DNA synthesis in a synchronized culture ofEscherichia coli 15 TAUbar after continuous and interrupted thymine starvation

After transfer to a thymine-containing medium the DNA synthesis did not increase with increasing intervals of thymine starvation. On the other hand, the starvation interrupted at regular intervals by 5 min thymine pulses resulted in an increased DNA synthesis. Induction of a bacteriophage which is prevented by the pulses is discussed as a possible reason for the observed difference in kinetics of the DNA synthesis following continuous and interrupted thymine starvation. Turbidity of the culture increased roughly three times, both during the continuous and the interrupted thymine starvation. The increase of the turbidity after prolonged interrupted starvation was lower than that which would correspond to the observed increase of the DNA synthesis according to the hypothesis of a critical mass of the cell resulting in the initiation (Donachie, 1968).     

The effect of bacteriophage induction on the repair ability ofEscherichia coli 15 TAU

The growth, lysis and survival ofEscherichia coli 15 TAU following UV irradiation was examined. An attempt was made to separate the repair processes and prophage induction by preincubation with chloramphenicol and subsequent incubation with chloramphenicol or caffeine. It was found that the prophage induction does not diminish the repair ability of cells that have survived the induction. It cannot be ascertained whether the cell fraction was induced at all or whether the induction was partially reverted subsequently. It can be concluded that the results derived from examining the survival of tially reverted subsequently. It can be concluded that the results derived from examining the survival of UV-irradiation cultures ofEscherichia coli 15 TAI do not require any correction for phage induction.     

Growth and cell division ofEscherichia coli 15 TAU after transfer to deficient media with different sources of carbon and energy

We studied growth and cell division ofEscherichia coli 15 TAU after transfer to thymine-free medium with different sources of carbon and energy or to the same medium in which not only thymine but also arginine and/or uracil were omitted. After transfer to thymine-free medium only a fraction of cells divides once. The size of the dividing fraction is predetermined particularly by conditions of balanced growth before inhibition of DNA synthesis and only slightly affected by conditions after transfer, while the growth rate after shift to medium with different source of carbon and energy changes abruptly. Following transfer to arginine-deficient media cell division proceeds much more slowly than in other cases tested. The fraction of cells which causes a deviation of rate maintenance after shift-up and shift-down (Cooper, 1969) seems to be the same as the cell fraction dividing after transfer to thymine-free medium.     

Phases of thymineless death inEscherichia coli 15 TAU

On the basis of the course of loss of colony-forming ability it was possible to disting guish at least three phases of thymineless death in a culture ofEscherichia coli 15 TAU starved in a thymine-free medium enriched with arginine and uracil. The main differences between the individual phases were: (a) half-time of the loss of colony-forming ability; (b) only in the first phase was thymineless death reversible; (c) beginning in the second phase, part of the cells lysed after thymine was added to the liquid medium or when cells were plated on agar with complete medium; (d) lysis was much slower in the third phase than in the second; (e) in the presence of caffeine the course of the first and second phase was not affected but cells did not die in the third phase. Cells surviving in the third phase in the presence of caffeine are probably those which did not die even in medium T^?A^?U^? (Maaløe & Hanawalt, 1961). Transition from one phase to another was caused neither by change in the composition of medium during thymine starvation nor by heterogeneity of this culture from a genetical point of view.     

Metabolism of glycerol-3-phosphate and phospholipids in a temperature-sensitive lysis mutant ofEscherichia coli

Phospholipid metabolism in a temperature-sensitive lysis mutant ofEscherichia coli has been investigated. The incorporation of³²P into the phospholipids of this mutant was negligible, not only at the non-permissive temperature, as was demonstrated earlier, but also at 30 C. Furthermore, cultivation of the cells at the non-permissive temperature during 90 min, which is the time required to induce lysis, did not alter the amount of phospholipid per cell.In vitro experiments demonstrated that the enzymes involved in phospholipid biosynthesis are fully active at 42 C. Lysis therefore is not directly caused by a defect in phospholipid synthesis. Evidence is presented that the low³²P incorporation is the result of a defective glycerol-3-phosphate dehydrogenase which determines the turnover of the immediate lipid precursor, glycerol-3-phosphate.     

