Evidence for the control of respiration by DNA in ultraviolet-irradiated Escherichia coli B-r cells

Role of Pyridine Nucleotides in the Control of Respiration in Ultraviolet-Irradiated Escherichia coli B/r Cells

Escherichia coli B/r cells grown on glycerol-containing medium and irradiated with ultraviolet light to about 1% survival respire for about 1 hr and then cease completely for several hours. The results of studies on cell-free respiration and analyses of pyridine nucleotide levels at various times after ultraviolet irradiation show that the cessation of respiration is associated with two changes-loss of glycerol kinase activity and complete disappearance of pyridine nucleotides. Under other cultural conditions in which respiratory inhibition is less complete and more transitory, the losses of pyridine nucleotides are smaller and the rises which follow are correlated with increases in respiratory activity.

Lack of UV-induced respiration shutoff in a recF strain of Escherichia coli: temperature conditional suppression at 30 degrees C by the sfrA mutation

A mutation in the recF gene of Escherichia coli results in a radiation-sensitive strain. The RecF pathway and the RecBC pathway account for nearly all of the conjugative recombination occurring in E. coli. recBC cells are radiation-sensitive and carry only out a small amount of recombination but these deficiencies are suppressed by an sbcB as recombination is shunted to the RecF pathway. A recBC sbcB recF strain is very radiation-sensitive and is devoid of recombination ability. These deficiencies are suppressed by the srfA mutation; srfA is a recA allele. UV-induced respiration shutoff is a recA+, lexA+ and recBC+ dependent. We report in this paper that respiration does not shutoff in a recF strain at 37 and 30 degrees C. an srfA mutation suppresses this lack of respiration shutoff effect in a recF srfA mutant at 30 degrees C but not at 37 degrees C; no suppression by this mutation occurs at either temperature in a recF recBC sbcB strain. An srfA strain also does not shut off its respiration at 37 degrees C and shows a temperature conditional UV-induced respiration shutoff response at 30 degrees C. The srfA mutation is thought to cause an altered RecA protein to be produced and we suggest that at 37 degrees This altered protein is temperature sensitive. We conclude from the results in this paper that the recF gene product is required for UV-induced respiration shutoff and that the RecA protein plays a special role in the induction process.

RecBC enzyme activity is required for far-UV induced respiration shutoff in Escherichia coli K12

Shutoff of respiration is one of a number of recA+ lexA+ dependent (SOS) responses caused by far ultraviolet (245 nm) radiation (UV) damage of DNA in Escherichia coli cells. Thus far no rec/lex response has been shown to require the recB recC gene product, the RecBC enzyme. We report in this paper that UV-induced respiration shutoff did not occur in either of these radiation-sensitive derivatives of K12 strain AB1157 nor in the recB recC double mutant. The sbcB gene product is exonuclease I and it has been reported that the triple mutant strain recB recC sbcB has near normal recombination efficiency and resistance to UV. The sbcB strain shut off its respiration after UV but the triple mutant did not show UV-induced respiration shutoff; the shutoff and death responses were uncoupled. We concluded that respiration shutoff requires RecBC enzyme activity. The RecBC enzyme has ATP-dependent double-strand exonuclease activity, helicase activity and several other activities. We tested a recBC+ (double dagger) mutant strain (recC 1010) that had normal recombination efficiency and resistance to UV but which possessed no ATP-dependent double-strand exonuclease activity. This strain did not shut off its respiration. The presence or absence of other RecBC enzyme activities in this mutant is not known. These results support the hypothesis that ATP-dependent double-strand exonuclease activity is necessary for UV-induced respiration shutoff.

Respiration shutoff in Escherichia coli K12 strains is induced by far ultraviolet radiations and by mitomycin C

Ultraviolet radiations (254 nm) (UV) cause respiration to shutoff in Escherichia coli B/r. It has been reported [P.A. Swenson, Photochem. Photobiol., 33 (1981) 855-859 and J. Barbé, A. Vericat and R. Guerrero, Mutation Res., 120 (1983) 1-5] that E. coli K12 strains do not shut off respiration after UV. The latter authors also reported that mitomycin C did not cause this 'SOS' response. In this paper we report that higher UV fluences than were previously used will cause respiration shutoff in K12 strain W3110 and that cyclic AMP increases the sensitivity of respiration shutoff of irradiated cell suspensions. We also report that mitomycin C shuts off respiration in this strain. Neither UV nor mitomycin C causes respiration shutoff in the recA56 derivative of W3110. Thus respiration shutoff is a recA dependent response to UV and mitomycin C in E. coli K12 strains.

