Linkage map of Salmonella typhimurium, edition IV

Suppressor Mutants: History and Today's Applications

For decades, biologist have exploited the near boundless advantages that molecular and genetic tools and analysis provide for our ability to understand biological systems. One of these genetic tools, suppressor analysis, has proven invaluable in furthering our understanding of biological processes and pathways and in discovering unknown interactions between genes and gene products. The power of suppressor analysis lies in its ability to discover genetic interactions in an unbiased manner, often leading to surprising discoveries. With advancements in technology, high-throughput approaches have aided in large-scale identification of suppressors and have helped provide insight into the core functional mechanisms through which suppressors act. In this review, we examine some of the fundamental discoveries that have been made possible through analysis of suppressor mutations. In addition, we cover the different types of suppressor mutants that can be isolated and the biological insights afforded by each type. Moreover, we provide considerations for the design of experiments to isolate suppressor mutants and for strategies to identify intergenic suppressor mutations. Finally, we provide guidance and example protocols for the isolation and mapping of suppressor mutants.

De novo pyrimidine synthesis is necessary for intestinal colonization of Salmonella Typhimurium in chicks

pyrE (STM3733) encodes orotate phosphoribosyltransferase (OPRTase; EC 2.4.2.10), the fifth enzyme of the de novo pyrimidine biosynthetic pathway. We identified a ΔpyrE mutant as under selection in screening of a Salmonella mutant library in 4-day old chicks. Here, we confirm that a ΔpyrE mutant colonizes 4-day old chicks poorly in competitive infection with isogenic wild type, and that the ability of this mutant to colonize chicks could be restored by providing a copy of pyrE in trans. We further show that our ΔpyrE mutant grows poorly in nutrient poor conditions in vitro, and that the ability of this mutant to grow is restored, both in vitro and in chicks, when precursors to the pyrimidine salvage pathway were provided. This finding suggests that the environment in the chick intestine during our infections lacks sufficient precursors of the pyrimidine salvage pathway to support Salmonella growth. Finally, we show that the colonization defect of a ΔpyrE mutant during infection occurs in to chicks, but not in CBA/J mice or ligated ileal loops in calves. Our data suggest that de novo pyrimidine synthesis is necessary for colonization of Salmonella Typhimurium in the chick, and that the salvage pathway is not used in this niche.

Microbial models and regulatory elements in the control of purine metabolism

Bacterial systems have been used to identify and characterize the organization of the genetic units and the regulatory elements that control purine metabolism. An analysis of 13 genes that control the biosynthesis of AMP and GMP has revealed three multigenic operons. These show properties of gene contiguity, promoter sites, coordinate expression and polarity effects. The unit controlling the formation of IMP is one operon (pur JHD) consisting of three genes which together control the formation of phosphoribosylglycinamide synthetase (EC 6.3.4.13), an early enzyme in the biosynthetic pathway, and a terminal bifunctional complex (IMP cyclohydrolase--formyltransferase). Regulatory mutants were isolated and characterized by several methods including the use of a unique fusion of two unrelated operons. Both operator constitutive and repressor type (purR) mutations have been identified. The purR product functions in the common control of several genetically distinct enzymes that participate before the formation of IMP. Plasmid DNA enriched for the purE operon has been isolated and used in the study of the role of nucleotide effectors in the binding of repressor-like proteins. AMP but not GMP is needed for binding, and purR mutants are deficient in the binding substance. Mutants with differential blocks in the salvage and interconverting reactions have been used to characterize the regulatory elements of the formation and the activity of guanosine kinase, GMP reductase (EC 1.6.6.8), and purine nucleoside phosphorylase (EC 2.4.2.1). Two structural gene products (purF) and (purG) have been implicated as possible regulatory elements for the use of guanosine, and a role for glutamine in the induction of GMP reductase has been revealed.

Insensitivity of D-amino acid dehydrogenase synthesis to catabolic repression in dadR mutants of Salmonella typhimurium

It has been found that synthesis of D-amino acid dehydrogenase in Salmonella typhimurium is stimulated by cyclic AMP and crp gene product. This indicates that catabolic control of the dehydrogenase resembles other bacterial systems of catabolic repression. We have isolated S. typhimurium mutants, dadR, which are resistant to L-methionine-interference with D-histidine utilization and are able to utilize D-tryptophan as a precursor of L-tryptophan. Mapping data indicate that the dadR locus is closely linked to dadA coding for the structure of D-amino acid dehydrogenase. The synthesis of the dehydrogenase in dadR mutants is completely insensitive to the repression by glucose, but remains inducible by L-alanine. We conclude thereof that dadR mutants have changes in the promoter region which increase the expression of the dadA gene in the presence of glucose metabolism. A likely possibility that induction of the dad operon by alanine might be under positive control is discussed.