Effect of thymine starvation on messenger ribonucleic acid synthesis in Escherichia coli

Luzzati, Denise (Institut de Biologie Physico-Chimique, Paris, France). Effect of thymine starvation on messenger ribonucleic acid synthesis in Escherichia coli. J. Bacteriol. 92:1435-1446. 1966.-During the course of thymine starvation, the rate of synthesis of messenger ribonucleic acid (mRNA, the rapidly labeled fraction of the RNA which decays in the presence of dinitrophenol or which hybridizes with deoxyribonucleic acid) decreases exponentially, in parallel with the viability of the thymine-starved bacteria. The ability of cell-free extracts of starved bacteria to incorporate ribonucleoside triphosphates into RNA was determined; it was found to be inferior to that of extracts from control cells. The analysis of the properties of cell-free extracts of starved cells shows that their decreased RNA polymerase activity is the consequence of a modification of their deoxyribonucleic acid, the ability of which to serve as a template for RNA polymerase decreases during starvation.     

The broth effect and mutation frequency decline in cells ofEscherichia coli after irradiation with UV-light

Dependence of the broth effeot and the phenomenon of mutation frequency decline on dose of the applied UV radiation was investigated in the strainEscherichia coli B/r Hcr+ thy trp. Reversions to Trp⁺ were followed. The degree of the broth effect and the mutation frequency decline is minimal within the range of UV doses corresponding to a survival of cells lower than 10-1. In connection with the two effects, excision of thymine dimers, initiation of synthesis, synthesis and degradation of DNA were also investigated. It was found that stimulation or inhibition of an inaccurate postreplication repair mechanism, rather than inhibition or stimulation of excision of thymine dimers, are responsible for the broth effect and the mutation frequency decline, respectively.     

The effect of thymine starvation on chromosomal structure of Escherichia coli JG-151

Labelled DNA extracted from control and thymine starved cells was qualitatively characterized with respect to sedimentation properties in alkaline sucrose gradients. DNA isolated from cells undergoing loss of division ability demonstrated decreasing sedimentation velocity. Sedimentation profiles of DNA extracted from cells which were starved for thymine under conditions which allowed spontaneous recovery of division ability to occur, demonstrated an increase in DNA sedimentation velocity toward normal control value. It appears that while thymine starvation can result in single strand breaks, this damage is not irreversible, for under certain conditions rejoining of the breaks can occur.     

The influence of thymine and 5-bromouracil on the sensitivity ofEscherichia coli to alkylation,UV and X-irradiation

The influence is followed of an alkylating agent (triethylene-melamine) UV and X-irradiation on the survival ofEscherichia coli 15 T∋ells grown in a minimal medium containing enzymatic hydrolysate of caseine. Thymine-less death of a considerable number of cells was observed in a culture grown in this medium. A conclusive difference in the sensitivity to the lethal agents used was found between a culture grown in a thymine-less medium and bacteria grown in a medium containing excess (20 μg/ml) of thymine. The culture grown with a sufficient thymine concentration was more sensitive to alkylation and X-rays, whereas bacteria surviving conditions of thymine-less death were more resistant to the above agents. However, such cells were more sensitive to UV-irradiation. The differences found are discussed from the point of view of DNA concentrations found in the individual cultures.     

A proteolytic system in growing and non-growing cells ofEscherichia coli

1. (1)
   Escherichia титр клетки содер жат протеазы Система разделения собственных белков в качестве равно как казеин с символикой (вс131) Я на несколько ще лочного рН. Темпы про теолиза не заметно влияют ethylenediaminotetraacetic кислоту или iodoacetic кисло та, п-chlormercuribenzoate снижает темп ы гидролиза (su131) Я казеи н, но ее эффект не може т быть отменено цист еина.     
   
   

Survival ofEscherichia coli after storage in various frozen menstrua

The effect of storage at –9 C onEscherichia coli was examined. In buffer or water, survival after three days was less than 40%. Dimethylsulfoxide (DMSO) (10%) and glycerol (10%) were very protective with over 90% survivors. Variability of replicate samples was greater with frozen than with non-frozen suspensions.With a slide culture technique, it was found that the time required for the thawed cells to complete their first division was increased up to a time equivalent to over two divisions, dependent upon the protective storage menstrua.Injury as shown by inability to grow on a minimal medium after thawing was negligible when the cells were frozen in DMSO or glycerol. Cells stored in frozen buffer were sensitive to a 20 min treatment with actinomycin D following thawing but cells frozen in glycerol or DMSO showed little death or injury. The results suggest that an alteration of the cell envelope is initially responsible for death by freezing.This work was supported in part by U.S. Public Health Service Research Grant EF-428 from the Division of Environmental Engineering and Food Protection.