Starvation-specific formation of a peripheral exopolysaccharide by a marine Pseudomonas sp., strain S9

The marine bacterium Pseudomonas sp. strain S9 produces exopolysaccharides (EPS) during both growth and total energy source and nutrient starvation. Transmission electron microscopy of immunogold-labeled cells demonstrated that the EPS is closely associated with the cell surface during growth (integral EPS), while both the integral form and a loosely associated extracellular (peripheral) form were observed during starvation. Formation and release of the latter rendered the starvation medium viscous. In addition, after 3 h of starvation in static conditions, less than 5% of the cells were motile, compared with 100% at the onset of starvation and approximately 80% subsequent to release of the peripheral EPS at 27 h of starvation. Inhibition of protein synthesis with chloramphenicol added before 3 h of starvation caused no increase in viscosity. However, addition of chloramphenicol at 3 h did not prevent the subsequent increase in viscosity displayed by S9 cells. The amount of integral EPS increased for both nontreated and chloramphenicol-treated S9 cells during the first hour of starvation, with a subsequent equal decrease. The chloramphenicol-treated cells, as well as cells of a transposon-generated mutant strain deficient in peripheral EPS formation, remained adhesive to a hydrophobic inanimate surface during the initial 5 h of starvation, whereas nontreated wild-type cells had progressively decreased adhesion capacity. During the initial 5 h of starvation, most of the nontreated cells but only a small fraction of the chloramphenicol-treated and mutant cells detached from the hydrophobic substratum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exoprotease Activity of Two Marine Bacteria during Starvation

Exoprotease activity during 120 h of total energy and nutrient starvation was examined in two marine bacteria, Vibrio sp. strain S14 and Pseudomonas sp. strain S9. The activity was determined by spectrophotometric measurement of the rate of release of soluble color from an insoluble azure dye derivative of hide powder (hide powder azure). Starved cells of both strains (5 h for S14, and 4 or 24 h for S9) showed greater extracellular proteolytic activity than at the onset of starvation. The exoprotease activity of cells starved for longer periods of time then decreased, but was found to be present at significant levels throughout the starvation period studied (120 h). The accumulation of exoprotease activity in the bulk phase during starvation indicated that both strains constitutively excreted extracellular proteases. As deduced from experiments with chloramphenicol, de novo protein synthesis during starvation was required for the production and/or release of the exoproteases into the surrounding environment. The degradation of hide powder azure allowed an immediate increase in respiration rate, also by long-term-starved cells. This suggests that metabolic systems are primed to respond to the availability of substrates, allowing the cells to recover rapidly. The regulation of exoprotease activity was also studied and found to be different in the two strains. Casamino Acids repressed exoprotease activity in Pseudomonas sp. strain S9, whereas a mechanism similar to catabolite repression was found for Vibrio sp. strain S14 in that glucose repressed activity and cyclic AMP reversed this effect. The exoproteases appeared to be metalloproteinases because the addition of EDTA to cell-free starvation supernatants from both strains significantly inhibited the activity of the proteases.     

Linkages between deoxyribonucleic acid synthesis and cell division in Myxococcus xanthus.

Addition of chloramphenicol or 0.5 M glycerol to growing Myxococcus xanthus resulted in an immediate cessation of cell division and 40% net increase in deoxyribonucleic acid (DNA). Although the chloramphenicol-treated cells divided in the presence of nalidixic acid after chloramphenicol was removed, glycerol-induced myxospores required DNA synthesis for subsequent cell division. Myxospores prepared from chloramphenicol-treated cells lost this potential to divide in the presence of nalidixic acid. The "critical period" of DNA synthesis necessary for cell division after germination overlapped in time (3 to 5 h) with initiation of net DNA synthesis. The length of the critical period of DNA synthesis was estimated at 12 min, or 5% of the M. xanthus chromosome. The requirement for cell division during germination also involved ribonucleic acid and protein synthesis after DNA synthesis. The data suggest that replication at or near the origin of the chromosome triggers the formation of a protein product that is necessary but not sufficient for subsequent cell division; DNA termination is also required. During myxospore formation, the postulated protein is destroyed, thereby reestablishing and making apparent this linkage between early DNA synthesis and cell division.     

