SUMMARY: Various toxic and non-toxic strains can be grouped according to DNA binding homology but not according to DNA composition. The guanine + cytosine (GC) contents of DNA from six strains were 28 to 30%. DNA binding with radioactive DNA from type E, MINN strain, revealed that the non-proteolytic strains type B, 17, type F, 202 and type E, DETROIT are 100% homologous to the E, MINN strain. type E, 32, the boticin producing s 5, and the non-toxic 24 NT, 26 NT and 5 i had 58 to 78% homology with the MINN strain. type A, 62 and 78, type B, 32, type C, 573, and non-toxic OS/E1, OS/E7 and OS/MINN strains had only 6 to 14% homology with type E, MINN. Competition experiments with unlabelled DNA confirmed these results. The studies indicate that strains which are closely related serologically and biochemically are also closely related genetically, and The data do not support the idea of a common origin of the non-toxic os strains and type E. The toxic type E strains and the toxic type A, B and C strains of are genetically heterogenous.


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