Characterization of group B colicin-resistant mutants of Escherichia coli K-12: colicin resistance and the role of enterochelin

Nine classes of group B colicin-resistant mutants were examined to study the role of enterochelin in colicin resistance. Four of the mutants studied (cbt, exbC, exbB, and tonB) hypersecreted enterochelin. Enterochelin hypersecretion was apparently responsible for resistance of the exbC mutant to colicins G and H and for resistance of the exbB mutant to colicins G, H, Ia, Ib, S1, and V. All four mutants scored as colicin B tolerant, even in the absence of enterochelin synthesis. The mutants produced substantially increased amounts of two high-molecular-weight outer membrane polypeptides when grown under limiting iron conditions. The presence of these polypeptides was correlated with increased colicin B-neutralizing activity in the outer membrane preparations.

Cross-resistance between bacteriophages and colicins in Escherichia coli K-12

Cross-resistance between bacteriophages and colicins was studied using collections of bacteriophage- and colicin-resistant mutants of Escherichia coli K-12. No new examples were found of highly specific one-to-one cross-resistance of the type suggestive of common receptors. However, several groups of mutants showed tolerance to colicins and resistance to bacteriophages. Mutants known to be very defective in lipopolysaccharides composition were found to commonly show tolerance to certain colicins in addition to their bacteriophage resistance. Another group of mutants showed varying patterns of resistance to colicins E2, E3, K, L, A, S4, N, and X and bacteriophages E4, K2, K20, K21, K29, and H+. However, many bacteriophage-resistant mutants were fully colicin sensitive, and most colicin-resistant mutants were fully sensitive to bacteriophages.

Iron uptake in colicin B-resistant mutants of Escherichia coli K-12

Four classes of colicin B-resistant mutants of Escherichia coli K-12 were examined for defects in iron uptake. All four mutant classes (cbt, exbC, exbB, and tonB) were defective in the uptake of ferri-ennterochelin. The tonB mutant was also defective in citrate-, ferrichrome-, and rhodoturulic acid-mediated iron uptake. The defects in iron transport were reflected in increased sensitivity to iron chelators and to chromium and aluminium salts, and in hypersecretion of enterochelin. One of the mutants (cbt) was apparently defective in outer membrane ferri-enterochelin receptor activity. aroE derivatives (unable to synthesize enterochelin) of the four mutant classes and the parent strain produced increased amounts of two outer membranes polypeptides when grown under iron stress. These polypeptides are implicated in ferri-enterochelin receptor activity.

Recipient ability of bacteriophage-resistant mutants of Escherichia coli K-12

The ability of a wide range of bacteriophage-resistant mutants to act as recipients in conjugation with F'lac pro and R100-1 donors has been studied. A number of mutant types defective in recipient ability with F'lac pro, as well as mutants which were hyperrecptive with R100-1, have been detected.

Colicin tolerance and map location of conjugation-deficient mutants

Con minus mutants, conjugation-defective mutants of Escherichia coli K-12, have been shown to be tolerant to colicins K and L. They map at approximately 14 min on the genetic map. The significance of the colicin tolerance of conjugation-defective mutants is discussed.

Genetics of resistance to colicins in Escherichia coli K-12: cross-resistance among colicins of group B

This paper describes the isolation of mutants resistant to colicins of group B (i.e., colicins B, D, G, H, Ia, Ib, M, Q, S1, and V). The 145 mutants studied in detail can be divided into nine phentopyic classes, based on their colicin-resistance patterns. They include the previously isolated tonA, tonB exbB and cir mutants. Each of the different phenotypic classes of mutants has been partially characterized, and some approximately mapped. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis has revealed substantial changes in the composition of the outer membrane proteins of exbB and tonB mutants.

Genetics of resistance to colicins in Escherichia coli K-12: cross-resistance among colicins of group A

By using each of the available colicins, we have isolated a large number of colicin-resistant mutants. They included both receptor and tolerant mutants and each was screened for cross-resistance to all other colicins. On the basis of the cross-resistance of these mutants it was possible to place known colicins into two mutually exclusive groups, group A and group B. Mutants selected as resistant to colicins of group A may or may not be cross-resistant to other colicins of group A, BUT Are never resistant to colicins of group B. The reverse also applies. The mutants isolated as resistant to colicins of group A (A, E1, E2, E3, K, L, N, S4, and X) have been divided into 21 phenotypic classes on the basis of their colicin resistance patterns. These include most of the tolerant and receptor mutants previously isolated, some of which were previously shown to also have an increased sensitivity to certain antibiotics and detergents. Type strains from each of the phenotypic classes were therefore tested for sensitivity to a range of antibiotics, detergents, and surfactants that included all those previously used. With these new data, it has been possible to speculate informatively on the mode of action of the different colicins. We have confirmed the position of previously isolated mutations on the Escherichia coli K-12 genetic map, and located approximately the loci conferring colicin resistance in some of the newly isolated mutants.