The production and release of an extracellular polysaccharide during starvation of a marine Pseudomonas sp. and the effect thereof on adhesion

A marine Pseudomonas sp. S9 produced and released an extracellular polysaccharide during complete energy and nutrient starvation in static conditions. The presence of the polysaccharide on the cell surface, demonstrable by immune transmission electron microscopy, correlated with changes in the degree of adhesion to hydrophobic surfaces. Polysaccharide coated cells showed a lower degree of adhesion than did cells devoid of the polymer. After 10 h of starvation, no ruthenium red stained antibody stabilized polysaccharides could be observed on the cell surface. The polysaccharide was not produced during growth since lysates of mid-log phase cells did not precipitate the antiserum. The relative proportions of sugars in the polysaccharide were 28% glucose, 35% N-acetylglucosamine and 37% N-acetylgalactosamine. The released polysaccharide did not significantly alter the physical parameters of surface tension and viscosity of the starvation regime. Cells starved in agitated conditions did not produce any extracellular polysaccharides and exhibited a different adhesion pattern to hydrophobic surfaces.Non-standard abbreviations FSS Four salt solution - GLC gas liquid chromatography - MS Mass spectrometry - NSS nine salt solution     

Effect of Inhibitors of Ribonucleic Acid and Protein Synthesis on the Cyclic Adenosine Monophosphate Stimulation of Plasmid ColE1 Replication

Addition of cyclic adenosine 3'-5'-monophosphate (c-AMP) to growing Escherichia coli cells, colicinogenic for the plasmid ColE1, results in a fourfold stimulation in the rate of synthesis of the plasmid deoxyribonucleic acid (DNA). The stimulation is transient (30 min) and is succeeded by a brief period (30 min) of cessation of plasmid DNA replication. The stimulation of ColE1 DNA replication also occurs in chloramphenicol-treated cells. Rifampin inhibits ColE1 DNA replication in the presence or absence of c-AMP. Employing thymine starvation conditions to stop ColE1 DNA synthesis, it was found that c-AMP, added during the period of thymine starvation, effected a stimulation in the amount of subsequent replication which took place when replicating conditions were restored. The stimulatory effect of c-AMP under these conditions was not prevented by chloramphenicol but was completely eliminated when rifampin was present. Under these conditions, when rifampin was added after the effect of c-AMP was allowed to occur, subsequent replication of the plasmid could take place, but only one round of replication occurred. A model to account for the c-AMP effects is presented.     

Responses to multiple-nutrient starvation in marine Vibrio sp. strain CCUG 15956.

The response of marine Vibrio sp. strain S14 (CCUG 15956) to long-term (48-h) multiple-nutrient starvation (i.e., starvation for glucose, amino acids, ammonium, and phosphate simultaneously) can be described as a three-phase process. The first phase, defined as the stringent control phase, encompasses an accumulation of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) and decreases in RNA and protein synthesis during the first 40 min. In the second phase, there is a temporary increase in the rates of RNA and protein synthesis between 1 and 3 h paralleling a decrease in the ppGpp pool. The third phase includes gradual decline in macromolecular synthesis after 3 h. Using two-dimensional gel electrophoresis of pulse-labeled proteins, a total of 66 proteins were identified as starvation inducible (Sti), temporally expressed throughout the three phases of starvation. The inhibition of protein synthesis during the first phase of starvation partly disrupted the subsequent temporally ordered synthesis of starvation proteins and prevented the expression of some late starvation proteins. It was also found that the early temporal class of starvation proteins, which included the majority of the Sti proteins, was the most essential for long-term survival. Vibrio sp. strain S14 cultures prestarved (1 h) for glucose, amino acids, ammonium, or phosphate as well as cultures exposed (1 h) to CdCl2 exhibited enhanced survival during the subsequent multiple-nutrient starvation in the presence of chloramphenicol or rifampin, while heat or the addition of cyclic AMP or nalidixic acid prior to starvation had no effect. It was demonstrated that amino acid starvation and CdCl2 exposure, which induced the stringent response, were the most effective in conferring enhanced survival. A few Sti proteins were common to all starvation conditions. In addition, the total number of proteins induced by multiple-nutrient starvation significantly exceeded the sum of those induced by starvation for each of the individual nutrients.     

