Diploid Heterozygous Hybrids From Matings Between Escherichia Coli and Salmonella Typhosa

Abstract

Sexuality in bacteria (1), now considered to be a unilateral conjugation (2, 3), has been studied in Escherichia coli b y m a n y workers. Luria and Burrous (4) have extended this form of genetic recombination to bacteria classified in different genera with their description of mating between E. coli and Shigella species. Recently, successful crosses between E. coli and Salmonella typhimurium were reported b y Baron eta/. (5). These studies dealt with the isolation of a streptomycin-resistant m u t a n t of S. typhimurium which acted as a high frequency recipient strain in matings with E. coli. Further studies b y Baron et al. (6) Materials and MethodsCultures.--The strains of S. typhosa employed were obtained from the culture collection at the Waiter Reed Army Institute of Research. A high frequency of recombination (Hfr) derivative of E. ¢otl K-12, strain W-1895, was obtained from Dr. P. D. Skaar, and a D-arabinose utilizing (v-Ara) mutant of this organism was isolated and employed in these studies.Media.--Meat extract agar, minimal media, EMB agar, and other culture media were used as described previously (5).Antisera.--Rabbit antisera were prepared against E. coU, S. typhosa, and selected hybrids by a series of intravenous injections of 109 viable or heat-killed (100°C. for 2 hours) cells. Absorbed sera were prepared as described by Edwards and Ewing (7).Phages.--The Vi typing phages were obtained from Dr. Cora Gunther; the procedures used for propagating these phages have been described by Baron et aL (8). The T series of bacteriophages were received from Dr. G. Bertani.Recombination Procedures.--For the detection of strains fertile with E. coli K-12, Hfr strain W-1895, the various cultures of S. typhosa which were to be tested as recipients (females) were spread with the E. coli culture as the donor (male) strain at a ratio of twenty recipient cells to one donor cell on an appropriate selective medium. The E. coli culture was grown in

Experimental Genetic Recombination in Vivo Between Escherichia Coli and Salmonella Typhimurium

“…These results support the premise that genetic recombination may have played a role in the evolution of the family Enterobacteriaceae. The data indicate also that hybrids recovered from in vivo matings are similar to those reported from in vitro crosses (3,4).…”

“…As was shown earlier, the hybrids appeared shortly after the S. typhimurium was introduced and increased rapidly indicating hybrid multiplication and making the determination of frequencies difficult. DISCUSSION The extensive studies of in dtro genetic recombination between E. coli and Shigella by Lurla and Burrous (1) and between E. coli and Salmonella by Baron et al (2)(3)(4) have demonstrated conclusively the interfertility existing between these organisms. Although the occurrence of organisms bearing characteristics of two established species may be the result of similar genetic mechanisms, the role of this phenomenon in nature has not been established.…”

Conservation and Transfer of Escherichia coli Genetic Segments by Partial Diploid Hfr Strains of Salmonella typhosa

“…From the results of this study, it is evident that a substantial amount of E. coli DNA can be conserved as a single, continuous, genetically complete segment in S. typhosa Hfr WR4000. The existence of continuous E. coli genetic segments of comparable lengths in some hybrids of S. typhosa WR4200 was inferred previously from segregation patterns (1)(2)(3), and from the results of DNA hybridization studies (9), but it has not been demonstrable. The demonstration of the presence of such diploid segments in S. typhosa Hfr WR4000 favors the notion that continuous E. coli DNA segments of this length can be maintained in S. typhosa WR4200.…”

“…In previous studies on the genetic hybridization of Salmonella typhosa strains with Escherichia coli Hfr donors, we observed the formation of heterozygous, partial diploid S. typhosa hybrids (1)(2)(3)(4)13). In these hybrids, the transferred E. coli genes usually persist without replacing the homologous S. typhosa alleles on the host chromosome.…”

“…Because only a part of the chromosomal material of the E. coli parent is conserved, the S. typhosa hybrid is diploid with regard to those of its genes which are matched by the inherited E. coil alleles, and haploid with respect to the remainder of its genome. This condition of the Salmonella hybrid is often an unstable one, and segregants which appear to have lost part or all of the E. coli deoxyribonucleic acid (DNA) may be obtained (1,3). The formation of partial diploid hybrids seems to be a common feature of intergeneric matings, having been observed also in crosses between E. coli and Shigella flexneri (10) and in matings between E. coli and Proteus mirabilis (11).…”