Use of gene fusions to determine the orientation of gene phoA on the Escherichia coli chromosome

We present genetic evidence which demonstrates that the phoA gene is transcribed in the clockwise direction on the Escherichia coli chromosome, in contrast to an earlier proposal. Our conclusion is based on analysis of various genetic fusions between the lac operon and the phoA gene.

envB mutations confer UV-sensitivity to Salmonella typhimurium and UV-resistance to Escherichia coli

An envB mutation isolated in Salmonella typhimurium LT2 was transferred by conjugation to Escherichia coli K-12. The mutation produced the same alterations in E. coli as in S. typhimurium concerning cell shape, sensitivity to drugs, autolysis, and fermentation of carbohydrates. However, although the mutation conferred sensitivity to UV irradiation in Salmonella, in E. coli it behaved as a genuine envB mutation producing resistance to UV inactivation. The fact that the mutation produced opposite effects in the survival of UV-irradiated S. typhimurium and E. coli discloses an intriguing difference between these closely related species.

Immune responses in mice against herpes simplex virus: mechanisms of protection against facial and ganglionic infections

We performed experiments with mice to determine the nature of the immune response(s) that prevents primary infections of the skin and the trigeminal ganglia with herpes simplex virus. Immunization with infectious herpes simplex virus, inactivated virus, or material enriched for viral glycoproteins protected hairless mice against primary facial and ganglionic infections. Live and inactivated viruses induced neutralizing antibodies, whereas glycoprotein material did not. Instead, glycoprotein material induced antibodies that were largely directed against two glycopolypeptides with molecular weights of 120,000 to 130,000. Hairless mice immunized with glycoprotein material responded faster than control mice in the synthesis of neutralizing antibodies after challenge with infectious virus. Congenital athymic BALB/c (nu/nu) mice were protected against primary facial infections after immunization with glycoprotein material, but glycoprotein-specific antibodies were not induced.

Molecular cloning of the fnr gene of Escherichia coli K12

Mutations in the fnr gene of Escherichia coli have pleiotrophic effects leading to deficiencies in the reduction of fumarate and nitrate, hydrogen production and the ability to grow anaerobically with fumarate or nitrate as terminal electron acceptors. Transducing phages (lambda fnr) carrying the wild-type fnr gene were isolated from populations of artificially-constructed recombinant lambda phages by their ability to complement the lesions of fnr mutants. The lambda fnr phages restored anaerobic growth with fumarate and nitrate as electron acceptors and as prophages, they promoted normal synthesis of fumarate reductase, nitrate reductase and hydrogenase in fnr mutants. Five independently-isolated lambda fnr phages each contained a R.HindIII fragment (11.5 kilobases) that possessed three internal R.EcoRI targets and had inserted with the same orientation relative to the phage. A physical map of the fnr region was constructed by restriction analysis and flanking fragments were identified by DNA : DNA hybridization.

Genetic circularity of the Pseudomonas aeruginosa PAO chromosome

Genetic circularity of the Pseudomonas aeruginosa PAO chromosome was demonstrated by a series of two- and three-factor crosses and double-selection experiments with Cma plasmids FP2, FP5, FP110, and R68.45. A range of additional markers, including catabolic markers, were located on the chromosome map. Plasmid FP2, known to have a major origin of chromosome transfer (0 min) was shown to have at least one other minor origin from which it can transfer the chromosome in the direction opposite to that found for the major origin.

Repression of ant synthesis early in the lytic cycle of phage P22

Using SDS-polyacrylamide gel electrophoresis to study the early expression of P22 genes we show that early expression of the ant-gene (imm I region) is turned off after 6-8 min, independent of the 'late' acting mnt-repressor. A semi-clear mutant called cir5 is defective for this early ant turn-off. The mutation cir5 maps in the imm I region of P22 between genes mnt and ant. P22 cir5 mutants are defective for a repressor which acts in trans to regulate early ant synthesis. There appears to be no absolute requirement of the cir5 allele for the establishment of lysogeny. The overproduction of ant in the P22 cir5 mutant leads to a marked increase in abortive infections, killing the infected cells. The cir5-phenotype can be suppressed by an ant- mutation.

Menaquinone biosynthesis in Bacillus subtilis: isolation of men mutants and evidence for clustering of men genes

Menaquinone (vitamin K2)-deficient mutants of Bacillus subtilis were selected by simultaneous resistance to two aminoglycoside antibiotics. These men mutants fell into two groups: group I, in which the nutritional requirement was satisfied either by o-succinylbenzoic acid or by 1,4-dihydroxy-2-naphthoic acid; and group II, comprising those capable of growing only when supplemented with 1,4-dihydroxy-2-naphthoic acid. The latter group could be further subdivided into two classes on the basis of syntrophy experiments, fine-structure genetic mapping, and in vitro complementation by cell-free extracts (Meganathan et al., J. Bacteriol., 145:328-332, 1981). These subclasses of group II defined the menB and menE genes, whereas group I appeared to comprise mutations in the menC and menD genes. All of the men mutations tested, whether occurring in menB, menE, or menC,D, could be placed by genetic mapping with bacteriophage PBS1 between bioB and ald on the B. subtilis genome.