Synergism of Leu-Lys rich antimicrobial peptides and chloramphenicol against bacterial cells

To investigate the antibiotic activity and synergistic effect, analogues were designed to increase not only net positive charge by Lys-substitution but also hydrophobic helix region by Leu-substitution from CA (1-8)-MA (1-12) hybrid peptide (CA-MA). In particular, CA-MA analogue P5 (P5), designed by flexible region (GIG-->P)-substitution, Lys- (positions 4, 8, 14, 15) and Leu- (positions 5, 6, 12, 13, 16, 17, 20) substitutions, showed potent antibacterial activity in minimal inhibition concentration (MIC) and minimal bactericidal concentration (MBC) without having hemolytic activity. In addition, P5 and chloramphenicol has potent synergistic effect against tested cell lines. As determined by propidium iodide (PI) staining, flow cytometry showed that P5 plus chloramphenicol-treated cells had higher fluorescence intensity than untreated, P5- and chloramphenicol-treated cells. The effect on plasma membrane was examined by investigating the transmembrane potential depolarizing experiments of S. aureus with P5 and chloramphenicol. The result showed that the peptide exerts its antibacterial activity by acting on the plasma membrane. Furthermore, P5 caused significant morphological alterations of S. aureus, as shown by scanning electron microscopy. Our results suggest that peptide P5 is an excellent candidate as a lead compound for the development of novel anti-infective agents and synergistic effects with conventional antibiotic agents but lack hemolytic activity.     

Exoprotease activity of Leuconostoc oenos in stress conditions

Exoprotease activity during 48 h of total energy and nutrient starvation was examined in Leuconostoc oenos X₂L isolated from wine. Starved cells after 2 h of incubation at 30 °C in citrate buffer, 0.05 mmol 1⁻¹ pH 5, showed greater extracellular proteolytic activity than at the onset of starvation. In the presence of 60 mg l⁻¹ SO₂ and 8% or 12% ethanol, the proteolytic activity was higher ; 10 mmol l⁻¹ Ca²⁺ and Mg²⁺ produced an increase in protease activity during starvation. Glucose and 2-deoxyglucose (2-DOG) were found to repress synthesis by 80% and 100%, respectively. Cyclic adenosine 3'-5'-phosphate increased the exoprotease activity and reverted the repression by glucose and 2-DOG. De novo synthesis of proteins was required for the exoprotease activity by cells submitted to stress conditions. The absence of protease activity in the supernatant fluids from chloramphenicol-treated cells indicated that the activity is a result of deliberate release and not of passive cell lysis.     

Effect of cerulenin on cellular autolytic activity and lipid metabolism during inhibition of protein synthesis in Streptococcus faecalis.

Cellular autolytic activity as well as lipid and lipoteichoic acid metabolism have been studied in cultures of Streptococcus faecalis receiving various combinations of the following treatments: chloramphenicol addition, starvation for an essential amino acid (valine), and cerulenin treatment. Lipoteichoic acid initially accumulated in chloramphenicol-treated and amino acid-starved cells and decreased relative to the cellular mass in cerulenin-treated cells. The relative phosphatidylglycerol content of amino acid-starved cultures or of cultures treated with either antibiotic rapidly decreased upon initiation of each treatment. In all cases, cerulenin initially stimulated diphosphatidylglycerol synthesis. Pretreatment of cultures with cerulenin prevented the inhibition of cellular synthesis autolysis normally observed during chloramphenicol treatment, but did not affect amino acid starvation-induced inhibition of autolytic activity. Variations in the levels of the nonionic lipid fraction, predominantly diglycerides, correlated best with the patterns of autolytic activity observed during chloramphenicol treatment, whereas variations in the levels of diphosphatidylglycerol and lipoteichoic acid correlated best with the patterns of autolytic activity observed during amino acid starvation. Components of the nonionic lipid fraction were demonstrated to inhibit autolytic activity 50% in whole cell and in cell wall assays at 60 and 120 nmol/mg (dry weight), respectively.     

Global analysis of the carbon starvation response of a marine Vibrio species with disruptions in genes homologous to relA and spoT.

