Isolation and Mapping of Phosphotransferase Mutants in Escherichia coli

Mutants of Escherichia coli K-12 defective in enzyme I or Hpr, the two common components of the phosphoenolpyruvate-dependent phosphotransferase system, were isolated by a simple, direct method. The ptsI locus, the structural gene for enzyme I, and the ptsH locus, the site of mutations leading to loss of Hpr activity, are adjacent genes and could be part of a single operon. These two genes lie between the purC and supN markers in the order: strA... guaB-purC-ptsI-ptsH-supN-dsdA... his.     

T-Even Bacteriophage-Tolerant Mutants of Escherichia coli B: I. Isolation and Preliminary Characterization

A general procedure is described for isolation of T-even phage-tolerant mutants of Escherichia coli. Two such mutants of E. coli B have been examined in some detail. These mutants adsorb T-even phages but are unable to release viable progeny. Under certain conditions, viability of the cells is completely unaffected by phage infection in one mutant, and there is but a slight decrease in colony-forming ability in the other. Phage deoxyribonucleic acid (DNA) is injected into these cells, as shown by the formation of phage-specific enzymes, but it is not degraded to acid-soluble material. Some phage DNA replication occurs in both strains. The mutants are both more resistant to ultraviolet light than is the parent strain.     

Isolation and Mapping of Polynucleotide Phosphorylase Mutants of Escherichia coli

Three strains of Escherichia coli with altered polynucleotide phosphorylase, Q7, Q13, and Q27, were isolated by screening clones from heavily mutagenized cultures for low levels of the enzyme. The three mutations were found to cotransduce with argG and asp, and the pnp locus which they define was mapped with respect to these loci. An explanation for the nonreciprocal cotransduction frequencies observed with asp is provided by the demonstration of an unlinked asp-suppressing locus.     

Isolation and Properties of Fumarate Reductase Mutants of Escherichia coli

Escherichia coli produces two enzymes which interconvert succinate and fumarate: succinate dehydrogenase, which is adapted to an oxidative role in the tricarboxylic acid cycle, and fumarate reductase, which catalyzes the reductive reaction more effectively and allows fumarate to function as an electron acceptor in anaerobic growth. A glycerol plus fumarate medium was devised for the selection of mutants (frd) lacking a functional fumarate reductase by virtue of their inability to use fumarate as an anaerobic electron acceptor. Most of the mutants isolated contained less than 1% of the parental fumarate reduction activity. Measurements of the fumarate reduction and succinate oxidation activities of parental strains and frd mutants after aerobic and anaerobic growth indicated that succinate dehydrogenase was completely repressed under anaerobic conditions, the assayable succinate oxidation activity being due to fumarate reductase acting reversibly. Fumarate reductase was almost completely repressed under aerobic conditions, although glucose relieved this repression to some extent. The mutations, presumably in the structural gene (frd) for fumarate reductase, were located at approximately 82 min on the E. coli chromosome by conjugation and transduction with phage P1. frd is very close to the ampA locus, and the order of markers in this region was established as ampA-frd-purA.     

Behavioral Mutants of DROSOPHILA MELANOGASTER. I. Isolation and Mapping of Mutations Which Decrease Flight Ability

A flight test box was developed and used in the isolation and initial characterization of Drosophila melanogaster mutants defective in flight behavior. Forty-eight mutants were isolated from F₁ progeny of ethyl methanesulfonate-treated males. Genetic mapping and complementation tests show that the mutations reside at thirty-four different sites on the X chromosome. Different mutants show different degrees of flight ability compared to controls. Forty-six mutations are recessive, while two appear to be semi-dominant with respect to flight behavior. In addition to flight defects, five mutants have visible defects, five behave as temperature-sensitive lethals and three exhibit abnormal electro-retinograms. Alleles of each of the previously known behavioral mutations, Hyperkinetic, ether à go-go and Shaker were found. Preliminary studies also suggest that the flight behavioral phenotype of mutations at seven sites is affected by the temperature at which the flies develop.     

Genetic Mapping of Mutations Affecting Phosphoglucose Isomerase and Fructose Diphosphatase in Escherichia coli

The loci on the Escherichia coli genome of mutations affecting phosphoglucose isomerase (pgi) and fructose diphosphatase (fdp) have been determined by conjugation and transduction experiments, chiefly three-factor crosses. The loci for these two constitutive enzymes of central intermediary metabolism lie in the same region of the chromosome, but they are not cotransducible. The order of some markers in this region of the chromosome is arg(ACFH) metA pgi malB uvrA fdp pyrB thr.     