Deletion map of the Escherichia coli structural gene for alkaline phosphatase, phoA

Lambda transducing phages containing portions of the phoA gene have been isolated and used to construct a deletion map of the phoA gene. The isolation of a plaque-forming lambda transducing phage carrying the entire phoA gene is also described. Two new methods for screening or selection of mutants that have altered levels of alkaline phosphatase activity are reported.

Introduction of bacteriophage Mu into bacteria of various genera and intergeneric gene transfer by RP4::Mu

The host range of coliphage Mu was greatly expanded to various genera of gram-negative bacteria by using the hybrid plasmic RP4::Mu cts, which is temperature sensitive and which confers resistance to ampicillin, kanamycin, and tetracycline. These drug resistance genes were transferred from Escherichia coli to members of the general Klebsiella, Enterobacter, Citrobacter, Salmonella, Proteus, Erwinia, Serratia, Alcaligenes, Agrobacterium, Rhizobium, Pseudomonas, Acetobacter, and Bacillus. Mu phage was produced by thermal induction from the lysogens of all these drug-resistant bacteria except Bacillus. Mu phage and RP4 or the RP4::Mu plasmid were used to create intergeneric recombinant strains by transfer of some genes, including the arylsulfatase gene, between Klebsiella aerogenes and E. coli. Thus, genetic analysis and intergeneric gene transfer are possible in these RP4::Mu-sensitive bacteria.

Kinetic and physical properties of the L-malate-NAD+ oxidoreductase from Methanospirillum hungatii and comparison with the enzyme from other sources

The L-malate-NAD+ oxidoreductase of Methanospirillum hungatii was purified to homogeneity by using Blue Sepharose and ADP-Sepharose affinity chromatography. The molecular weight was estimated as 61 700 +/- 1900 by gel filtration and 64 200 +/- 1200 by ultracentrifugation. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis indicated that the protein is composed of two polypeptide chains, each corresponding to 31 350 +/- 2150 daltons. Inhibition patterns obtained for malate, alpha-oxoglutarate and ADP established that the sequential reaction mechanism was ordered, with NADH serving as the first substrate. Intracellular concentrations of oxaloacetate approximated the Km value of 27 microM, but NADH was present at less than Km values. Comparison of the amino-acid composition of the L-malate-NAD+ oxidoreductase of M. hungatii and 22 others from prokaryotic and eukaryotic cells revealed a significant direct relationship between average hydrophobicity and the frequency of non-polar side chains, as well as a significant indirect relationship between average hydrophobicity and the polarity ratio. Calculations based on amino-acid-composition data indicated significant composition similarity between pairs of mammalian-cytoplasmic or pairs of mitochondrial L-malate-NAD+ oxidoreductases from various sources, but no significant composition similarity between any of the pairs of bacterial species examined.

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments

Colony counts of acetate-, propionate- and L-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers. Anaerobic mineralization of acetate, propionate and L-lactate was studied in the presence and in the absence of sulfate. In freshwater and in marine sediments, acetate and propionate were oxidized completely with concomitant reduction of sulfate. L-Lactate was always fermented. Lactate-oxidizing, sulfate-reducing bacteria could only be isolated from marine sediments, they belonged to the genus Desulfobacter and oxidized only acetate and ethanol by sulfate reduction. Propionate-oxidizing, sulfate-reducing bacteria belonged to the genus Desulfobulbus. They were isolated from freshwater as well as from marine sediments and showed a relatively large range of usable substrates: hydrogen, formate, propionate, L-lactate and ethanol were oxidized with concomitant sulfate reduction. L-Lactate and pyruvate could be fermented by most of the isolated strains.

Restricted replication of human hepatitis A virus in cell culture: intracellular biochemical studies

When hepatitis A virus was inoculated into Vero cells, virus-specified protein and RNA synthesis was detected. Production of viral protein was detected by electrophoretic analysis in polyacrylamide gels by using a double-label coelectrophoresis and subtraction method which eliminated the contribution of host protein components from the profiles of virus-infected cytoplasm. Eleven virus-specified proteins were detected in the net electrophoretic profiles of hepatitis A virus-infected cells. The molecular weights of these proteins were very similar to those detected in cells infected with poliovirus type 1. Virus-specified protein synthesis could be detected at 3 to 6 h and continued for at least 48 h postinfection, but no significant effect on host-cell macromolecular synthesis was observed. Limited viral RNA replication occurred between 2 and 6 h postinfection. The genomic RNA of hepatitis A virus was extracted and shown to be capable of infecting cells and inducing the same set of proteins as intact virus, indicating that the RNA genome is positive stranded. Progeny virus was never detected in the supernatant fluids of infected cell cultures, and the cells showed no observable cytopathology, even though hepatitis A virus-specific proteins and antigens were being produced. The nature of the defect in the replicative cycle of hepatitis A virus in this system remains unknown.