Molecular cloning and characterization of the pyrB gene of Lactobacillus leichmannii encoding aspartate transcarbamylase

The Lactobacillus leichmannii pyrB gene, encoding pyrimidine biosynthetic enzyme aspartate transcarbamylase (ATCase), was cloned from a partial genomic library lying on a 1468 bp Sa/I/BstXI fragment. The predicted polypeptide sequence extending over 351 amino acid residues (M(r) 39 855 Da) was compared to those of various other organisms revealing clear identities towards them and important conservative stretches, implying that these proteins are closely related. Transcriptional initiation was mapped by primer extension and occurred 54 bp upstream of the pyrB open reading frame (ORF). Northern blot analysis indicates that the pyrB gene is transcribed as a single mRNA and not together with the following overlapping pyrC gene as a bicistronic mRNA. At high copy number the pyrB gene of L leichmannii seems to be lethal for its E coli host; inserted in a low copy vector it complements the uracil auxotrophy of an E coli pyrB mutant which shows distinct ATCase activity in the cell extract. With an excess of uracil in the growth medium the gene is apparently repressed and no ATCase activity can be measured.

Identification and characterization of a relA-dependent starvation-inducible locus (sin) in Salmonella typhimurium

By use of Mu cts d1(Ap lac) phage, a strain of Salmonella typhimurium was isolated containing a Mu d insertion in a locus (sinA) which is induced during nicotinate, thiamine, purine, amino acid, phosphate, and carbon starvation conditions. Depending on the starvation condition, a 2- to 10-fold increase in beta-galactosidase activity was demonstrated. The sinA locus, which mapped at 32 U, became induced after a decline in growth rate due to starvation. The introduction of relA into the sinA-lac strain prevented induction by nicotinate starvation and partially prevented induction by phosphate starvation. The data suggest that sinA responds to changes in growth rate due to various nutrient starvation conditions and probably responds in part to changes in guanosine tetraphosphate levels.

Hydrophobic peptide auxotrophy in Salmonella typhimurium

The growth of a pleiotropic membrane mutant of Salmonella typhimurium with modified lipopolysaccharide composition was found to be strictly dependent on the peptone component of complex media. Nutritional Shiftdown into minimal media allowed growth for three to four generations. Of 20 commercial peptones, only enzymatic digests supported growth to varying degrees. Neither trace cations, amino acids, vitamins, carbohydrates, lipids, glutathione, polyamines, carbodimides, nor synthetic peptides stimulated growth; however, cells still metabolized carbohydrates, and amino acid transport systems were shown to be functional. A tryptic digest of casein was fractionated into four electrophoretically different peptide fractions of 1,000 to 1,200 molecular weight which supported growth to varying degrees. The best of these was further fractionated to two highly hydrophopic peptides. N-terminal modifications eliminated biological activity. Fluorescein-conjugated goat antibody to rabbit immunoglobulin G was used as a probe to detect antipeptide antibody-peptide complexes on membrane preparations. Cells grown on peptone distributed the peptide into both inner and outer membranes. The peptide could be removed with chaotropic agents, and cells had to be pregrown in peptone-containing media to bind the hydrophobic peptide. The gene (hyp) responsible for peptide auxotrophy was mapped at 44 to 45 units by conjugation.

Ubiquinone synthetic pathway in flagellation of Salmonella typhimurium

Flagellation of Salmonella typhimurium was found to require a functional pathway for ubiquinone synthesis as well as growth in the presence of aliphatic or aromatic carboxylic acids. Selection for constitutive flagellation eliminated the requirement for growth in the presence of added carboxylic acids.

Deletion of a ribosomal ribonucleic acid operon in Escherichia coli

One (rrnE) of the seven operons which codes for ribosomal ribonucleic acid in Escherichia coli was deleted. No significant change in phenotype was observed even under maximum laboratory growth conditions.

Salmonella typhimurium mutants with altered glutamate dehydrogenase and glutamate synthase activities

Although glutamate is a key compound in nitrogen metabolism, little is known about the function or regulation of its two biosynthetic enzymes, glutamate dehydrogenase and glutamate synthase. To begin the characterization of glutamate formation in Salmonella typhimurium, we isolated mutants having altered glutamate dehydrogenase and glutamate synthase activities. Mutants which failed to grow on media with glucose as the carbon source and less than 1 mM (NH(4))(2)SO(4) as the nitrogen source (Asm(-)) had about one-fourth the normal glutamate synthase activity and one-half the glutamine synthetase activity. The asm mutations also prevented growth with alanine, arginine, or proline as nitrogen sources and conferred resistance to methionine sulfoximine. When a mutation (gdh-51) causing the loss of glutamate dehydrogenase activity was transferred into a strain with an asm-102 mutation, the resulting asm-102 gdh-51 mutant had a partial requirement for glutamate. A strain isolated as a complete glutamate auxotroph had a third mutation, in addition to the asm-102 gdh-51 lesions, that further decreased the glutamate synthase activities to 1/20 the normal level. Both the asm-102 and gdh-51 mutations were located on the S. typhimurium linkage map at sites distinct from those found for mutations causing similar phenotypes in Klebsiella aerogenes and Escherichia coli.

Order of genes near nif in Klebsiella pneumoniae

Analysis of strains with deletions of all or part of nif have ordered the Klebsiella pneumoniae genetic loci as thi rbt dal udk gnd rfb has nif shiA. The his-nif plasmids pRD1 and pTM4010 contain the genes gnd rfb his nif shiA.