The stringent control response, which involves a rapid accumulation of ppGpp, is triggered if the marine Vibrio sp. strain S14 is subjected to carbon and energy starvation. By means of high-resolution two-dimensional gel electrophoresis analysis, we addressed the role of the major ppGpp-synthesizing enzyme (RelA) in the regulation of the carbon starvation response of Vibrio sp. strain S14. The finding that a large number of the carbon starvation-induced proteins were underexpressed in the Vibrio sp. S14 relA mutant strain after the onset of glucose starvation suggests that a rapid accumulation of ppGpp is required for induction of many of the carbon starvation-induced proteins. However, it was also found that a majority of the carbon starvation-induced proteins were significantly less induced if the stringent control response was provoked by amino acid starvation. We therefore also addressed the notion that a carbon starvation-specific signal transduction pathway, complementary to the stringent control, may exist in Vibrio sp. strain S14. It was found that a majority of the proteins that were underexpressed in the relA mutant strain were also underexpressed in the Vibrio sp. S14 spoT mutant strain (csrS1). Interestingly, a large proportion of these underexpressed proteins were found to belong to a group of proteins that are not, or significantly less, induced by starvation conditions that do not promote starvation survival. On the basis of these observations and the finding that the csrS1 strain survives poorly but accumulates ppGpp in a fashion similar to the wild type during carbon and energy source starvation, the gene product of the csrS gene is suggested to be responsible for the mediation of a signal which is complementary to ppGpp and essential for the successful development of the starvation- and stress-resistant cell. This conclusion was also supported by experiments in which changes in phenotypic characteristics known to be induced during carbon starvation were studied. The starvation induction of the high-affinity glucose uptake system was found to be dependent on the csrS gene but not relA, and the synthesis of carbon starvation-specific periplasmic space proteins was dependent, at different times of starvation, on both the relA and the csrS gene products.     

Inhibition by antibiotics of the bacterial response to long-term starvation of Salmonella typhimurium and the colon microbiota of mice

The number of viable cells of two strains of Salmonella typhimurium and the number of viable cells and the cell size of the colon microbiota of mice were examined during non-growing conditions after exposure to antibiotics with known modes of action. Salmonella typhimurium starved for 1, 2, 4, 5, 12 and 20 d in a phosphate buffer saline solution and subsequently exposed for 2 and 6 h showed the following characteristics. The protein synthesis inhibitors gentamicin and tetracycline, the RNA synthesis inhibitor rifampicin and the membrane potential inhibitor polymyxin all impaired survival of starved cells. The reduction in the number of viable cells caused by the addition of gentamicin, rifampicin and polymyxin was generally more pronounced with extended exposure to energy and nutrient deprivation. Both 2- and 6-h exposure of tetracycline, however, had diminishing inhibitory effects after 20 d compared with 5 d of starvation. Control experiments to verify non-growing conditions in the starvation regime showed that DNA and cell wall synthesis inhibitors had no inhibitory effect after 24-h starvation. The rough mutant strain displayed a lower sensitivity to a hydrophobic rather than a hydrophilic inhibitor as compared to the smooth wild-type strain. The cell size reduction but not viability was partly prevented by protein synthesis inhibitors as seen for both in vivo and in vitro colon microbiota studies.     

Inhibition by antibiotics of the bacterial response to long-term starvation of Salmonella typhimurium and the colon microbiota of mice

The number of viable cells of two strains of Salmonella typhimurium and the number of viable cells and the cell size of the colon microbiota of mice were examined during non-growing conditions after exposure to antibiotics with known modes of action. Salmonella typhimurium starved for 1, 2, 4, 5, 12 and 20 d in a phosphate buffer saline solution and subsequently exposed for 2 and 6 h showed the following characteristics. The protein synthesis inhibitors gentamicin and tetracycline, the RNA synthesis inhibitor rifampicin and the membrane potential inhibitor polymyxin all impaired survival of starved cells. The reduction in the number of viable cells caused by the addition of gentamicin, rifampicin and polymyxin was generally more pronounced with extended exposure to energy and nutrient deprivation. Both 2- and 6-h exposure of tetracycline, however, had diminishing inhibitory effects after 20 d compared with 5 d of starvation. Control experiments to verify non-growing conditions in the starvation regime showed that DNA and cell wall synthesis inhibitors had no inhibitory effect after 24-h starvation. The rough mutant strain displayed a lower sensitivity to a hydrophobic rather than a hydrophilic inhibitor as compared to the smooth wild-type strain. The cell size reduction but not viability was partly prevented by protein synthesis inhibitors as seen for both in vivo and in vitro colon microbiota studies.     

Evidence for a role of rpoE in stressed and unstressed cells of marine Vibrio angustum strain S14

