Recombinant clone heterogeneity in Escherichia coli conjunction: effect of pH and partially replicated recipient deoxyribonucleic acid.

At pH 6.8, a substantial fraction of recombinant colonies obtained from conjugation with an HfrH donor contained multiple recombinant classes in a single colony (polygenotype colony). In contrast, when the conjugation was performed at pH 7.6, the number of polygenotypic colonies was drastically reduced, and the recombinant colonies were predominantly monogenotypic or digenotypic. Genetic analysis revealed that the digenotypic recombinants differ in those donor markers near the origin of DNA replication but share those donor markers near the terminus. This integration pattern suggests that the formation of digenotypic recombinants involves recombination of a single copy of the exogenome with a partially replicated recipient DNA molecule. This suggestion was supported by examination of the genotype of recombinant colonies recovered from crosses with an HfrKL96 donor which was derived from HfrH but transfers its chromosome in the reverse direction.