Evolution of cellular ATP concentration after UV-mediated induction of SOS system in Escherichia coli

UV-irradiation of E. coli induces a two fold increase in ATP pool in the first 20 min. Afterwards, in RecA+ strains ATP level drops quickly below values of non irradiated cells. Mutants of E. coli defective in RecA protein or with either RecA protease activity deficient or protease resistant LexA repressor do not present this decrease, showing that it is due to cleavage of LexA repressor by RecA protease. The ATP increase produced in the first 20 min is dependent on RecBC exonuclease activity and it must be due to substrate level phosphorylation since an uncoupler such as dinitrophenol does not affect it.

DNA synthesis in Escherichia coli B/r after UV-irradiation

When studying the kinetics of DNA synthesis, growth and cell division in Escherichia coli B/r after irradiation with different doses of UV-radiation (254 nm) we could demonstrate, by means of pulse incorporation of 3H-thymidine, a lag in DNA synthesis after the irradiation. The relative rate of the restored DNA synthesis (related to the number of viable cells) was higher than in the non-irradiated culture. After 3 h the rate of DNA synthesis settled at a constant value, which was identical with the control rate up to the "critical dose" of 20 J/m2. The irradiated cell population is heterogenous and contains basically two categories of cells--surviving and non-surviving. Cells of both types contribute to DNA synthesis restored after the lag period to a different extent. During the first hour after the irradiation even the nonviable portion of the population, i.e. cells that do not form colonies but are still penicillin-sensitive, is involved in the DNA synthesis.

The muc+ gene of plasmid pKM101 prevents respiration shutoff in far ultraviolet-irradiated Salmonella typhimurium

The plasmid PKM101 is known to protect Escherichia coli and Salmonella typhimurium against killing by far UV irradiation and to enhance UV-induced mutagenesis. The muc+ gene of the plasmid is responsible for both of these effects. This paper shows that respiration of S. typhimurium shuts off about an hour after UV irradiation and that pKM101 prevents the shutoff. Plasmids which contained Tn5 translocatable elements, either in (and having produced a muc mutation) or flanking the muc+ gene, have been introduced into S. typhimurium. The muc mutant plasmid, which does not protect its host against UV killing and does not enhance UV induced mutagenesis, also does not protect against UV induced respiration shutoff. Likewise, plasmids in which the Tn5 translocatable elements flank the muc+ gene protect against shutoff of respiration. Thus the muc+ gene of pKM101 is responsible for protection against UV induced shutoff of respiration in S. typhimurium.

Role of cyclic adenosine 3',5'-monophosphate on cessation of respiration in ultraviolet-irradiated Escherichia coli

The addition of cyclic adenosine 3',5'-monophosphate (cAMP) to ultraviolet-irradiated Escherichia coli B/r cultures causes additional cells to cease respiring and to die. These effects of cAMP are greater on glucose-grown cells, where the effects of ultraviolet radiations alone are smaller and where the intracellular concentrations of cAMP are known to be lower.

Repair, replication and survival in uv-irradiated Escherichia coli

The influence of dimer removal through excision or photoreactivation on the kinetics of DNA synthesis, sedimentation profiles of DNA molecules and survival of cells was investigated in excision-deficient and excision-proficient Escherichia coli K-12 after a flux of 20 J M-2. In excision-deficient cells photoreactivation did not influence the kinetics of DNA synthesis for a long period and the sedimentation properties of DNA synthesized immediately after photoreactivation were influenced only slightly. However, survival was increased remarkably. In excision-proficient cells where dimers were removed through excision, the kinetics of DNA synthesis increased rapidly, normal-sized DNA molecules were synthesized 60 min after irradiation and survival was substantially higher than in the above-mentioned case. This can hardly be interpreted as a more complete repair of dimers by excision because the persistence of dimers in these cells did not significantly influence either the kinetics of DNA synthesis or normalization of DNA molecules and/or survival of cells. It is concluded that persisting dimers play an important role in excision-deficient but not in excision-proficient cells, that a non-dimer damage to DNA causes inhibition of DNA synthesis after UV and that this damage is of primary importance for excision-proficient cells which can easily cope with persisting dimers.