Interactions between murine macrophages and obligate intracellular protozoa

The diversity of interactions between obligate intracellular protozoa and murine macrophages is just being elucidated. Protozoa of the genera Toxoplasma, Leishmania, and Trypanosoma all enter and replicate within macrophages. This review describes similarities and differences among these organisms with regard to entry mechanisms, sites of replication in the phagolysosomal system, metabolic requirements, effects on macrophage function, macrophage handling of protozoal antigens, the relationship to genetics of immune response, and the characteristics of lymphokine-induced microbicidal and microbistatic processes. These organisms each enter the macrophage by endocytosis, but they then reside at different sites in relation to the phagolysosomal system. The basis of obligate parasitism remains unknown; however, both the protozoa and the host cell have important effects on the function of the other during parasitism. The macrophage may play a pivotal role in the immunosuppression associated with the early stages of infection by each of these microbes. Genetic influences on the response to infection have been clearly identified in murine models. Lymphocyte products from immune cells have marked effects on the interactions of protozoa and macrophages, under some conditions stimulating protozoacidal mechanisms, and in some protozoastatic responses. The dynamic balance between protozoal parasitism and macrophage response must be further defined in order to determine the potential value of chemotherapeutic or immunologic intervention.

Role of membranes of mycelial Mucor rouxii in synthesis and secretion of cell wall matrix polymers

Membrane fractions of the mycelial form of Mucor rouxii contained endogenous polyuronides and glycoproteins with sugar compositions similar to the cell wall polyuronide (mucoran) and extracellular (wall and filtrate) glycoproteins, respectively. The polyuronide pool was rapidly labeled with D-[U-14C]glucose and on pulse-chase experiments appeared to turn over, suggesting that these polymers were precursors of the wall mucoran. In contrast, the glycoproteins appeared to accumulate. Although the membrane-associated glycoproteins had molecular weights similar to those of the extracellular glycoproteins, the bulk of the membrane-associated polyuronides were of a molecular weight lower than that of the wall polyuronide.

Three genes coding for subunits of the membrane sector (F0) of the Escherichia coli adenosine triphosphatase complex

Two mutant unc alleles, unc-469 and unc-476, have been characterized as affecting a previously undescribed gene, designated uncF. The uncF gene is part of the unc operon (with the gene order being uncBFEAGDC), although some uncertainty remains as to the relative order of the uncF and uncE genes. Mutant strains carrying the uncF469 or uncF476 allele lack the 18,000-molecular-weight component of the F0 sector of the adenosine triphosphatase in the cell membrane but retain the dicyclohexylcarbodiimide-binding protein (molecular weight, 8,400). Conversely, strains carrying mutations in the uncE gene lack the dicyclohexylcarbodiimide-binding protein but retain the 18,000-molecular-weight protein in the cell membrane. Strains carrying mutations in the uncB gene have both the 18,000-molecular-weight protein and the dicyclohexylcarbodiimide-binding protein present in the cell membranes. The three proteins of the F0 portion of the adenosine triphosphatase, viz., 24,000, 18,000, and 8,400 molecular weights, became membrane associated after in vitro transcription-translation with plasmid pAN51 as template. Plasmids carrying deletions which affected the UncBFE region were isolated from plasmid pAN51 and characterized genetically. A comparison of the genes that were absent from the various deletion plasmids with the membrane-associated products formed after in vitro transcription-translation indicated that the uncB gene coded for the 24,000-molecular-weight protein and that the gene order was probably uncBFE. A correlation between length of deoxyribonucleic acid, genes present, and their products is presented in relation to plasmid pAN51.

Cryptic operon for beta-glucoside metabolism in Escherichia coli K12: genetic evidence for a regulatory protein

Escherichia coli K12 does not metabolize beta-glucosides such as arbutin and salicin because of lack of expression of the bglBSRC operon, which contains structural genes for transport (bglC) and hydrolysis (bglB) of phospho-beta-glucosides. Mutants carrying lesions in the cis-acting regulatory site bglR metabolize beta-glucosides as a consequence of expression of this cryptic operon (Prasad and Schaefler 1974). We isolated mutations promoting beta-glucoside metabolism that were unlinked to bglR; some of these mutations were shown to be amber. All of them were mapped at 27 min on the E. coli K12 linkage map and appeared to define a single gene, for which we propose the designation bglY. Utilization of beta-glucosides in bglY mutants appeared to be a consequence of expression of the bglBSRC operon, since bglB bglR and bglB bglY double mutants had the same phenotype. All bglY mutations analyzed were recessive to the wild-type bglY+ allele. Phospho-beta-glucosidase B and beta-glucoside transport activities are inducible in bglY mutants, as they are in bglR mutants. Metabolism of beta-glucosides in both bglR and bglY mutants required cyclic AMP. We propose that bglY encodes a protein acting as a repressor of the bglBSRC operon, active in both the presence and absence of beta-glucosides, whose recognition site would be within the bglR locus.