Bacteriophage resistance in Escherichia coli K-12: general pattern of resistance

Resistant mutants were isolated to 42 virulent bacteriophages in one strain of Escherichia coli K-12 and tested for resistance or sensitivity to a set of 56 bacteriophages. Most of the mutants fell into 11 groups with respect to their resistance patterns. It was possible to classify the bacteriophages broadly, according to the variety of mutants that were resistant to them.

Plasmid specificity of the origin of transfer of sex factor F

The ability of F-like plasmids to promote transfer from the F origin of transfer was determined. Chromosome transfer was measured from plasmid derivatives of RecA(-) Hfr deletion strains which had lost all the F transfer genes but which in some cases retained, and in others had also lost, the origin sequence. ColV2 and ColVBtrp could initiate transfer from the F origin, but R100-1, R1-19, and R538-1 drd could not. These results can be correlated with the plasmid specificity of the traI components of the different plasmid transfer systems, supporting the hypothesis that the origin of transfer is the site of action of the traI product. Most F-like plasmids, including R1-19 and R538-1 drd, could transfer ColE1, consistent with previous findings that the (plasmid-specific) traI product is not necessary for ColE1 transfer by Flac; ColE1 transfer may be initiated by a ColE1-or host-determined product. R100-1 and R136fin(-) could not transfer ColE1 efficiently, apparently because of differences residing in their pilus-forming genes.

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

We describe a new class of mutants of Escherichia coli K-12 defective in conjugation (Con(-) mutants). They lack a major protein of the outer membrane and are defective as recipients with Hfr and F' donors and as recipients for several F-like R factors and Col factors. In the case of crosses with an Hfr donor, we have shown that the Con(-) recipient is defective in pair formation. The mutants are resistant to certain phages due to loss of receptor activity.

F factor-mediated immunity to lethal zygosis in Escherichia coli K-12

Recipient (F(-)) cells of Escherichia coli are sensitive to an excess of Hfr donor cells. This phenomenon of lethal zygosis is associated with conjugation and is observed as a continuous fall in F(-) viable cells during liquid mating, or as inhibition of F(-) growth on solid media. One class of survivors, which arose in the zones of inhibition on solid media, was no longer sensitive to lethal zygosis and exhibited the following properties: sensitivity to male-specific phage, donor ability, and surface exclusion. Since these characteristics were sensitive to acridine orange treatment, the strains carry an F factor extrachromosomally. They are, however, defective in some way since they retain sensitivity to female-specific phage. Temporary sensitivity to lethal zygosis in these and in standard F(+) strains can be induced by the formation of F(-) phenocopies. We have suggested that there is an immunity to lethal zygosis (Ilz(+)) associated with the F factor and discuss the results in terms of this hypothesis.

Physiology of Escherichia coli K-12 during conjugation: altered recipient cell functions associated with lethal zygosis

The number of viable F(-) cells decreases when Escherichia coli recipient cells are mixed with an excess of Hfr cells. Evidence is presented showing that lethal zygosis was accompanied by changes in the physiology of the recipient cells, including (i) inhibition of deoxyribonucleic acid synthesis, (ii) inhibition of beta-galactosidase induction, (iii) altered transport and accumulation of galactosides, and (iv) leakage of beta-galactosidase into the supernatant fluid. The results are discussed in terms of possible conjugation-associated changes that, at high Hfr to F(-) ratios, lead to lethal zygosis.

Characterization of lethal zygosis associated with conjugation in Escherichia coli K-12

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.

Mode of action of colicins of types E1, E2, E3, and K

The effect of colicins on deoxyribonucleic acid and protein synthesis, and also their effect on the ability of T4 phage to replicate in Escherichia coli K-12, were studied. Colicins of type K inhibited deoxyribonucleic acid synthesis, protein synthesis, and phage growth. Among colicins of type E, there was an absolute correlation between mode of action and subdivision into types E(1), E(2), and E(3).