Delayed ultraviolet light-induced cessation of respiration by inadequate aeration of Escherichia coli

Inadequately aerated Escherichia coli B/r cultures did not shut their respiration off 60 min after ultraviolet light (52 M/m2 at 254 nm) as they did when well supplied with oxygen. Since cessation of respiaration is associated with cell death, the result suggested that oxygen toxicity by superoxide radicals generated by cell metabolism might be responsible for cell death. The specific activity of superoxide dismutase, which scavenges O2- radicals, increased twofold after 90 min of adequate aeration, but the specific activity of catalase remained constant. Respiration and viability of irradiated cells were affected not at all by the presence of superoxide dismutase and only slightly by the presence of catalase. Metal ions such as Mn2+ and Fe2+ inducers of superoxide dismutase, had no effect on respiration and viability. When irradiated cells were incubated under N2 for 90 min, the respiration, growth, and viability time-course responses were the same as for the cells not exposed to anareobiosis. We conclude that superoxide anions generated at the time of irradiation play no part in cessation delays the ultraviolet light-induced synthesis of proteins responsible for the irreversible cessation of respiration.

Pyrimidine dimer excision in surviving and nonsurviving cells of ultraviolet-irradiated cultures of Escherichia coli

We compared dimer excision in viable and nonviable cells fractions separated from Escherichia coli B/r cultures exposed to ultraviolet (UV) irradiation. For cells grown on minimal medium with glycerol as a carbon source, both fractions from the irradiated (20 J/m2, 5% survival) culture excised 60 to 70% of the thymine dimers from prelabeled DNA within 120 min. This percentage was, within experimental error, the same as that obtained from unseparated cultures. When isolated viable and nonviable populations were given a second UV exposure (20 J/m2) both types of cells were again able to excise dimers. The UV survival curve for the isolated viable population indicates that these cells are no more sensitive to radiation than exponentially growing cells not previously exposed to UV. The extent of dimer excision after UV irradiation was also the same in viable and nonviable cells separated from cultures grown on a glucose minimal medium in which both populations excised about 85% of the dimers within 120 min. These results show that the extent of removal of pyrimidine dimer from deoxyribonucleic acid is not precisely correlated with survival of repair-competent bacterial cells after exposure to UV light.

Centrifugal separation of irradiated cultures of Escherichia coli cells into viable and nonviable populations

Incubation of ultraviolet-irradiated Escherichia coli B/r cultures with 0.7% Triton X-100 resulted in a large decrease in turbidity. Under phase-contrast optics, most of the irradiated detergent-treated cells were smaller than normal and of low phase density; only a small percentage were normal or larger than normal and of normal phase density. Irradiated cells not treated with detergent showed fewer pronounced morphological changes. Irradiated cells treated with detergent lost large amounts of proteins and ribonucleic acid, but not of deoxyribonucleic acid. Such cultures could be separated by centrifugation into populations of (i) slowly sedimenting cells consisting of small, phase-light cells of low viability and (ii) large cells of normal phase density and high viability (100%). A similar separation was effected in gamma-irradiated cultures.

Evidence relating cessation of respiration, cell envelope changes, and death in ultraviolet-irradiated Escherichia coli B-r cells

Ionic and nonionic detergents have little effect on respiring bacteria, but in cultures poisoned with KCN rapid solubilization of the cell membrane, as indicated by turbidity losses, takes place. Ultraviolet radiations cause Escherichia coli cells grown in minimal medium with glycerol as a carbon source to cease respiring and growing about 1 h after irradiation. We tested the effect of the nonionic detergent Triton X-100 on growth and cell membrane dissolution (both measured by turbidity changes), respiration, and viability of unirradiated and irradiated E. coli B/r cells. When the detergent was added to cells immediately after irradiation, a decrease in turbidity occurred only when respiration was about to cease; when it was added after cessation of respiration, the turbidity loss was immediate. In both cases the turbidity loss was about 60%, and disintegration of the cell walls did not take place. 5-Fluorouracil (FU) and thermal (42 C) treatments cause respiration of irradiated cells to be maintained and also cause viability increases. Irradiated cells treated with FU and detergent show no turbidity loss just prior to the time respiration normally ceases, but a loss does occur in irradiated cells incubated with detergent at 42 C. We conclude that FU maintains respiration for all of the cells, but that thermal treatment maintains respiration for only part of the cells. In all cases the detergent had only a negligible effect on the respiration and viability of unirradiated and irradiated cells. We conclude that Triton X-100 causes solubilization of cell membranes of only nonrespiring cells that are not destined to survive.