Isolation and Some Properties of Cell Envelope Altered Mutants of Escherichia coli

Mutants of Escherichia coli which have a defect in their permeability barrier were selected. The technique used was to employ a strain of E. coli having a deletion in the gene for lactose permease and to select for mutants which can grow on lactose at 40 C. Twenty such mutants were isolated and six of these were found to be more sensitive to actinomycin D, sodium deoxycholate, and sodium dodecyl sulfate than was the parental strain. They were also more sensitive to the antibiotics vancomycin and bacitracin, which inhibit peptidoglycan biosynthesis. These mutants were no more sensitive to several different colicins or phages than was the wild-type strain. One of the mutants selected by this technique has an abnormal morphology when grown on certain carbon sources in minimal medium, and this mutant is more extensively studied in the accompanying paper.     

Resistance of Escherichia coli to Penicillins I. Genetic Study of Some Ampicillin-Resistant Mutants.

Eriksson-Grennberg, Kerstin G. (University of Uppsala, Uppsala, Sweden), Hans G. Boman, J. A. Torbj?rn Jansson, and Sone Thorén. Resistance of Escherichia coli to penicillins. I. Genetic study of some ampicillin-resistant mutants. J. Bacteriol. 90:54-62. 1965.-A number of ampicillin-resistant mutants have been isolated and characterized. Of these strains, two groups have been genetically investigated: members of one group, which are moderately resistant to ampicillin (Amp(r) (10)) carry mutations in a locus which we have designated ampA; another strain, which is resistant to high levels (50 mug/ml) of ampicillin, is a multistep mutant for which a genotype cannot yet be written. The phenotype of this strain has been designated Amp(r) (50). The location of ampA was studied by the interrupted-conjugation technique, with argF, metB, mtl, and serA as reference markers. The phenotypic expression was the same for ampA and argF. These experiments, as well as recombination without selection for ampicillin resistance, indicate that ampA is located between argF and pyrB. "Broken slopes" on the recombinant curves and failure to demonstrate cotransduction make a more accurate mapping difficult. Phage P1bt transduced ampA from resistant donors to sensitive recipient strains with a frequency of 5 x 10(-7). The ampA locus segregated in conjugation and transduction experiments with an Amp(r) (50) donor strain, but neither method gave a genetic transfer of high resistance to ampicillin. Penicillinase activity was demonstrated in two independent mutants carrying the ampA locus.     

Genetic Analysis of Flagellar Mutants in Escherichia coli

Flagellar mutants in Escherichia coli were obtained by selection for resistance to the flagellotropic phage chi. F elements covering various regions of the E. coli genome were then constructed, and, on the basis of the ability of these elements to restore flagellar function, the mutations were assigned to three regions of the E. coli chromosome. Region I is between trp and gal; region II is between uvrC and aroD; and region III is between his and uvrC. F elements carrying flagellar mutations were constructed. Stable merodiploid strains with a flagellar defect on the exogenote and another on the endogenote were then prepared. These merodiploids yielded information on the complementation behavior of mutations in a given region. Region III was shown to include at least six cistrons, A, B, C, D, E, and F. Region II was shown to include at least four cistrons, G, H, I, and J. Examination of the phenotypes of the mutants revealed that those with lesions in cistron E of region III produce "polyhooks" and lesions in cistron F of region III result in loss of ability to produce flagellin. Mutants with lesions in cistron J of region II were entirely paralyzed (mot) mutants. Genetic analysis of flagellar mutations in region III suggested that the mutations located in cistrons A, B, C, and E are closely linked and mutations in cistrons D and F are closely linked.     

Isolation of Cadmium- and Mercury-sensitive Mutants of Escherichia coli and Some Factors Influencing Their Sensitivities

Several Cd²⁺ hypersensitive and Hg²⁺ sensitive mutants of Escherichia coli K-12 were isolated after repeated mutagenesis with nitrosoguanidine. The Cd-hypersensitive mutant, CD17P, could not grow in a chemically defined liquid medium containing 0.5 μm Cd²⁺, and the growth of Hg-sensitive mutant, HG17P-52, was inhibited by 0.9 μm Hg²⁺. Thus, CD 17P and HG17P-52 were respectively about 1000 fold and 4 fold more sensitive than the parental strain.

Both mutants were also considerably more sensitive to Zn²⁺ than their parent, but they did not show any appreciable change in sensitivity to other metals tested. Among the various metabolites and chemicals tested, reducing agents such as cysteine, dithiothreitol and vitamin C showed a protective effect against metal toxicity. Reduced glutathione was effective only against Hg²⁺. EDTA specifically and efficiently reversed only Cd²⁺ toxicity.     

