Characterization of Lethal Zygosis Associated with Conjugation in Escherichia coli K-12

Abstract

When F − cells are mixed with an excess of Hfr cells there is a lethal event which results in a decrease in the number of F − survivors. We have described and discussed the parameters affecting this phenomenon of lethal zygosis, and these include the cultural conditions of both donor and recipient cells prior to mixing and the use of aeration throughout the period of the experiment. The absence of lethal zygosis with filtrates and supernatant fluids from donors suggests a dependence on direct cell-cell contact as found in conjugation. The phenomenon, which is normally observed in liquid media, also occurs on solid media, and use of these two methods has allowed examination of strains of different mating types. Whereas most Hfr strains capable of producing normal yields of recombinants showed killing activity, no F + and only one F′ donor produced lethal zygosis. Only F − strains were sensitive to this phenomenon. The relationship between lethal zygosis and the various stages of conjugation is discussed.

Con − Mutants: Class of Mutants in Escherichia coli K-12 Lacking a Major Cell Wall Protein and Defective in Conjugation and Adsorption of a Bacteriophage

“…Media. Nutrient broth, nutrient agar, and minimal agar (supplemented with glucose and growth factors as required for recombinant selection) were as previously described (34,35). Eosin-methylene blue agar (Difco-0511) was supplemented with galactose (0.5%, wt/vol) or lactose (1%, wt/vol).…”

“…The derivatives of strain JC6256 carrying Col V2, ColVBTrp, R100-1, R136i-, R1-19, R386, and R538-ldrd (12, 49) were kindly provided by N. Willetts. Preparation of bacterial cultures. Bacterial cultures (usually in nutrient broth) were prepared as previously described (34,36). All cultures were incubated at 37 C.…”

Identification, characterization and benefits of an exclusion system in an integrative and conjugative element of Bacillus subtilis

“…Till now, experimental evidence demonstrating the selective advantages of exclusion has come from the characterization of lethal zygosis in the F plasmid (Skurray and Reeves, 1973;1974;Skurray et al, 1976;Ou, 1980). Recipients lacking the F plasmid (F-) are killed when mixed with an excess of Hfr or F+ exclusion-null donors.…”

dnaB gene of Escherichia coli K-12 affects superinfection inhibition between F' plasmids

“…In both instances, the donor-to-recipient ratio was 10:1 and conjugation was at 30 C for 60 min. Preliminary tests indicated that under these condi-tions lethal zygosis did not occur (32). From each mating experiment several hundred transconjugant colonies were scored.…”