Differences in the genetic structure of Bacillus subitilis strains carrying the trpE26 mutation and strain 168

Abstract

It was previously shown that in strains of B. subtilis bearing the trpE26 mutation, a chromosome segment (from trpD to ilvA) is translocated to a position near the thr region. Further PBS1-mediated transduction data now revealed that these strains also possess an inversion of part of the chromosome from the origin of replication, down to the tre locus on 1 side and the cysB locus on the other. These data concern evidence of linkage of tre-12 to markers in the translocation (hisH2, tyrA1 and metB3) and linkage of the cysB3 marker to thi-86, gly-133 and catA. They explain the previously observed absence of linkage of markers in the translocated segment to cysB3. The model proposed for the formation of merodiploids in trpE26 strains, which calls for the fusion of 2 genetic elements, is not incompatible with this new finding. The model was of more general significance. Merodiploids may also be produced from 168 recipients and trpE26 donors by transduction, when selection is made for particular markers. The markers should be in the ilvA and thr regions. They are widely separated in the recipient 168 strain but are closely linked in the trpE26 donor as a result of the translocation. The diploids so produced are unstable, sensitive to L-lysine, and segregate rapidly.