A series of colicin-tolerant (tol) mutants of Escherichia coli K-12, which adsorbed colicins but were not killed by them, were isolated and studied genetically and physiologically. Three major classes of mutants were found: tol II, tolerant to colicins A, El, E2, E3, and K; tol III, tolerant to A, E2, E3, and K; and tol VIII, tolerant to El only. The sites of tol HI and tol III mutations mapped near the gal region (gene order: tol-gal-bio) and were cotransduced with gal by P1. In heterozygous diploids, tol+ was dominant over tol; tol II and tol III gave full comple-mLntation. All the tol mutations that mapped near gal rendered the bacteria more fragile during growth and hypersensitive to deoxycholate and to ethylenediaminetetraacetic acid. The tol VIII mutation mapped between str and his. These mutants were extremely sensitive to deoxycholate and were also hypersensitive to methylene blue, acridines, and various other compounds. The sensitivity is attributed to increased uptake due to selective alteration of the permeability barrier. The colicintolerant mutations are interpreted as affecting some components of the cytoplasmic membrane which mediate between the adsorbed colicin molecules and the target sites of their biochemical effects in the bacterial cell.

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A spontaneously arising regulatory mutant of the gluconate system in Escherichia coli was isolated. This mutant became constitutive, probably in one step, for gluconate high-affinity transport, gluconokinase, and gluconate-6-P dehydrase. The mutation involved ( gntR18 ) is cotransducible with asd . Pseudorevertants, derived from a mutant (M2) that shows a long lag for growth on gluconate mineral medium, were also isolated and characterized. They give constitutive levels of gluconokinase and gluconate-6-P dehydrase but lack high-affinity transport function. Genetic experiments performed with one of these pseudorevertants (M4) indicate that it carries a secondary mutation in the gntR gene. The M4 phenotype is thus the result of the interaction of expression of a constitutive mutation ( gntR4 ) with the mutation of strain M2 ( gntM2 ).

SUMMARYThe state of colicinogenic factors E,, I and V (col E,, col I and col V ) in Escherichia coli K12 was studied. The analysis of the results of conjugation experiments involving different Hfr or F+ and F-strains shows that: (1) The frequency of transfer of these colicinogenic factors differs markedly: col V is transferred with maximum efficiency, col E, and col I , on the contrary, only at low frequency. The non-colicinogenic character of the donor parent is never transmitted to recombinants. ( 5 ) Zygotes that have received col V , transmit it to all daughter cells. All these results lead to the conclusion that colicinogenic factors E,, I and V are in an extrachromosomal state in F+ and Hfr bacteria. The same conclusion would apply to their state in F-bacteria, since the results with colicinogenic factor V seem to indicate that this factor replicates in this type of bacteria autonomously and at a faster rate than the chromosome.