We report the cloning, sequencing, and characterization of the rpoE homolog in Vibrio angustum S14. The rpoE gene encodes a protein with a predicted molecular mass of 19.4 kDa and has been demonstrated to be present as a single-copy gene by Southern blot analysis. The deduced amino acid sequence of RpoE is most similar to that of the RpoE homolog of Sphingomonas aromaticivorans, sigma(24), displaying sequence similarity and identity of 63 and 43%, respectively. Northern blot analysis demonstrated the induction of rpoE 6, 12, and 40 min after a temperature shift to 40 degrees C. An rpoE mutant was constructed by gene disruption. There was no difference in viability during logarithmic growth, stationary phase, or carbon starvation between the wild type and the rpoE mutant strain. In contrast, survival of the mutant was impaired following heat shock during exponential growth, as well as after oxidative stress at 24 h of carbon starvation. The mutant exhibited microcolony formation during optimal growth temperatures (22 to 30 degrees C), and cell area measurements revealed an increase in cell volume of the mutant during growth at 30 degrees C, compared to the wild-type strain. Moreover, outer membrane and periplasmic space protein analysis demonstrated many alterations in the protein profiles for the mutant during growth and carbon starvation, as well as following oxidative stress, in comparison with the wild-type strain. It is thereby concluded that RpoE has an extracytoplasmic function and mediates a range of specific responses in stressed as well as unstressed cells of V. angustum S14.     

Methods for Increasing Survivability During Storage of Exponentially Growing Bacteria

A protocol has been developed for storing Gram (−) bacterial cells at 0°C, which allows greater than 90% of stored cells to retain colony-forming ability for up to 60 days. The protocol, which yields essentially identical results when used with Escherichia coli or Pseudomonas aeruginosa, does not enhance survivability of Bacillus cereus. The greatest and longest survival is enjoyed when exponentially growing cells in minimal-glucose medium are deprived of carbon for about 9 h, supplemented with 750 μg/ml chloramphenicol, and immediately placed at 0°C. By decreasing the period of carbon starvation from 9 to 5 h, or increasing the period of carbon starvation from 9 to 12 h, both the ultimate survival rate and kinetics of loss of culturability are affected. Survival enhancement induced by chloramphenicol is not similarly induced by kanamycin. Received: 12 April 1996 / Accepted: 20 May 1996     

Role of guanosine tetraphosphate in gene expression and the survival of glucose or seryl-tRNA starved cells of Escherichia coli K12

The concentration of guanosine 3′,5′-bispyrophosphate (ppGpp) increases in bacteria in response to amino acid or carbon/energy source starvation. An Escherichia coli K12 ΔrelAΔspoT mutant lacking the ability to synthesize ppGpp lost viability at an increased rate during both glucose and seryl-tRNA starvation. Also, the deleterious effect of chloramphenicol on starved wild-type cells could be overcome by inducing expression of RelA from a plasmid carrying the relA gene transcribed from a tac promoter, prior to starvation and chloramphenicol treatment. As demonstrated by two dimensional gel electrophoresis, this induction of the RelA protein resulted in global alterations in gene expression including increased synthesis of some rpoS-dependent proteins. The ΔrelAΔspoT mutant maintained high expression of several ribosomal proteins during starvation and appeared to exhibit significantly decreased translational fidelity, as demonstrated by an unusual heterogeneity in the isoelectric point of several proteins and the failure to express higher molecular weight proteins during starvation. Moreover, both rpoS-dependent and independent genes failed to exhibit increased expression in the mutant. It is suggested that the deleterious effects on the cells of the relA, spoT deletions are not due solely to the inability of these cells to induce the sigma factor σ^s, but also to deficiencies in translational fidelity and failure to exert classical stringent regulation.     

Role of protein degradation in the survival of carbon-starved Escherichia coli and Salmonella typhimurium.

When an Escherichia coli K-12 culture was starved for glucose, 50% of the cells lost viability in about 6 days. When a K-12 mutant lacking five distinct peptidase activities, CM89, was starved in the same manner, viability was lost much more rapidly; 50% of the cells lost viability in about 2 days, whereas a parent strain lacking only one peptidase activity lost 50% viability in about 4 days. Compared with the wild-type strain and with its parent strain CM17, CM89 was defective in both protein degradation and protein synthesis during carbon starvation. Similar results were obtained with glucose-starved Salmonella typhimurium LT2 and LT2-derived mutants lacking various peptidase activities. An S. typhimurium mutant lacking four peptidases, TN852, which was deficient in both protein degradation and synthesis during carbon starvation (Yen et al., J. Mol. Biol. 143:21-33, 1980), was roughly one-third as stable as the isogenic wild type. Isogenic S. typhimurium strains that lacked various combinations of three of four peptidases and that displayed protein degradation and synthesis rates intermediate between those of LT2 and TN852 (Yen et al., J. Mol. Biol. 143:21-33, 1980) displayed corresponding stabilities during carbon starvation. These results point to a role for protein degradation in the survival of bacteria during starvation for carbon.     