Death through respiratory failure of a fraction of ultraviolet-irradiated Escherichia coli b-r cells

Escherichia coli B/r cells grown on a glycerol-containing medium and ultraviolet (UV)-irradiated to about 0.5% survival respire for about 1 hr and then cease for several hours. The cells that have completed repair and recovery processes begin to divide about 120 min after UV treatment, but this division is completely inhibited in liquid medium by caffeine, which delays repair of the irradiated deoxyribonucleic acid (DNA). When 5-fluorouracil (FU) is used to maintain respiration, the number of cells which form colonies when plated increases about 60-fold within 1 hr after irradiation. At least part of this increase does not involve repair while the cells are in the liquid medium because when caffeine is present there is still a 20-fold increase in colony formation. We conclude that many irradiated cells, although capable of carrying out complete and accurate repair of their DNA, die of respiratory failure; only when continuance of respiration is favored by FU treatment is their colony-forming potential realized. After an early increase, the number of cells able to form colonies in medium that contains FU remains constant while the completion of repair and recovery occurs. After these processes are completed, the number of cells able to form colonies increases slowly, except in the presence of caffeine, presumably because the late increase requires that repair steps take place while the cells are in liquid medium prior to cell division.

Release of the -galactosidase-synthesizing system from ultraviolet catabolite repression by cyclic 3',5'-adenosine monophosphate, dark repair, photoreactivation, and cold treatment

Recovery from the inhibitory effect of ultraviolet irradiation on the induced synthesis of beta-galactosidase was studied in Escherichia coli B/r. When irradiated cells (520 ergs/mm(2) at 254 nm) were induced and incubated in minimal medium supplemented with Casamino Acids (conditions of catabolite repression), the ability to form enzyme was greatly reduced for about 100 min and then recovery began. The inhibition observed immediately after ultraviolet irradiation was partially reversed by cyclic 3',5'-adenosine monophosphate (cyclic AMP) or by photoreactivation treatment. Inhibition was reduced if the cells were given cold treatment (5 C) before or during irradiation; the kinetics of induced enzyme formation in each case were similar to those of irradiated cells receiving cyclic AMP. These kinetics suggest that the cold treatments, like cyclic AMP, cause the release of the beta-galactosidase-synthesizing system from catabolite repression. When irradiated cells were incubated for various times before cyclic AMP or photoreactivation treatment, some reversal of the inhibition of induced enzyme formation was obtained, but by 100 min the treatments were ineffective. Because 100 min was also the time at which dark recovery of enzyme formation began, the recovery process was interpreted to be the result of completion of DNA repair, which, in turn, released the beta-galactosidase-synthesizing system from catabolite repression.

Role of pyridine nucleotides in 5-fluorouracil-mediated reactivation of ultraviolet radiation damage

Ultraviolet irradiation (520 ergs/mm(2) at 254 nm) causes the respiration of Escherichia coli B/r cells to cease after about 90 min postirradiation incubation in a minimal medium containing glycerol as the sole source of carbon. The cessation of respiration is associated with loss of pyridine nucleotides. Agents which interfere with postirradiation transcription and translation prevent cessation of respiration. We have studied the effects of one of these agents, 5-fluorouracil (FU), on respiration, pyridine nucleotide levels, viability, capacity to support phage growth, and the repair of irradiated deoxyribonucleic acid (DNA). Addition of FU to cells immediately after irradiation results in the continuance of respiration at a linear rate and the maintenance of high levels of pyridine nucleotides. Cellular viability increases dramatically during the first 60 min of postirradiation incubation in the presence of FU. The ability of irradiated cells to support the growth of phage T4 is also greatly increased. FU treatment has no effect on the kinetics of pyrimidine dimer excision or the degradation of DNA. However, treated cells repair single-strand breaks resulting from early steps in excision repair slightly more efficiently than do untreated cells. The results support the hypothesis that one of the causes of death in these irradiated cells is the disappearance of pyridine nucleotides, coenzymes of certain respiratory dehydrogenases, and, in the case of nicotinamide adenine dinucleotide, for polynucleotide ligase, the enzyme responsible for the final step in the repair of DNA.