Bacterial DNA synthesized under phage control in a DNA-defective Salmonella-mutant and packaged into a special fraction of transducing particles of phage P22

Lysates of P22 contain a small fraction of transducing particles with bacterial DNA replicated semiconservatively after the time of infection. It was demonstrated that the presence and relative amount of this class of transducing particles was unchanged, if infection of Salmonella occured under a condition nonpermissive for bacterial DNA replication. Analysis of particles with DNA fragments derived from different regions of the Salmonella chromosome indicated that the replication of the bacterial DNA carried by these transducing particles was not initiated specifically at the normal origin for bacterial chromosome replication.

Pyridine nucleotide cycle of Salmonella typhimurium: isolation and characterization of pncA, pncB, and pncC mutants and utilization of exogenous nicotinamide adenine dinucleotide

Mutants of Salmonella typhimurium LT-2 deficient in nicotinamidase activity (pncA) or nicotinic acid phosphoribosyltransferase activity (pncB) were isolated as resistant to analogs of nicotinic acid and nicotinamide. Information obtained from interrupted mating experiments placed the pncA gene at 27 units and the pncB gene at 25 units on the S. typhimurium LT-2 linkage map. A major difference in the location of the pncA gene was found between the S. typhimurium and Escherichia coli linkage maps. The pncA gene is located in a region in which there is a major inversion of the gene order in S. typhimurium as compared to that in E. coli. Growth experiments using double mutants blocked in the de novo pathway to nicotinamide adenine dinucleotide (NAD) (nad) and in the pyridine nucleotide cycle (pnc) at either the pncA or pncB locus, or both, have provided evidence for the existence of an alternate recycling pathway in this organism. Mutants lacking this alternate cycle, pncC, have been isolated and mapped via cotransduction at 0 units. Utilization of exogenous NAD was examined through the use of [14C]carbonyl-labeled NAD and [14C]adenine-labeled NAD. The results of these experiments suggest that NAD is degraded to nicotinamide mononucleotide at the cell surface. A portion of this extracellular nicotinamide mononucleotide is then transported across the cell membrane by nicotinamide mononucleotide glycohydrolase and degraded to nicotinamide in the process. The remaining nicotinamide mononucleotide accumulates extracellularly and will support the growth of nadA pncB mutants which cannot utilize the nicotinamide resulting from the major pathway of NAD degradation. A model is presented for the utilization of exogenous NAD by S. typhimurium LT-2.

Method of isolation of cysteine constitutive mutants of the cysteine regulon in Salmonella typhimurium

A method for selection of constitutive cysB mutation is described which takes advantage of the resistance of cysteine constitutive mutants to 1,2,4-triazole. Since cysM cysK double mutants are cysteine auxotrophs, by selecting for triazole resistance in cysM strains, mutants arising under this condition also should be constitutive for cysteine biosynthesis. Genetic analysis of mutants isolated by this technique showed that their mutational sites are located in the cysB region. Biochemical assays of cysteine enzymes, sulphite reductase and O-acetylserine sulfhydrylase of the mutants showed the derepressed level of these enzymes and the lack or slight repression by 1-cysteine.

Major outer membrane protein in Salmonella typhimurium induced by maltose

A maltose-induced major outer membrane protein (the 44K protein) is demonstrated in Salmonella typhimurium. This protein resembles the lambda receptor of Escherichia coli in its location, induction properties, apparent molecular weight, and association with the peptidoglycan layer of the cell wall. The 44K protein is missing in certain Salmonella Mal- mutants, which are also missing a protein analogous to the maltose-binding protein of E. coli. Thus, these mutants may be defective in the control of maltose genese in Salmonella. The proteins appear to be closely related, as indicated by cross-reaction of the Salmonella protein with the antiserum raised against the lambda receptor; however, they are not identical, since the peptide patterns obtained after limited proteolysis are completely different. Bacteriophage lambda does not use the 44K protein as a receptor.

Mapping of the hemE locus in Salmonella typhimurium

A new type of heme-deficient mutant was isolated in Salmonella typhimurium by neomycin selection. The mutant was deficient in uroporphyrinogen decarboxylase activity, coded by the hemE gene. The hemE gene was located between the genes rif and thi at 128 min on the chromosomal map of S. typhimurium.

Acylaminoacid esterase mutants of Salmonella typhimurium

Salmonella typhimurium contains three electrophoretically separable enzyme activities that hydrolyze N-acetyl phenylalanine beta-naphthyl ester (NAPNE). One of these enzymes is an endoprotease, protease I. Mutations at a locus apeA near purE lead to loss of this enzyme. We have found that N-acetyl leucine alpha-naphthyl ester (NALNE) is not hydrolyzed by protease I but is a good substrate for the other two activities. Using NALNE as a chromogenic substrate to screen colonies growing on agar, we have isolated mutants (apeB) that simultaneously lose both of the two other esterase activities. The chromosomal positions of apeB and nearby markers in the proC-purE region have been determined using both phage P1 and phage P22 mediated transduction. The observed order is proC thiC apeB apt apeA purE. Strains lacking all three activities (apeA apeB double mutants) have been constructed and have growth rates similar to wild-type strains.

