Burkardt B, Schillik D, Pühler A
Plasmid. 1987 Jan;17(1):13-25. doi: 10.1016/0147-619x(87)90004-7.
Intact megaplasmids of Rhizobium meliloti 2011 have been isolated and visualized by electron microscopy. The contour lengths of 64 megaplasmid molecules were determined. One definite class of molecules of 400 micron length and a range of larger molecules with lengths of up to 560 micron was observed. The contour lengths of the megaplasmids pRme2011a and pRme2011b were measured after isolation from plasmid-free Agrobacterium strains into which they had been individually transferred. Plasmid pRme2011a corresponds to the 400-micron class of megaplasmids while plasmid pRme2011b belongs to the 560-micron class. Preparatively isolated megaplasmids pRme2011a and b showed completely different restriction patterns. The pattern of total megaplasmid DNA from R. meliloti 2011 is composed of those from pRme2011a and b, suggesting that no more than two different megaplasmids exist. Because the length distributions of measured molecules were broad, R. meliloti 2011 megaplasmids seem to vary in length in vivo. Because only pRme2011a hybridized with a nifHD probe, this is the Sym plasmid. For R. meliloti strain MVII-1, which carries the megaplasmids pRmeMVII-1f and pRmeMVII-1g, pRmeMVII-1f was shown to be the Sym plasmid. Buoyant density determinations of R. meliloti 2011 and MVII-1 megaplasmids gave a value of 1.717 g/cm3 for pSym, which is that of Agrobacterium DNA. The buoyant density of the second megaplasmid was 1.721 g/cm3, corresponding to the density of the R. meliloti chromosome. As determined by reassociation kinetics, pRme2011a and b are unrelated. The degree of relatedness between strains MVII-1 and 2011 was 82%.
苜蓿中华根瘤菌2011完整的大质粒已通过电子显微镜分离并观察到。测定了64个大质粒分子的轮廓长度。观察到一类长度为400微米的确定分子以及一系列长度达560微米的更大分子。从分别转入无质粒农杆菌菌株后分离得到的大质粒pRme2011a和pRme2011b的轮廓长度进行了测量。质粒pRme2011a对应于400微米类的大质粒，而质粒pRme2011b属于560微米类。制备性分离的大质粒pRme2011a和b显示出完全不同的限制性酶切图谱。苜蓿中华根瘤菌2011总大质粒DNA的图谱由来自pRme2011a和b的图谱组成，表明存在不超过两种不同的大质粒。由于所测分子的长度分布较宽，苜蓿中华根瘤菌2011大质粒在体内长度似乎存在差异。因为只有pRme2011a与nifHD探针杂交，所以这是共生质粒。对于携带大质粒pRmeMVII - 1f和pRmeMVII - 1g的苜蓿中华根瘤菌菌株MVII - 1，pRmeMVII - 1f被证明是共生质粒。苜蓿中华根瘤菌2011和MVII - 1大质粒的浮力密度测定得出共生质粒pSym的值为1.717 g/cm³，与农杆菌DNA的值相同。第二个大质粒的浮力密度为1.721 g/cm³，与苜蓿中华根瘤菌染色体的密度相对应。通过复性动力学测定，pRme2011a和b不相关。菌株MVII - 1和2011之间的相关性程度为82%。