Isolation and Characterization of Mutants of Colicin Plasmids E1 and E2 After Mu Bacteriophage Infection

Cells colicinogenic for the colicin plasmids E1 or E2 (Col E1 and Col E2, respectively) were selected for a loss of colicin production after infection with bacteriophage Mu. Extrachromosomal deoxyribonucleic acid that was larger than the original colicin plasmids was found in such cells. A small insertion mutant in Col E1 deoxyribonucleic acid affecting active colicin production without affecting either expression of colicin immunity or Col E1 deoxyribonucleic acid replication was found. Cells carrying this Col E1 plasmid mutant do not exhibit the lethal event associated with colicin E1 induction, suggesting that synthesis of active colicin is required for killing during induction. The altered Col E2 plasmid, containing an insertion at least as large as phage Mu, was maintained unstably in the mutants examined.     

Escherichia coli K-12 Mutants Resistant to Nalidixic Acid: Genetic Mapping and Dominance Studies

Escherichia coli K-12 strains tested so far (approximately 20) can be separated into three groups on the basis of their abilities to form colonies on nutrient agar supplemented with nalidixic acid (NAL): (i) Nal(s) or wild type (no growth at 1 to 2 mug/ml); (ii) NalA(r) (growth at 40 mug/ml or higher); and (iii) NalB(r) (growth at 4 mug/ml, but no growth at 10 mug/ml). The NalA(r) group has a spectrum of sensitivity ranging from 60 to over 100 mug/ml. All Hfr strains of the NalA(r) and NalB(r) groups transfer NAL resistance to recipient cells at genetic loci which are at 42.5 +/- 0.5 and 51 +/- 1 min, respectively, on the Taylor-Trotter map. Some members of the NalA(r) group also have the genetic locus for NalB(r). The nalA(s) allele is completely dominant to nalA(r) in a partial diploid configuration. In haploids, nalA(r)-nalB(r) is phenotypically NalA(r); nalA(r)-nalB(s) is NalA(r); and nalA(s)-nalB(r) is NalB(r). The map location of nalA and the easy differentiation between NalA(r) and NalA(s) allow this marker to be used as a counterselector in bacterial conjugation experiments.     

Characterization and Genetic Mapping of Phosphoglucoisomerase Mutations in Mannitol-Negative Mutants of Pseudomonas aeruginosa

Phosphoglucoisomerase (pgi) mutations in a number of independently isolated mannitol-negative mutants of Pseudomonas aeruginosa PAO1 were mapped on the chromosome by plasmid FP5-mediated conjugation and by cotransduction with the generalized transducing phages G101 and F116L. Mutant allele pgi-9001 exhibited linkage to ilvB, C-9059 (46–85%), car-9003 (93–100%), and pur-9047 (70%), but not with met-9011, in FP5-mediated conjugational crosses. All known pgi mutations and several previously uncharacterized mannitol-negative mutations exhibited transductional linkage to two independent car mutations at frequencies ranging from 13% to 42% and 53% to 99%, in transductional crosses mediated by phages G101 and F116L respectively. These pgi and mannitol-negative mutations also were cotransducible at very low frequencies (<1%) with two independent ilv mutations. Cotransduction of the car and ilv loci could not be detected. These data suggest the location of pgi within the first minute of the P. aeruginosa chromosome closely linked to the car marker and probably between the ilv and car loci. All of the mannitol-negative mutations that exhibited linkage to the car and ilv loci were characterized as pgi mutations by enzyme assays. A phenotypically similar, mannitol-negative mutatant was shown to contain a mutation in glucose-6-phosphate dehydrogenase (zwf-9012) that maps to a different region on the chromosome. Received: 26 April 1996 / Accepted: 10 June 1996     

Mutants of Escherichia coli with altered deoxyribonucleases. II. Isolation and characterization of mutants for exonuclease I

Mutants of Escherichia coli K12 deficient in exonuclease I (xon^?)³ were identified by enzymic assay of randomly selected, heavily mutagenized clones. From one of the six mutants of independent origin a thermolabile variant of exonuclease I was partially purified and identified, indicating that the mutation is probably in a structural gene for the enzyme. Transduction of this mutation into a recB^? recC^? strain did not result in the suppression of any of the phenotypic traits of the recipient. Although the five other mutants also appear to have temperature-sensitive exonuclease I activities in crude extracts, these enzymes were not sufficiently stable to permit purification. These latter mutations were of the xonA^? type; they produced a temperature-dependent suppression of the sensitivity to ultraviolet light and to mitomycin C manifested by a recB^? recC^? strain. None of the six mutations were of the sbcB^? type; that is, they did not suppress the recombination deficiency of a recB^? recC^? strain.In experiments with bacteriophage Plke, the six mutations were 41 to 62% cotransducible with the his region of E. coli. Heterozygous F′-merodiploids were constructed and studied for possible complementation of exonuclease I activity. All six mutations and an sbcB^? mutation were recessive to the wild-type alleles, and all were found to belong to a single complementation group. The results suggest that alterations of a structural gene for exonuclease I may result in the indirect suppression of the ultraviolet and mitomycin sensitivity manifested by recB^? recC^? strains.     