Salmonella typhimurium mutants lacking protease II

Mutants of Salmonella typhimurium lacking protease II, an endoprotease with trypsin-like specificity, have been isolated. These mutants can be identified by using the chromogenic substrate N-methyl-N-p-toluenesulfonyl-L-lysine beta-naphthyl ester to screen colonies growing on agar for the presence of the enzyme. All of the mutations isolated map at locus tlp (typsin-like protease) which is cotransducible (approximately 1%) using phage P1 with tre (trehalose utilization) at approximately 58 min on the Salmonella map. Double mutants lacking both protease I and protease II have been constructed. These strains grew normally. They were able to degrade abnormal proteins and to carry out protein turnover during carbon starvation at the same rate as the wild type.

Genetics of Rhodospirillaceae

Images

Mutations that alter the covalent modification of glutamine synthetase in Salmonella typhimurium

glnD and glnE mutant strains of Salmonella typhimurium lack three of the four activities required for reversible covalent modification of glutamine synthetase (GS; EC 6.3.1.2). The glnD strains, which are unable to deadenylylate GS and therefore accumulate the adenylylated or less active form of the enzyme, were isolated as glutamine bradytrophs. They lack the activity of PIIA uridylyl-transferase, one of the proteins required for deadenylylation of GS; in addition, they lack PIID uridylyl-removing activity. Mutations in glnD are suppressed by second-site mutations in glnE that eliminate the activity of GS adenylyltransferase (EC 2.7.7.42) and thus prevent adenylylation of GS. The glnD and glnE strains have one-third to one-half as much total GS as the wild-type strain when they are grown in a medium containing a high concentration of NH4+. The wild-type strain derepresses synthesis of GS fourfold in response to nitrogen limitation; glnD and glnE strains derepress synthesis of the enzyme fourfold and sevenfold, respectively. Thus, mutations that alter covalent modification of GS in Salmonella do not significantly affect derepression of its synthesis. The glnD gene lies at 7 min on the Salmonella chromosome and is 50% linked to pyrH by P22-mediated transduction.

Arginine regulon control in a Salmonella typhimurium--Escherichia coli hybrid merodiploid

The regulation of synthesis of arg enzymes was studied in a hybrid merodiploid in which an episome of Escherichia coli carrying the argR+ allele was transfered to Salmonella typhimurium argR strain. The arg enzyme levels of the hybrid merodiploid were compared to that found in argR and argR+ haploids of S. typhimurium. The results showed that repression of synthesis of arg enzymes was effected through the introduction of the E. coli argR+ allele but significant quantitative differences of arg enzyme levels in the argR+ haploid and the hybrid merodiploid were observed.

Permease-specific mutations in Salmonella typhimurium and Escherichia coli that release the glycerol, maltose, melibiose, and lactose transport systems from regulation by the phosphoenolpyruvate:sugar phosphotransferase system

Several carbohydrate permease systems in Salmonella typhimurium and Escherichia coli are sensitive to regulation by the phosphoenolpyruvate:sugar phosphotransferase system. Mutant Salmonella strains were isolated in which individual transport systems had been rendered insensitive to regulation by sugar substrates of the phosphotransferase system. In one such strain, glycerol uptake was insensitive to regulation; in another, the maltose transport system was resistant to inhibition; and in a third, the regulatory mutation specifically rendered the melibiose permease insensitive to regulation. An analogous mutation in E. coli abolished inhibition of the transport of beta-galactosides via the lactose permease system. The mutations were mapped near the genes which code for the affected transport proteins. The regulatory mutations rendered utilization of the particular carbohydrates resistant to inhibition and synthesis of the corresponding catabolic enzymes partially insensitive to repressive control by sugar substrates of the phosphotransferase system. Studies of repression of beta-galactosidase synthesis in E. coli were conducted with both lactose and isopropyl beta-thiogalactoside as exogenous sources of inducer. Employing high concentrations of isopropyl beta-thiogalactoside, repression of beta-galactosidase synthesis was not altered by the lactose-specific transport regulation-resistant mutation. By contrast, the more severe repression observed with lactose as the exogenous source of inducer was partially abolished by this regulatory mutation. The results support the conclusions that several transport systems, including the lactose permease system, are subject to allosteric regulation and that inhibition of inducer uptake is a primary cause of the repression of catabolic enzyme synthesis.

Expression of Escherichia coli fol alleles in Salmonella typhimurium

Studies of the expression of Escherichia coli fol alleles in Salmonella typhimurium indicated that fol regulatory functions are highly conserved between these bacterial species.