Regulatory mutations conferring constitutive synthesis of major outer membrane proteins (OmpC and OmpF) in Escherichia coli

An ompB strain of Escherichia coli K-12 lacking major outer membrane proteins OmpC and OmpF was used to isolate a pair of mutants that have restored the ability to synthesize either OmpC or OmpF protein. These mutants were found to produce the respective proteins constitutively under the several conditions where the synthesis in the wild-type strain was markedly repressed; namely, in the absence of the ompB gene function, under restrictive medium conditions, or upon lysogenization with phage PA-2. The mutations ompCp1 and ompFp9 responsible for such synthesis were shown to be located in the close vicinity of the corresponding structural genes, ompC and ompF. Moreover, the mutations affect the expression of these genes in a cis-dominant fashion. Taken together with other evidence, it was suggested that ompCp1 and ompFp9 represent regulatory site mutations occurring at the promoter regions of ompC and ompF respectively. Relevance of these findings to the genetic control of outer membrane protein synthesis is discussed.

Conditional lethality of Escherichia coli strains carrying dnaE and dnaQ mutations

A double mutant of Escherichia coli K12 which carries a conditional lethal mutator mutation, dnaQ49 (Horiuchi et al. 1978), and a DNA polymerase III-deficient mutation, dnaE486 (Wechsler and Gross 1971), was found to be more thermolabile than was either of the dnaQ49 or dnaE486 single mutants. The double mutant is able to grow at 28 degrees C but not at 30 degrees C. Under the restrictive conditions DNA synthesis, but not protein synthesis, of the double mutant was suppressed. All the other combinations of dnaQ and dnaE mutation alleles tested so far rendered the cells thermolabile. A dnaZ mutation exerted a similar effect on the dnaQ strain. However, when non-specific temperature-sensitive growth mutations were combined with the dnaQ49 mutation, no such increase in thermosensitivity was observed. There is a possibility that the product of the dnaQ gene interacts directly with the DNA replicating enzyme complex.

Two interacting mutations causing temperature-sensitive phosphatidylglycerol synthesis in Escherichia coli membranes

A conditionally lethal mutant of Escherichia coli lacking phosphatidylglycerol in vivo at 42 degrees C has been previously isolated by two-stage mutagenesis (M. Nishijima and C. R. H. Raetz, J. Biol. Chem. 254:7837-7844, 1979). In the first step (designated pgsA444) the phosphatidylglycerophosphate synthetase is partially inactivated, but the resulting strain continues to make about two-thirds of the normal level of phosphatidylglycerol and is not temperature sensitive. The second lesion, termed pgsB1, causes temperature-sensitive growth and phosphatidylglycerol synthesis in strains harboring pgsA444. The pgsA locus appears to be the structural gene for the synthetase and maps near min 42. In the present study we mapped the pgsB1 mutation and characterized its interaction with pgsA444 by genetic and biochemical methods. Unexpectedly, pgsB1 was not a second lesion in the pgsA structural gene, but rather mapped at a distinct site near minute 4. P1 vir-mediated contransduction suggested the gene order pantonA-dapD-pgsB-dnaE (clockwise). Independent evidence for the genetic mapping was provided by the identification of two hybrid ColE1 plasmids (pLC26-43 and pLC34-20. L. Clarke and J. Carbon, Cell 9:91-99, 1976) which both carry pgsB+ and dnaE+. Introduction of either the pgsA+ or the pgsB+ gene (via episomes, hybrid plasmids or P1 vir transduction) suppressed the temperature sensitivity of the double mutant (pgsA444 pgsB1) and restored normal levels of phosphatidylglycerol at 42 degrees C. In addition, strains with the pgsA+ pgsB1 genotype produced a novel lipid (X) at all temperatures, whereas the double mutant (pgsA444 pgsB1) contained two unusual lipids (X and Y) after 3 h at 42 degrees C. Both X and Y are precursors of lipopolysaccharide, and introduction of pgsB+ into the double mutant caused the disappearance of X and Y. Although the biochemical basis of the pgsB1 lesion is unknown, its existence suggests a previously unrecognized link between lipopolysaccharide and phosphatidylglycerol syntheses in E. coli.

Determination of the functions of hemolytic plasmid pHly152 of Escherichia coli

The alpha-hemolytic Escherichia coli strain PM152 harbors three transmissible plasmids, which have molecular weights of 65 X 10(6) (pA152), 41 X 10(6) pHly152), and 32 X 10(6) (pC152). Plasmids pHly152 and pC152 belong to incompatibility groups J2 and N, respectively. By transforming E. coli K-12 with isolated plasmids, we showed that the genetic determinant required for hemolysis was located entirely on plasmid pHly152, and a physical map of this plasmid was constructed. By transposon mutagenesis, a deoxyribonucleic acid segment of about 3.5 X 10(6) daltons was identified as being essential for hemolysis. Most of the EcoRI and HindIII fragments of the hemolytic plasmid pHly152 were cloned by using pACYC184 and RSF2124 as vectors. Two classes of Tn3-induced hemolysis-negative mutants could be complemented by recombinant plasmids carrying fragments from the hemolysis region of pHly152, whereas a third class could be restored to hemolytic activity only by recombination between the mutant plasmids and a suitable recombinant deoxyribonucleic acid. These data suggest that there are at least three clustered cistrons which are required for hemolysis. Other EcoRI and HindIII fragments of pHly152 were identified as being essential for replication, incompatibility, transfer, and restriction.