Genetic Analysis of Recombination-Deficient Mutants of Escherichia coli K-12 Carrying rec Mutations Cotransducible with thyA

The rec mutations carried by 20 strains of Escherichia coli K-12 which are defective in genetic recombination and sensitive to ultraviolet light and X rays, and whose lambda lysogens show spontaneous phage production, have been mapped near thyA. In 15 of the strains, the rec mutation fails to complement recB21 but complements rec-22. The other five strains carry a rec mutation which complements recB21 but not rec-22. These mutations map closer to thyA than those which fail to complement recB21. They therefore appear to be defective in a different recombination gene, denoted recC. The order of recB and recC on the linkage map of E. coli K-12 is thyA-recC-recB-argA.     

Isolation and Properties of Escherichia coli Mutants Which Are Nonpermissive for the Growth of Phage Lambda

By selecting survivors of λ phage infection, mutants of Escherichia coli K12 that block reproduction cycle of the phage have been isolated. Fourteen of these phage-tolerant mutants (lam mutants) were chosen and characterized biochemically and genetically. It was shown that these mutants were tolerant to infection by all the lambdoid phages, except for few cases, but they were susceptible to infection by a non-lambdoid temperate phage (φ299), P1 or T phages. The mutants can be divided into at least three groups: (1) A mutant (lam 16) strain that seems to block normal penetration of phage DNA: (2) Three mutant (lam 64, lam 67 and lam 71) strains that block an “early” step(s) of phage growth, including phage DNA synthesis: (3) Six mutant (lam 24, lam 25, lam 26, lam 27, lam 646 and lam 6) strains that block normal functioning of the gene E products and produce unusual head structures. Some lambdoid phages and λ mutants that overcome the interference by the lam mutations have been obtained, and were used as tools for characterizing the host mutations. Two (lam 12 and lam 13) mutant strains and one (lam 1) mutant were inferred as affecting the expression of “late” genes, and early gene, respectively, by this test.     

Amount of Colicin Release in Escherichia coli Is Regulated by Lysis Gene Expression of the Colicin E2 Operon

The production of bacteriocins in response to worsening environmental conditions is one means of bacteria to outcompete other microorganisms. Colicins, one class of bacteriocins in Escherichia coli, are effective against closely related Enterobacteriaceae. Current research focuses on production, release and uptake of these toxins by bacteria. However, little is known about the quantitative aspects of these dynamic processes. Here, we quantitatively study expression dynamics of the Colicin E2 operon in E. coli on a single cell level using fluorescence time-lapse microscopy. DNA damage, triggering SOS response leads to the heterogeneous expression of this operon including the cea gene encoding the toxin, Colicin E2, and the cel gene coding for the induction of cell lysis and subsequent colicin release. Advancing previous whole population investigations, our time-lapse experiments reveal that at low exogenous stress levels all cells eventually respond after a given time (heterogeneous timing). This heterogeneous timing is lost at high stress levels, at which a synchronized stress response of all cells 60 min after induction via stress can be observed. We further demonstrate, that the amount of colicin released is dependent on cel (lysis) gene expression, independent of the applied exogenous stress level. A heterogeneous response in combination with heterogeneous timing can be biologically significant. It might enable a bacterial population to endure low stress levels, while at high stress levels an immediate and synchronized population wide response can give single surviving cells of the own species the chance to take over the bacterial community after the stress has ceased.     

The Genetic Basis for Mucoidy and Radiation Sensitivity in capR (lon) Mutants of E. coli K-12

CapR mutants of E. coli K-12 overproduce capsular polysaccharide (mucoid phenotype) and enzymes involved in capsular polysaccharide synthesis, and they are sensitive to radiation. It has been uncertain whether both properties are mediated by damage to a single cistron or by a polar effect on a second cistron in the same operon. Introduction of a polarity suppressor caused no change in the overproduction of polysaccharide, in the enzymes of polysaccharide synthesis or in radiation sensitivity of the capR mutant. Thus mucoidy and radiation sensitivity resulting from capR (lon) mutations are both the consequences of impairment of the same cistron. The experiments demonstrate the advantage of the use of polarity suppressors (over conventional nonsense suppressors) in determining whether pleiotropic effects of a mutation are the result of polarity.