2-deoxygalactose, a specific substrate of the Salmonella typhiimurium galactose permease: its use for the isolation of galP mutants

2-Deoxygalactose is a specific substrate of the galactose permease. The apparent Km is about 500 micron, compared to 45 micron for galactose, whereas the maximal rate of uptake is one-half to one-third of that of galactose. None of the other galactose transport systems, including methyl beta-D-thiogalactosides I and II, the beta-methyl-galactoside permease, and both arabinose systems, is able to catalyze transport of 2-deoxygalactose to a significant extent. 2-Deoxygalactose can also be used to isolate mutants defective in galactose permease, since it is bacteriostatic. Colonies that grow with lactate, malate, or succinate as a carbon source in the presence of 0.5 to 2 mM 2-doexygalactose were found to be mostly galP mutants, lacking galactose permease. Spontaneous 2-deoxygalactose-resistant strains arose with a frequency of about 2 X 10(-6). galP mutants have also been derived from pts deletion mutants that require galactose permease for growth on glucose. Revertants have been obtained that have acquired the parental phenotype.

Genetic analysis of antibiotic resistance in Streptococcus pyogenes

The genetics of antibiotic resistance in mutant strains of Streptococcus pyrogenes was studied. Utilizing a type 6 strain (9440) primarily resistant to strepttomycin (Strr), classes of mutant strains were isolated that were resistant to one of the following antibiotics: rifampin (Rifr), erythromycin (Eryr), thiostrepton (Tstr), spiramycin (Sprr), fusidic acid (Fusr), gramicidin (Grcr), ethidium bromide (Ebrr), kanamycin (Kanr), neomycin (Neor), oleandomycin (Oler), gentamicin (Genr), and novobiocin (Novr). Transduction experiments separated antibiotic resistance markers into two distinct groups: transducible markers, including Fusr, Bacr, Ksg+, Spcr, Eryr, Sprr, Rifr, Stlr, and Tstr (Bacr, Ksgr, Spcr, and Stlr refer to resistance to bacitracin, kasugamycin, spectinomycin, and streptolydigan, respectively), and nontransducible markers, including Grcr, Ebrr, Kanr, Neor, Oler, Genr, and Novr. By means of two- and three-point crosses, transducible markers (excluding tst) were located in three separate linkage groups. spr was found to be linked with ery and spc in the order spc-ery-spr, whereas in a separate linkage group the order was determined to be str-fus-bac-ksg. The third linkage group contained the rif and stl markers.

Bioautography: a general method for the visualization of isozymes

A new method has been developed for visualization of isozymes which are difficult or impossible to detect with standard histochemical or autoradiographic methods. The principle of this method, bioautography, is the use of a microbial reagent to locate an enzyme after gel electrophoresis. When bioautography was compared to other staining procedures, the bioautographic method yielded identical results to those observed by the histochemical method for lactate dehydrogenase (LDH) or by the autoradiographic method for the adenine phosphoribosyltransferase (APRT). Using the bioautographic method, stains for enzymes which could not be visualized by any other procedure have been developed: argininosuccinate lyase and branched-chain aminotransferase. By employing appropriately genetically marked bacterial strains, it should be possible to develop new isozyme stains for a large number of unstudied isozymes.

Donor strains of the soft-rot bacterium Erwinia chrysanthemi and conjugational transfer of the pectolytic capacity

Donor strains of Erwinia chrysanthemi ICPB EC16, a member of the soft-rot (pectolytic) section of the enterobacterial genus Erwinia, were obtained by chromosomal integration of an F'lac(+) plasmid originating from Escherichia coli. These stable donor strains, selected from an unstable F'lac(+) heterogenote by repeated platings of single Lac(+) colonies on lactose minimal agar, do not segregate (as does the parent F'lac(+) heterogenote) into Lac(-) or F(-) clones, in either the presence or absence of acridine orange. One representative donor strain (from the 12 that have been selected) has been examined in more detail; it can transfer ade(+), gal(+), gtu(+) (utilization of galacturonate), his(+), lac(+), leu(+), lys(+), mcu(+) (multiple carbohydrate utilization), pat(+) (production of polygalacturonic acid trans-eliminase), thr(+), and trp(+) in a polarized manner to appropriate recipient strains of E. chrysanthemi; the frequencies of ade(+), leu(+), and thr(+) transfer were higher than those of the other markers tested to date. This donor strain transfers lac(+) genes during a 6-h mating on membranes; most of the Lac(+) recombinants are donors of chromosomal markers. The kinetics of entry as well as the frequencies of transfer of chromosomal markers indicate that thr(+) and leu(+) enter the recipient as proximal markers and that lac(+) enters as a distal marker. Analysis of the recombinants demonstrates close linkage between thr and leu, ade and thr, his and pat, and his and trp loci. The results suggest that the integration of F'lac(+) into the chromosome of E. chrysanthemi has occurred at a region adjacent to the leu-thr loci, and that the chromosome is transferred in the following sequence: origin----leu--thr--ade--lys--mcu--pat--his--trp--gal--gtu--lac--F. Plant-tissue maceration occurs in Pat(+) recombinants and not in Pat(-) recombinants, even though both form another pectolytic enzyme, hydrolytic polygalacturonase. This genetic evidence supports the idea that the E. chrysanthemi polygalacturonic acid trans-eliminase plays an essential role in bringing about plant-tissue maceration.