Molecular cloning of Escherichia coli K-12 hexuronate system genes: exu region

Lambda transducing bacteriophages carrying the exu region (min 66) of Escherichia coli K-12 (lambda pexu) were previously isolated. A restriction map of these phages is presented. Starting from the lambda pexu phage deoxyribonucleic acid, various endonuclease-generated exu fragments were subcloned into multicopy plasmid vectors, using in vitro recombination techniques. The precise location of the exu genes, relative to the endonuclease sites, was determined. Plasmids carrying uxaC and uxaA genes overproduced the corresponding enzymes 30- to 40-fold. When these plasmids were expressed in an in vitro protein-synthesizing system, two polypeptides of 50,500 and 53,000 molecular weights appeared and were identified as the uxaC and uxaA gene products. A 2.6-kilobase-pair deoxyribonucleic acid fragment was shown to code for a functional exuR repressor which controls the expression of the exu region. Plasmids containing this fragment overproduced the regulatory protein. It was possible to localize the operator region, uxaCo, which overlapped a PstI endonuclease site, and to confirm the transcriptional direction of the uxaC-uxaA operon from uxaC to uxaA.

Coenzyme M derivatives and their effects on methane formation from carbon dioxide and methanol by cell extracts of Methanosarcina barkeri

Extracts of Methanosarcina barkeri reduced methanol and CO2 to CH4 in the presence of H2 and converted methanol stoichiometrically into CH4 and CO2 in the absence of H2. In dialyzed cell-free extracts these reactions were stimulated by 2-mercaptoethanesulfonic acid (coenzyme M) and some derivatives (acetyl and formylcoenzyme M and the oxidized form of coenzyme M), which could be converted to coenzyme M by enzyme systems present in the extracts. Methylcoenzyme M could not be used in these systems.

Vectorial and nonvectorial transphosphorylation catalyzed by enzymes II of the bacterial phosphotransferase system

Vectorial transphosphorylation of hexitols, catalyzed by enzymes II of the bacterial phosphotransferase system, was studied in intact cells and membrane vesicles of Escherichia coli. In strains depleted of phosphoenolpyruvate and unable to metabolize the internal hexitol phosphate, internal mannitol-1-phosphate stimulated uptake of extracellular [14C]mannitol, whereas external mannitol stimulated release of [14C]mannitol from the intracellular [14C]mannitol-1-phosphate pool. The stoichiometry of mannitol uptake to mannitol release was 1:1. Glucitol did not promote release of [14C]mannitol from the mannitol phosphate pool but stimulated release of [14C]glucitol from internal glucitol phosphate pools when the glucitol enzyme II was induced to high levels. In E coli cells and membrane vesicles, both vectorial and nonvectorial transphosphorylation reactions of hexitols and hexoses were demonstrated. The nonvectorial reactions, but not the vectorial reactions, catalyzed by the mannitol and glucose enzymes II, were inhibited by p-chloromercuriphenyl sulfonate, a membrane-impermeable sulfhydryl reagent which inactivates enzymes II. Similarly, glucose-6-sulfate, an inhibitor of the glucose enzyme II-catalyzed transphosphorylation reaction, specifically inhibited the nonvectorial reaction. This compound was shown to be a noncompetitive inhibitor of methyl alpha-glucoside phosphorylation employing phospho-HPr as the phosphate donor. It apparently exerts its inhibitory effect by exclusive binding to the sugar phosphate binding site on the enzyme II complex. The results are consistent with the conclusion that enzymes II can exist in two distinct dispositions in the membrane, one of which catalyzes vectorial transphosphorylation, and the other catalyzes nonvectorial transphosphorylation.

Ferric citrate transport in Escherichia coli requires outer membrane receptor protein fecA

Mutants of Escherichia coli K-12 AB2847 and of E. coli K-12 AN92 were isolated which were unable to grow on ferric citrate as the sole iron source. Of 22 mutants, 6 lacked an outer membrane protein, designated FecA protein, which was expressed by growing cells in the presence of 1 mM citrate. Outer membranes showed an enhanced binding of radioactive iron, supplied as a citrate complex, depending on the amount of FecA protein. The FecA protein was the most resistant of the proteins involved in ferric irion iron translocation across the outer membrane (FhuA = TonA, FepA, Cir, or 83K proteins) to the action of pronase P. It is also shown that previously isolated fec mutants (G. C. Woodrow et al., J. Bacteriol. 133:1524-1526, 1978) which are cotransducible with argF all lack the FecA protein. They were termed fecA to distinguish them from the other ferric citrate transport mutants, now designated fecB, which mapped in the same gene region at 7 min but were not cotransducible with ArgF. E. coli W83-24 and Salmonella typhimurium, which are devoid of a citrate-dependent iron transport system, lacked the FecA protein. It is proposed that the FecA protein participates in the transport of ferric citrate.

