Conservation of Salmonella typhimurium deoxyribonucleic acid by chromosomal insertion in a partially diploid Escherichia coli hybrid.

A partially diploid Escherichia coli hybrid recovered from mating with a Salmonella typhimurium donor was converted to an Hfr strain, designated WR2080, as a means to examine the manner in which the added Salmonella genetic material was conserved in it. The Salmonella argH-+, metB-+, and RHA-+ alleles contained as supernumerary genes in WR2080 were transferred together to E. coli recipients in interrupted mating experiments approximately 25 min after initial parental contact; transfer of the allelic E. coli genes by a haploid Hfr of the same transfer orientation occurred between 23.5 min (argH-+) and 25 min (rha-+) after initial contact. Entry of the E. coli ilv-+ marker of WR2080 in these experiments occurred at 29.5 min, 1.5 min later than the entry time of this marker from the haploid E. coli Hfr. When unselected inheritance of the recessive E. coli argH-minus and rha-minus alleles of WR2080 was examined among ilv-+ selected E. coli recipients in which unselected inheritance of the Salmonella donor genes was shown to be low (8%), inheritance of argH-minus was only 7%, whereas 51% inherited the neighboring rha-minus gene. In a comparative cross employing a haploid E. coli Hfr, in which rha inheritance was similar at 56%, argH inheritance was 41%. It was concluded that the Salmonella genes contained in WR2080 were conserved on a genetic segment about 1.5 min in length chromosomally inserted near the allelic E. coli genes, thus creating a duplication on that region within the hybrid chromosome.