The structure of the cysCDHIJ region in unstable cysteine or methionine requiring mutants of Salmonella typhimurium

A genetic method was devised to test the hypothesis that in some cysteine or methionine requiring (cym) mutants of Salmonella typhimurium suppression of auxotrophy is due to an insertion at the site of the cym mutation. It was found that suppressed strains have an insertion of about 9kb in the cysCDHIJ region and that in unstable suppressed strains it is the instability of this insertion which results in the segregation of cym auxotrophs.

Identification of the sid outer membrane receptor protein in Salmonella typhimurium SL1027

A protein of molecular weight 78,000 daltons, missing in albomycin and phage ES18 resistant mutants, has been identified in the outer membrane of Salmonella typhimurium SL1027. Mutants with a tonB like resistance and over production of outer membrane proteins due to iron shortage were also isolated. The mutation which leads to the protein deficiency maps in the sid gene region, the mutation related to overproduction of proteins maps near trp. Although the S. typhimurium and the E. coli protein mediate translocation of the iron complex ferrichrome and the structurally analogous antibiotic albomycin through the outer membrane no cross-reactivity exists in binding the phages T5, T1 and ES18 or colicin M.

Genetic studies on Neisseria gonorrhoeae from disseminated gonococcal infections

Isolates from uncomplicated and disseminated gonococcal infections were analyzed by using deoxyribonucleic acid-mediated transformation. Most pairs of auxotrophs could recombine, producing independent transformants. When the constellation of arginine (Arg), hypoxanthine (Hyx), and uracil (Ura) requirements was present in donor and recipient, no recombination for these traits could be detected. Except for Arg to Hyx, no linkage between Arg, Hyx, Ura, penicillin G sensitivity, and serum resistance could be demonstrated. Some distant linkage of Ura to nalidixic acid and rifampin resistances was found. The data show that the traits associated with disseminated gonococcal infection strains are not closely linked but are identical in all strains, indicating a common origin.

The genetic organization of arginine biosynthesis in Pseudomonas aeruginosa

Six loci coding for arginine biosynthetic enzymes in Pseudomonas aeruginosa strain PAO were identified by enzyme assay: argA (N-acetylglutamate synthase), argB (N-acetylglutamate 5-phosphotransferase), argC (N-acetylglutamate 5-semialdehyde dehydrogenase), argF (anabolic ornithine carbamoyl-transferase), argG (argininosuccinate synthetase), and argH (argininosuccinase). One-step mutants which had a requirement for arginine and uracil were defective in carbamoylphosphate synthase, specified by a locus designated car. To map these mutations we used the sex factor FP2 in an improved interrupted mating technique as well as the generalized transducing phages F116L and G101. We confirmed earlier studies, and found no clustering of arg and car loci. However, argA, argH, and argB were mapped on a short chromosome segment (approx. 3 min long), and argF and argG were cotransducible, but not contiguous. N-Acetylglutamate synthase, the enzyme which replenishes the cycle of acetylated intermediates in ornithine synthesis of Pseudomonas, appears to be essential for arginine synthesis since argA mutants showed no growth on unsupplemented minimal medium.

Genetic basis of Vi antigen expression in Salmonella paratyphi C

Analysis of hybrids formed in a cross between a Salmonella paratyphi C Hfr and an S. typhimurium recipient indicated that the structural genetic determinants of the S. paratyphi C Vi antigen are located closely adjacent to the mel determinant, between this marker and purA. A similar location was indicated for the structural genetic determinants of the S. typhi Vi antigen (the viaB locus) by the results of a mating in which a hybrid S. typhimurium Hfr bearing the S. typhi viaB determinants was used to transfer these genes to an S. typhimurium recipient. Mating experiments with a Vi-antigen-expressing S. typhi Hfr and an S. typhimurium hybrid recipient expressing the Vi antigen of S. paratyphi C yielded no recombinants in which loss of Vi antigen expression occurred, indicating that the chromosomal locus occupied by the genetic determinants of the S. paratyphi C Vi antigen is the same one at which, in S. typhi, the viaB genes reside. Introduction of a mutant S. typhi viaA gene into an S. typhimurium hybrid expressing the Vi antigen, as the consequence of prior receipt of the S. paratyphi C viaB determinants, resulted in that hybrid's loss of Vi antigen expression, demonstrating that the viaA determinant plays a role in Vi antigen expression in S. paratyphi C, as well as in S. typhi. Although the percentages of coinheritance of the viaB and mel determinants in the mating experiments suggested that their linkage is sufficiently close to allow cotransduction by P22, attempts to accomplish this with lysates prepared on S. typhimurium hybrids expressing either S. typhi or S. paratyphi C viaB determinants were not successful.

