生效应存在明显差异，其中第6质粒型的菌株共生固氮率最强，第1质粒型菌株共生固氮率较低．共生固氮能力最强的第6质粒型菌株，只占总菌数7．5％．

DIVERSITY OF SYMBIOTIC GENE LOCATION AND SYMBIOTIC EFFECTIVENESS OF RHIZOBIUM HUAMIII STRAINS

Forty strains of Rhizobium huakuii were isolated from different nodules on the same heat plant (1 isolate from 1 nodule). Intrinsic antibiotic resistance (IAR) of all strains was tested with 10 antibiotics and they could be classified into 22 IAR clusters. The plasmid profiles of all strains were examined by using a mobified Eckhard procedure of plasmid visualization. The number of the strains varied from 1 to 4, and their M, were estimated at 83 to 226 Mu in comparison with the plasmids of strain USDA205 as reference. The plasmid profiles of all strains could be classified in to 6 different plasmid types by plasmid number and weight. All the plasmids were hybridized with nod ABC and nif HDK and the results showed that the symbiotic genes were located on Chromosome in the strain with one plasmid, and the strains with other plasmid types harbored one sym plasmid besides other plasmid(s). The Mr of the sym plasmids varied from 117 to 226 Mu. Symbiotic effectiveness of typical strains with different plasmid type was determined and the results indicated that their symbiotic effectiveness varied considerably. The symbiotic effectiveness of the strain with one plasmid was the lowest. The symbiotic effectiveness of the strains of the sixth plasmid type was the highest, but the numberof the strains was only a small portion in all the strains tested (7. 5% ).