Biological reactivity of hypochlorous acid: implications for microbicidal mechanisms of leukocyte myeloperoxidase

Oxidative degradation of biological substrates by hypochlorous acid has been examined under reaction conditions similar to those found in active phagosomes. Iron sulfur proteins are bleached extremely rapidly, followed in decreasing order by beta-carotene, nucleotides, porphyrins, and heme proteins. Enzymes containing essential cysteine molecules are inactivated with an effectiveness that roughly parallels the nucleophilic reactivities of their sulfhydryl groups. Other compounds, including glucosamines, quinones, riboflavin, and, except for N-chlorination, phospholipids, are unreactive. Rapid irreversible oxidation of cytochromes, adenine nucleotides, and carotene pigments occurs when bacterial cells are exposed to exogenous hypochlorous acid; with Escherichia coli, titrimetric oxidation of cytochrome was found to coincide with loss of aerobic respiration. The occurrence of these cellular reactions implicates hypochlorous acid as a primary microbicide in myeloperoxidase-containing leukocytes; the reactivity patterns observed are consistent with the view that bactericidal action results primarily from loss of energy-linked respiration due to destruction of cellular electron transport chains and the adenine nucleotide pool.

Formation of a lambda (Tn10) tyrR+ specialized transducing bacteriophage from Escherichia coli K-12

The transposon Tn10, coding for resistance to tetracycline, was inserted close to the tyrR+ gene at min 28 on the Escherichia coli chromosome. The homology between this transposon and a lambda (Tn10) phage was employed to direct integration of lambda close to tyrR+ with subsequent isolation of a lambda (Tn10) tyrR+ transducing phage. Results of restriction endonuclease analysis of the transducing phage are presented.

Plasmid replication functions: two distinct segments of plasmid R1, RepA and RepD, express incompatibility and are capable of autonomous replication

The genetic determinants for replication and incompatibility of plasmid R1 were investigated by gene cloning methods, and three types of R1 miniplasmid derivatives were generated. The first, exemplified by plasmid pKT300, consisted of a single BglII endonuclease-generated deoxyribonucleic acid fragment derived from the R1 region that is located between the determinants for conjugal transfer and antibiotic resistance. Two types of miniplasmids could be formed from PstI endonuclease-generated fragments of pKT300. One of these, which is equivalent to miniplasmids previously generated from plasmids R1-19 and R1-19B2, consisted of two adjacent PstI fragments that encode the RepA replication system of plasmid R1. The other type contained a segment of R1, designated the RepD replication region, that is adjacent to the RepA region and that has not been identified previously as having the capacity for autonomous replication. Plasmid R1, therefore, contained two distinct deoxyribonucleic acid segments capable of autonomous replication. The RepA-RepD miniplasmid pKT300 had a copy number about eightfold higher than that of R1 and hence lacked a determinant for the regulation of plasmid copy number. Like R1, it was maintained stably in dividing bacteria. RepA miniplasmids had copy numbers which were two- to fourfold higher than that of R1 (i.e., which were lower than that of pKT300) and were maintained slightly less stably than those of pKT300 and R1. The RepD miniplasmid was not maintained stably in dividing bacteria. Previous experiments have shown that incompatibility of IncFII group plasmids is specified by a plasmid copy control gene. Despite the fact that RepA miniplasmids of R1 were defective in copy control, they nevertheless expressed incompatibility. This suggests that two genes are responsible for plasmid copy control, one that specifies incompatibility and is located on RepA miniplasmids and another that is located outside of, but adjacent to, the RepA replication region. Hybrid plasmids composed of pBR322 and one PstI fragment from the RepA region, P-8, exhibited incompatibility towards R2 and RepA miniplasmids but not the RepD miniplasmid, whereas hybrids composed of pBR322 and the PstI fragment of the RepD region, P-3, exhibited incompatibility towards R1 and the RepD miniplasmid but not RepA miniplasmids. These results indicate that the two replication systems are functionally distinct and that, although the RepA system is the principal replication system of R1, the RepD system also plays a role in the maintenance of this plasmid.

Isolation and characterization of a Pseudomonas aeruginosa mutant producing a nontoxic, immunologically crossreactive toxin A protein

Nitrosoguanidine mutagenesis of Pseudomonas aeruginosa strain PAO-1 yielded a mutant strain, PAO-PR1, which produced a protein that was immunologically indistinguishable from native toxin A and was nontoxic for cultured Chinese hamster ovary cells. In contrast to native toxin, the cell-associated and extracellular crossreactive material (CRM), designated "CRM protein," possessed no adenosine diphosphate-ribosylating activity. This CRM protein comigrated with native toxin A on sodium dodecyl sulfate/polyacrylamide gels, could be immunoprecipitated with antitoxin from culture supernatants of strain PAO-PR1, and gave a reaction of identity in immunological assays. Equivalent amounts of toxin A antigen and CRM protein antigen were produced in liquid culture by their respective strains as quantitated in a radioimmunoassay for toxin A. These data suggest that mutant strain PAO-PR1 possesses one or more missense mutations within the structural gene for toxin A that adversely affect enzymatic activity, thereby rendering the molecule nontoxic.