Ochre suppression in Salmonella typhimurium

A bacterial strain was constructed which permitted positive selection for ochre suppressor mutations as well as for the loss of suppressor function. A derivative bearing an ochre suppressor mutation was selected following mutagenesis with N-methyl-N-nitroso-N'-nitroguanidine. The suppressor-bearing strain was treated with nitrous acid to eliminate suppressor function by mutation, and a strain lacking suppressor activity was selected. The selected strain which had lost suppressor function was then subjected to mutagenesis to induce a second suppressor mutation. The alternating sequence (induction of an ochre suppressor mutation leads to induction of a mutation eliminating ochre suppressor activity) was repeated 29 and one-half times in a single strain. Some of the suppressor mutations were tentatively mapped at four locations on the chromosome. The first suppressor mutation selected maps at about minute 30 on the chromosome. The second suppressor selected maps at approximately minute 60, while the third suppressor maps nearby, possibly as far as minute 72. Among the subsequently selected suppressor mutations, all eleven which were mapped were cotransducible with the gal and nic loci near minute 36 on the chromosome and may represent more than one suppressor gene. Deletions were selected which inactivate two of the ochre suppressor alleles mapping near the gal-nic region, suggesting that one or more such genes are dispensable. Some evidence also suggests that the occurrence of either deletion mutations or transduction-mediated recombination events in the gal-nic region can cause instability of nearby suppressor alleles.

Genetics of sensitivity of Salmonella species to colicin M and bacteriophages T5, T1, and ES18

Nearly all of 62 strains of Salmonella paratyphi B were sensitive to colicin M and phage T5 but resistant to phages T1 and ES18 and to colicin B. All tested S. typhimurium strains were resistant to colicin M and phage T5, and many were sensitive to phage ES18. A rough S. typhimurium LT2 strain given the tonA region of Escherichia coli or S. paratyphi B became sensitive to colicin M and phage T5. We infer that the tonA allele of S. paratyphi B, like that of E. coli, determines an outer membrane protein that adsorbs T5 and colicin M but not phage ES18, whereas the S. typhimurium allele determines a protein able to adsorb only ES18. The partial T1 sensitivity of a rough LT2 strain with a tonA allele from E. coli or S. paratyphi B and also the tonB(+) phentotype of an E. coli B trp-tonB Delta mutant carrying an F' trp of LT2 origin showed that S. typhimurium LT2 has a tonB allele like that of E. coli with respect to determination of sensitivity to colicins and phage T1. Rough S. paratyphi B, although T5 sensitive, remained resistant to T1 even when given F' tonB(+) of E. coli origin. Classes of Salmonella mutants selected as resistant to colicin M included: T5-resistant mutants, probably tonA(-); mutants unchanged except for M resistance, perhaps tolerant; and Exb(+) mutants, producing a colicin inhibitor (presumably enterochelin). Some Exb(+) mutants were resistant to a bacteriocin inactive on E. coli but active on all tested S. paratyphi B and S. typhimurium strains (and on nearly all other tested Salmonella). A survey showed sensitivity to colicin M in several other species of Salmonella.

Chromosomal location of a structural gene for the RNA polymerase sigma factor in Escherichia coli

A set of F' strains of Escherichia coli K-12 partially diploid for various chromosomal segments has been examined for possible gene dosage effects in the synthesis of sigma factor of the DNA-dependent RNA polymerase (RNA nucleotidyltransferase; nucleoside-triphosphate:RNA nucleoti-dyltransferase, EC 2.7.7.6). It was found that all F' strains diploid for the dnaG region synthesize sigma at rates two to three times higher than other F' or F- strains. Moreover, strains of Salmonella typhimurium harboring these F' plasmids produce E. coli sigma in addition to Salmonella sigma. This has been shown on the basis of the finding that Salmonella sigma can be precipitated with antiserum against E. coli RNA polymerase but is distinguishable from E. coli sigma in its mobility in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. E. coli sigma polypeptides thus produced seem to be stable in cells of S. typhimurium. These results indicate that a structural gene for sigma (rpoD) is located at the metC-argG region, probably near the dnaG locus (66 min on the current genetic map of E. coli).

Suppression of the DnaA phenotype by mutations in the rpoB cistron of ribonucleic acid polymerase in Salmonella typhimurium and Escherichia coli

A class of mutations that confer resistance to rifampin in Salmonella typhimurium and Escherichia coli also suppresses the thermosensitivity of chromosome initiation in dnaA mutants. Ribonucleic acid polymerase is resistant to rifampin in vitro in these suppressive mutants, and the suppressors of dnaA cannot be separated from the rpoB mutations by transduction. It is concluded, therefore, that certain rpoB mutations may suppress the DnaA phenotype.

Chemotactic mechanism of Salmonella typhimurium: preliminary mapping and characterization of mutants

Some new, generally nonchemotactic mutants of Salmonella typhimurium were isolated and they, together with previously isolated mutants and some from other investigators, were mapped. Most of the mutants were classified in nine complementation groups, which are probably individual genes. Of these, five map at the end of the flagella region and appear in the order motB-(cheWcheP)-cheX-cheQ-cheR-flaC. Two of the mutations, cheU and cheV, map in the flaQ and flaAII genes, respectively. The remaining genes, cheS and cheT, have not yet been mapped. Most of the mutants are phenotypically smoothly swimming, but some are constantly tumbling. Two of the groups show dominant behavior as recipients in genetic crosses; the rest are recessive. The mutants vary in their responses to stimuli but, since their responses to all chemoeffectors are abnormal, the central processing, rather than individual, receptors must be impaired. The two mutations that coincide with genes for flagella probably involve the locus of the final delivery of sensing signal to the flagella.