Starvation-Induced Effects on Bacterial Surface Characteristics

Changes in bacterial surface hydrophobicity, charge, and degree of irreversible binding to glass surfaces of seven marine isolates were followed during starvation. The degree of hydrophobicity was measured by hydrophobic interaction chromatography and by two-phase separation in a hexadecane-water system, whereas changes in charge were measured by electrostatic interaction chromatography. All isolates underwent the starvation-induced responses of fragmentation, which is defined as division without growth, and continuous size reduction, which results in populations with increased numbers of smaller cells. The latter process was also responsible for a significant proportion of the total drop in cell volume; this was observed by noting the biovolume (the average cell multiplied by the number of bacteria) of a population after various times of starvation. Four strains exhibited increases in both hydrophobicity and irreversible binding, initiated after different starvation times. The most hydrophilic and most hydrophobic isolates both showed a small increase in the degree of irreversible binding after only 5 h, followed by a small decrease after 22 h. Their hydrophobicity remained constant, however, throughout the entire starvation period. On the other hand, one strain, EF190, increased its hydrophobicity after 5 h of starvation, although the degree of irreversible binding remained constant. Charge effects could not be generally related to the increase in irreversible binding. Scanning electron micrographs showed a large increase in surface roughness throughout the starvation period for all strains that showed marked changes in physicochemical characteristics.     

Role of guanosine tetraphosphate in gene expression and the survival of glucose or seryl-tRNA starved cells of Escherichia coli K12

The concentration of guanosine 3,5-bispyrophosphate (ppGpp) increases in bacteria in response to amino acid or carbon/energy source starvation. An Escherichia coli K12 relAspoT mutant lacking the ability to synthesize ppGpp lost viability at an increased rate during both glucose and seryl-tRNA starvation. Also, the deleterious effect of chloramphenicol on starved wild-type cells could be overcome by inducing expression of RelA from a plasmid carrying the relA gene transcribed from a tac promoter, prior to starvation and chloramphenicol treatment. As demonstrated by two dimensional gel electrophoresis, this induction of the RelA protein resulted in global alterations in gene expression including increased synthesis of some rpoS-dependent proteins. The relAspoT mutant maintained high expression of several ribosomal proteins during starvation and appeared to exhibit significantly decreased translational fidelity, as demonstrated by an unusual heterogeneity in the isoelectric point of several proteins and the failure to express higher molecular weight proteins during starvation. Moreover, both rpoS-dependent and independent genes failed to exhibit increased expression in the mutant. It is suggested that the deleterious effects on the cells of the relA, spoT deletions are not due solely to the inability of these cells to induce the sigma factor ^s, but also to deficiencies in translational fidelity and failure to exert classical stringent regulation.     

Centriole behavior in chloramphenicol-treated eggs of the sand dollar,Dendraster excentricus

Summary This electron microscope study was undertaken to test the prediction made from an indirect assay method for mitotic centers (centrioles), that chloramphenicol inhibits centriole replication during first cleavage division in the eggs of the sand dollar,Dendraster excentricus. Extensive serial sectioning through both untreated and chloramphenicol-treated eggs, coupled with thorough examination of these sections, has demonstrated that 57% of the untreated eggs and 14% of the chloramphenicol-treated eggs contained paired centrioles at a time when centriole pairs normally exist. This study thus gives direct evidence that chloramphenicol inhibits centriole replication.     

Postreplication DNA repair in Escherichia coli cells. III. Repair independent of the presence of pKM101 and COLIb-P9 plasmids

The presence of pKM101 or ColIb-P9 plasmids in E. coli leads to the increase in the survival of UV-irradiated cells of wild type and of polAI, recB21 recC22 and dnaGts mutants; it does not change the survival of recA13 and lex3 mutants and does not influence kinetics and efficiency of postreplication repair (PRR) of DNA in cells of all the strains examined (with the exception of PG3 dnaGts mutant whose PRR of DNA in the presence of pKM101 plasmid is somewhat lower). The survival of both plasmid-containing and plasmid-free bacteria treated with chloramphenicol decreases in the same degree, but the survival of chloramphenicol-treated recA13, lex3 recB21 rec C22 mutants does not change. The pKM101 plasmid does not lend the dnaGts mutant a new capacity of repairing postreplication gaps with the participation of inducible component of PRR; the chloramphenicol-sensitive component of PRR is absent in this mutant. Plasmid and plasmid-free E. coli strains of wild type and of the polA1 mutant do not differ by the kinetics and level of inducible chloramphenicol-sensitive component of PRR of DNA.