Deletion of the penicillin-binding protein 5 gene of Escherichia coli

A strain of Escherichia coli that has a deletion of the entire dacA gene has been constructed. The complete lack of penicillin-binding protein 5 in this strain establishes that the activity of this protein is not essential for the growth of E. coli.

Enzymological basis for growth inhibition by L-phenylalanine in the cyanobacterium Synechocystis sp. 29108

The pattern of allosteric control in the biosynthetic pathway for aromatic amino acids provides a basis to explain vulnerability to growth inhibition by l-phenylalanine (0.2 mM or greater) in the unicellular cyanobacterium Synechocystis sp. 29108. We attribute growth inhibition to the hypersensitivity of 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase to feedback inhibition by l-phenylalanine. Hyperregulation of this initial enzyme of aromatic biosynthesis depletes the supply of precursors needed for biosynthesis of l-tyrosine and l-tryptophan. Consistent with this mechanism is the total reversal of phenylalanine inhibition by a combination of tyrosine and tryptophan. Inhibited cultures also contained decreased levels of phycocyanin pigments, a characteristic previously correlated with amino acid starvation in cyanobacteria. l-Phenylalanine is a potent noncompetitive inhibitor (with both substrates) of 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase, whereas l-tyrosine is a very weak inhibitor. Prephenate dehydratase also displays allosteric sensitivity to phenylalanine (inhibition) and to tyrosine (activation). Both 2-fluoro and 4-fluoro derivatives of phenylalanine were potent analog antimetabolites, and these were used in addition to l-phenylalanine as selective agents for resistant mutants. Mutants were isolated which excreted both phenylalanine and tyrosine, the consequence of an altered 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase no longer sensitive to feedback inhibition. Simultaneous insensitivity to l-tyrosine suggests that l-tyrosine acts as a weak analog mimic of l-phenylalanine at a common binding site. Prephenate dehydratase in the regulatory mutants was unaltered. Surprisingly, in view of the lack of regulation in the tyrosine branchlet of the pathway, such mutants excrete more phenylalanine than tyrosine, indicating that l-tyrosine activation dominates l-phenylalanine inhibition of prephenate dehydratase in vivo. In mutant Phe r19 the loss in allosteric sensitivity of 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase was accompanied by a threefold increase in specific activity. This could suggest that existence of a modest degree of repression control (autogenous) over 3-deoxy-d-arabinoheptulosonate synthase, although other explanations are possible. Specific activities of chorismate mutase, prephenate dehydratase, shikimate/nicotinamide adenine dinucleotide phosphate dehydrogenase, and arogenate/nicotinamide adenine dinucleotide phosphate dehydrogenase in mutant Phe r19 were identical with those of the wild type.

Persistent in vitro interaction of virulent and attenuated canine distemper virus with bovine cells

Bovine macrophage and non-macrophage cultures were infected with either virulent or attenuated canine distemper virus (CDV). Macrophages were resistant to virulent CDV; however, they supported growth of the attenuated virus. Non-macrophage cultures supported growth of both virus variants in a persistent, non-lytic manner. Major differences between these two systems of in vitro viral persistence were seen in the host cell spectrum of progeny virus and the outcome of cocultivation experiments with Vero cells. Results obtained indicate that in vivo virulence of CDV is not linked to maturation in a macrophage, but rather, propagation in a given cell culture system results in selective growth of virulent or attenuated viral mutants. It is further concluded that in vivo virulence and in vitro growth potential of CDV are disparate properties of the virion.

The nucleotide sequence of the cloned tufA gene of Escherichia coli

The 4 kb (8.5 % lambda units) EcoRI fragment harboring the tufA gene of Escherichia coli was cloned using plasmid pTUA1 (Shibuya et al., 1979) and its structure was analyzed. The nucleotide sequence of about 1500 base pairs, covering the C-terminal portion of elongation factor EF-G (fus gene), the intercistronic region between fus and tufA, the entire structural gene for tufA with the GUG initiation and UAA termination codons, and the 3' flanking region of tufA, was determined. Comparison of the tufA nucleotide sequence with the tufB sequence (An and Friesen, 1980) and the known amino acid sequence of EF-Tu (Arai et al., 1980) revealed that the products of genes tufA and tufB are identical except for one amino acid at the C-terminal, i.e., glycine for tufA and serine for tufB. Nucleotide differences between tufA and tufB were found at 13 positions. Among them, one in the initiation codon and the other one in the C-terminal amino acid codon had replacements at the first letter of the codons. The other eleven changes were in the third codon positions, which did not affect the amino acid coding. The pattern of codon usage in tufA and tufB is highly nonrandom, and remarkably similar to that in ribosomal protein genes, with the codons for the most abundant species of isoaccepting tRNAs being preferentially utilized (Post et al., 1979; Post and Nomura, 1980).

