Bechet M, Guillaume J B
Can J Microbiol. 1978 Aug;24(8):960-6.
Seven effective (nitrogen-fixing) strains of Rhizobium meliloti have been studied. By sedimentation analysis of their alkaline lysates in alkaline sucrose gradients, a plasmid was found in four strains. In a strain (2011 str 3) which gave no result with this method, supercoiled DNA was detected by CsCl-dye buoyant density gradient centrifugation. That result was confirmed by analytical Cs2SO4-Ag+ density gradients, which showed a heterogeneity in the average base composition of the DNA extracted from three strains, including the 2011 str 3 strain. Two of those last strains seemed to contain an extrachromosomal DNA of very high molecular weight.
已对七株有效的（固氮）苜蓿根瘤菌菌株进行了研究。通过在碱性蔗糖梯度中对其碱性裂解物进行沉降分析，在四株菌株中发现了一种质粒。在一种用此方法未得到结果的菌株（2011 str 3）中，通过氯化铯-染料浮力密度梯度离心法检测到了超螺旋DNA。该结果通过分析性硫酸铯-银离子密度梯度得以证实，该梯度显示从包括2011 str 3菌株在内的三株菌株中提取的DNA的平均碱基组成存在异质性。最后这三株菌株中的两株似乎含有非常高分子量的染色体外DNA。
