Transduction of linked genetic characters of the host by bacteriophage P1

[This corrects the article on p. 493 in vol. 32.].

https://mmbr.asm.org/content/mmbr/32/4_Pt_2/493.full.pdf

Antibiotic inhibitors of the bacterial ribosome.

Mechanism of Streptomycin Action on Bacteria: A Unitary Hypothesis

SUMMARY: Analysis of a pair of Bacterium coli K-12 mutants which had ceased to show genetic recombination after storage, implicated mutant 58-161, which had previously behaved as a gene donor strain, as the infertile parent. Infertile 58-161 failed to display recombination when crossed with a gene acceptor strain (W-677) but was able to mate successfully with wild-type K-12 and prototrophic recombinant donor strains, i.e. it had become a gene acceptor. The terms ‘F+’ and ‘F -’ have been adopted (after Lederberg, Cavalli & Lederberg, 1952) to denote donor and acceptor strains respectively. Growth of either 58-161/F - or W-677/F - in mixed broth culture with 58-161/F + resulted in the conversion to F + of up to 75% of re-isolated colonies of the initially F - strain. F - strains converted to F + by strains of dissimilar genotype showed no phenotypic alteration and, therefore, were not recombinants. Washed, mixed cultures on minimal agar yielded an F + conversion rate of only 3.6%, while 100% recombinants were F + under the same conditions. The F + agent could be transmitted serially through F - strains and was not filterable. While F - x F - crosses were sterile, F + x F - crosses showed maximum fertility. F + x F + crosses were c. 10–20 times less productive than F + x F -. The F + agent had a determining effect on the phenotype of recombinants. Thus, when the F + F - relationship was reversed in F + x F - crosses between the same pair of mutants, almost all recombinants which did not show new patterns of unselected marker characters had the phenotype of the F - parent. Among recombinants from F + x F + crosses, the phenotypes of both parents were represented though not always equally. This effect of F + on the phenotype of segregants invalidates much of the evidence for genetic linkage in K-12. Reversal of F + potential in otherwise similar crosses also had a marked effect on the efficiency of prototroph formation on minimal agar supplemented with various growth factors required by one of the parent auxotrophs. A tentative theory of the mechanism of recombination is presented on the basis of this and previous work. This supposes that F + is a non-lytic infectious agent, harboured by F + cells and absent from F - cells, which becomes effectively associated with a part (or parts) of the chromosomes of a small proportion of the cells it inhabits. The F + agent thus acts as a gene carrier in the transfer of genetic material from F + to F - cells.

/pdf/observations-on-a-transmissible-agent-determining-sexual-3gxk4k5ib4.pdf

Observations on a transmissible agent determining sexual differentiation in Bacterium coli

for the quantitative study of spontaneous mutability and of the mutagenic action of various agents such as radiations and chemicals. The, older of the two methods deals with mutational changes from phage sensitivity to phage resistance, and the more recently developed one (Demerec, 1951; Bertani, 1951) with back-mutations from streptomycin dependence to nondependence. In both cases the mutants can be easily classified; very large numbers of bacteria may be tested; and slight increases in mutation rate can be easily detected. After the streptomycin method had been developed we undertook extensive tests of a number of chemicals for mutagenicity, using mainly this method because it is the simpler of the two.

Nyholm Mh

Papers

The inheritance of streptomycin resistance and dependence in crosses of Escherichia coli.