Nucleotide sequence and expression of Escherichia coli trpR, the structural gene for the trp aporepressor

The nucleotide sequence of trpR of Escherichia coli was determined. This gene codes for a polypeptide (Mr 12,356) that is 108 amino acid residues in length. NH2-terminal, COOH-terminal, and total amino acid analyses of purified aporepressor agree with the deduced amino acid sequence and establish the translation start and stop codons of the structural gene. The transcription start site for trpR mRNA synthesis in vitro was shown to be 56 base pairs prior to the translation start site. The nucleotide sequence on either side of the transcription start site is homologous to the trp operon operator. Purified trp aporepressor, when activated by L-tryptophan, protects restriction sites in this region, the presumed trpR operator, from cleavage by the respective restriction endonucleases. Bound RNA polymerase protects the same restriction sites. These findings and the additional observation that trp repressor inhibits transcription initiation in vitro establish that there is a functional overlap of operator and promoter sequences in the regulatory region of the trpR operon. These findings indicate that expression of trpR is autoregulatory.

Rifampin as a selective agent for isolation of oral spirochetes

Spirochetes indigenous to the healthy gingival crevice of the human mouth were isolated directly from colonies in agar medium containing rifampin as a selective agent.

Temperature-sensitive glutamate dehydrogenase mutants of Salmonella typhimurium

Mutants of Salmonella typhimurium defective in glutamate dehydrogenase activity were isolated in parent strains lacking glutamate synthase activity by localizcd mutagenesis or by a general mutagenesis combined with a cycloserine enrichment for glutamate auxotrophs. Two mutants with temperature-sensitive phenotypes had glutamate dehydrogenase activities that were more thermolabile than that of an isogenic control strain. Eight other mutants had less than 10% of the wild-type glutamate dehydrogenase activity. All the mutations were cotransducible with a Tn10 element (zed-2:Tn10) located at approximately 23 U on the S. typhimurium linkage map. These data strongly indicate that this region contains the structural gene (gdhA) for glutamate dehydrogenase.

The ebg operon consists of at least two genes

The ebg operon of Escherichia coli includes a second gene designated ebgB. The ebgB gene product is a 79,000-molecular-weight protein and is expressed coordinately with the ebgA gene product, ebg beta-galactosidase. Insertion of the transposable elements Tn5 and Tn9 into ebgA eliminates the expression of ebgB, suggesting that ebgB is distal to ebgA. Ultraviolet light mapping confirms that gene order. The function of the ebgB gene product is unknown.

Construction of an Escherichia coli strain unable to synthesize putrescine, spermidine, or cadaverine: characterization of two genes controlling lysine decarboxylase

We have previously described a polyamine-deficient strain of Escherichia coli that contained deletions in speA (arginine decarboxylase), speB (agmatine ureohydrolase), speC (ornithine decarboxylase), and speD (adenosylmethionine decarboxylase). Although this strain completely lacked putrescine and spermidine, it was still able to grow at a slow rate indefinitely on amine-deficient media. However, these cells contained some cadaverine (1,5-diaminopentane). To rule out the possibility that the presence of cadaverine permitted the growth of this strain, we isolated a mutant (cadA) that is deficient in cadaverine biosynthesis, namely, a mutant lacking lysine decarboxylase, and transduced this cadA gene into the delta (speA-speB) delta speC delta D strain. The resultant strain had essentially no cadaverine but showed the same phenotypic characteristics as the parent. Thus, these results confirm our previous findings that the polyamines are not essential for the growth of E. coli or for the replication of bacteriophages T4 and T7. We have mapped the cadA gene at 92 min; the gene order is mel cadA groE ampA purA. A regulatory gene for lysine decarboxylase (cadR) was also obtained and mapped at 46 min; the gene order is his cdd cadR fpk gyrA.

Selective neutrality of 6PGD allozymes in E. coli and the effects of genetic background

We have used gluconate-limited chemostats to study selective differences between isogenic strains of Escherichia coli K12 into which four naturally occurring alleles coding for allozymes of 6-phosphogluconate dehydrogenase (6PGD) had been transferred. The limit of detectability of selection with our procedures is a selection coefficient of 0.5%. In the normal E. coli K12 genetic background, all alleles are selectively neutral or nearly neutral. The absence of detectable selection does, however, depend on genetic background and on such environmental factors as cell density. In a genetic background containing a mutation that cuts off the alternative metabolic route for 6-phosphogluconate, selection between allozymes can be detected, and the selection is in the direction expected from the measured apparent Km values of the allozymes. Even when the alternative metabolic route is not blocked by mutation, one of the 6PGD allozymes has a detrimental, but density-dependent, interaction with a mutation conferring resistance to bacteriophage T5. In all cases, the observed selection is due to the allozymes themselves (or to associated regulatory elements), as the selection disappears when the chemostats are limited by a different carbon source (ribose plus succinate). Nevertheless, the four alleles do seem to be selectively neutral or nearly neutral in the normal E. coli K12 genetic background. Moreover, the distribution of allele frequencies in natural populations of E. coli is in accord with the expectations of selective neutrality.