The product of a newly identified gene, gInF, is required for synthesis of glutamine synthetase in Salmonella

The product of a newly identified gene, glnF, which is distinct from the glutamine synthetase structural gene (glnA), is required for synthesis of glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2[ in Salmonella typhimurium and probably in Escherichia coli. Salmonella strains with ICR (2-chloro-6-methoxy-9-[3-(2-chloroethyl)aminopropylamino]acridine dihyodrochloride)-induced (frameshift) mutations in glnF are glutamine auxotrophs; they have less than 10% oof wild-type glutamine synthetase activity or antigen and are unable to derepress the synthesis of the enzyme. The mutant allele is recessive to the wild-type allele, indicating that the glnF gene encodes a diffusible product. Mutant glnF strains have normal activities of all proteins involved in covalent modification of glutamine synthetase: adenylyltransferase (EC 2.7.7.42), PII, uridylyltransferase, and uridylyl removing enzyme. In addition, they have glutamate synthase (EC 1.4.1.13) and glutamate dehydrogenase (EC 1.4.1.4) activities. Thus, glnF does not encode the structure of any of these proteins. The above evidence suggests that the product of the glnF gene is (or produces) a positive regulatory factor that is required for synthesis of glutamine synthetase; it indicates that auto-regulation cannot account for control of the synthesis of glutamine synthetase in Salmonella.

Chromosomal location of gene governing the trehalose utilization in Escherichia coli K12

Several mutants unable to utilize trehalose were isolated from Escherichia coli, Their genetic analysis led to determine the following gene order on the chromosomal map: pur B-dad R-tre-hem a-trp. Furthermore, the tre gene belongs to the inversion of the trp chromosomal region between E. coli and S. typhimurium.

Identification of a protein methyltransferase as the cheR gene product in the bacterial sensing system

Methylation of membrane-bound proteins with apparent molecular weights around 65,000 does not occur in mutants of the generally nonchemotactic cheR class of Salmonella typhimurium. This was shown to be due to the lack of a protein methyltransferase in these mutants by means of an in vitro assay using soluble proteins, membranes, and S-adenosylmethionine as the methyl donor. The methylase from the wild type was purified, characterized, and shown to be of molecular weight 38,000. It is specific for proteins in S. typhimurium and Escherichia coli membranes. The methylase is not required for tumbling but appears to be essential for maintaining the appropriate rate constants and levels of the regulator of the chemotactic response.

Pyrimidine biosynthesis in Serratia marcescens: a possible role for nonsequential enzyme interactions in mimicking coordinate gene expression

The coordinate expression of four sequential enzymes in the de novo pyrimidine pathway may result from the interaction of the various polypeptides of the pathway in Serratia marcescens rather than represent some unit of transcriptional regulation. These interactions were defined by examining the polypeptide association observed in extracts of parental and mutant strains in a series of pleiotropic pyrimidine auxotrophs. Extracts of pyrE auxotrophs [processing dihydroorotate (DHOase) activity but no orotidine-5'-monophosphate pyrophosphorylase (OMPppase) activity] stimulate OMPppase activity in extracts of pyrC auxotrophs (posessing reduced OMPppase activity but no DHOase activity). Separation by molecular weight on Sephadex G200 has suggested an aggregation between the final two enzymes, OMPppase and OMPdecarboxylase (OMPdecase), and the earlier enzyme, DHOase. The reduction of OMPppase activity in pyrC auxotrophs (encoding either a defective polypeptide or reduced levels) is explained by the lack of adequate levels of DHOase for aggregate formation. Such polypeptide interactions appear to mimic the coordinate formation of polypeptides which are controlled as a unit of regulation. The measurable levels of enzymatic activity vary in a quantitatively identical manner, but the variation does not result directly from the regulation of polypeptide formation.

Biosynthesis of bacterial glycogen: genetic and allosteric regulation of glycogen biosynthesis in Salmonella typhimurium LT-2

Structural gene mutants of the glycogen biosynthetic enzymes adenosine diphosphate glucose pyrophosphorylase (glgC) and glycogen synthase (glgA) were isolated and partially characterized. The cotransduction frequencies of these genes with the aspartic semialdehyde dehydrogenase (asd) and glycerol-3-phosphate dehydrogenase (glpD) genes suggested the unambiguous gene order of glpD glgA glgC asd. The results of the three-factor cross glpD- glgA- glgC+ X glpD+ glgA+ glgC- were consistent with the proposed order. A simultaneous and approximately equivalent derepression of the glgC, glgA, and glgB (branching enzyme) gene products was observed in the late logarithmic-early stationary phase of growth on enriched media. These results are consistent with the coordinately regulated synthesis of the three glycogen biosynthetic enzymes in Salmonella typhimurium.