Genetic hybridization of the leu-ilv region in bacilli

Two auxotrophic strains of Bacillus subtilis 168 served as recipients for DNA extracted from various wild-type strains of B. subtilis and wild-type species of the genus Bacillus. Depending upon the DNA source, heterologous transformations of the linked try-his-tyr loci were either as efficient as those observed with donor DNA obtained from the wild type B. subtilis 168 strain or were undetectable. The order and relative distances of the three gene loci were the same for all active DNA preparations. Similar results were obtained in heterologous transformations of the linked leu-ilv loci, except that DNA preparations from the Bacillus globigii and B. subtilis var. niger species exhibited a reduced but detectable frequency of transformation. With the latter preparations a marked polarity of integration favouring the leu+ gene was observed, an effect not seen with homologous DNA. Six independent hybrid lines were obtained from transformation of B. subtilis leu- ilv- with DNA from B. subtilis var. niger leu+ ilv+. DNA extracted from these lines fell into two classes on the basis of activity in transforming the parental recipient strain: (i) indistinguishable from homologous DNA, and (ii) intermediate between homologous DNA and DNA from the original donor strain. With either class, polarity of integration was no longer observed in the leu-ilv region. The intermediate type of hybrid demonstrates that at least some of the inefficiency of heterospecific transformation must be due to heterology in nucleotide sequence between the different species at the leu-ilv loci.