Linkage map of Salmonella typhimurium, edition V

Characterization of a cold-sensitive hisW mutant of Salmonella typhimurium

Previous studies of hisW mutants of Salmonella typhimurium have led to the suggestion that such strains are defective in tRNA maturation. (J. E. Brenchley and J. Ingraham, J. Bacteriol. 114:528-536, 1973). In this study, we report that one hisW strain is defective in the accumulation of all stable RNA species. Polyacrylamide gel electrophoresis of radiolabeled RNA indicated tha at the nonpermissive temperature (20 degrees C) all stable RNa species in the cold-sensitive hisW3333 mutant were synthesized and rapidly degraded. We propose that the cold sensitivity of this strain is caused by such a restriction in stable RNA accumulation at low temperature. In vitro and in vivo studies demonstrated that the RNA degraded in this strain was synthesized de novo and was not preexisting RNA. Furthermore, physiological and genetic recovery from the cold-sensitive hisW phenotype resulted in relatively normal RNA synthesis and accumulation. Thus, the RNA alterations observed in this strain were not explained by defects in a tRNA modification enzyme. Rather, these findings suggest the existence of defective RNA processing and that a control mechanism for the overall synthesis or accumulation of stable RNA species is altered in the hisW3333 mutant.

Altered regulation of isoleucine-valine biosynthesis in a hisW mutant of Salmonella typhimurium

Control of isoleucine-valine biosynthesis was examined in the cold-sensitive hisW3333 mutant strain of Salmonella typhimurium. During growth at the permissive temperature (37 degrees C), the isoleucine-valine (ilv) biosynthetic enzyme levels of the hisW mutant were two- to fourfold below these levels in an isogenic hisW+ strain. Upon a reduction in growth temperature to partially permissive (30 degrees C), the synthesis of these enzymes in the hisW mutant was further reduced. However, synthesis of the ilv enzymes was responsive to the repression signal(s) caused by the addition of excess amounts of isoleucine, valine, and leucine to the hisW mutants. Such a "super-repressed" phenotype as that observed in this hisW mutant is similar to that previously shown for the hisU1820 mutant, but was different from the regulatory response of the hisT1504 mutant strain. Moreover, by the use of growth-rate-limiting amounts of the branched-chain amino acids, it was shown that this hisW mutant generally did not increase the synthesis of the ilv enzymes as did the hisW+ strain. Overall, these results are in agreement with the hypothesis that the hisW mutant is less responsive to ilv specific attenuation control than is the hisW+ strain and suggest that this limited regulatory response is due to an alteration in the amount or structure of an element essential to attenuation control of the ilv operons.

Transcriptional activity of the transposable element Tn10 in the Salmonella typhimurium ilvGEDA operon

Polarity of Tn10 insertion mutations in the Salmonella typhimurium ilvGEDA operon depends on both the location and the orientation of the Tn10 element. One orientation of Tn10 insertions in ilvG and ilvE permits low-level expression of the downstream ilvEDA and ilvDA genes, respectively. Our analysis of Salmonella ilv recombinant plasmids shows that this residual ilv expression must result from Tn10-directed transcription and does not reflect the presence of internal promoters in the ilvGEDA operon, as was previously suggested. The opposite orientation of Tn10 insertion in ilvE prevents ilvDA expression, indicating that only one end of Tn10 is normally active in transcribing adjacent genes. Both orientations of Tn10 insertion in ilvD exert absolute polarity on ilvA expression. Expression of ilvA is known to be dependent on effective translation of ilvD, perhaps reflecting the lack of a ribosome binding site proximal to the ilvA sequence. Therefore, recognition of the ability of Tn10 to promote transcription of contiguous genes in the ilvGEDA operon apparently requires the presence of associated ribosome binding sites.

Isolation and characterization of purine regulatory mutants of Salmonella typhimurium with an episomal purE-lac fusion

Expression of the purE operon of Salmonella typhimurium was analyzed by using an Escherichia coli F' episome containing a purE-lac fusion. The fusion removes the lacOP and part of the lacZ genes of the lac operon and places the intact lacY and lacA genes under control of the purE operon as shown by inhibition of growth on melibiose (lacY) and repression of thiogalactoside transacetylase (lacA) by various purines. Two classes of regulatory-deficient mutants were found among those resistant to inhibition by purines. One class was trans active (chromosomal) and corresponded to previously described purR mutants involving a deficient cytoplasmic repressor substance. These were also altered in the expression of the purF, purD, purG amd purI genes as evidenced by loss of repressibility of the synthesis of glycinamide ribotide and aminoimidazole ribotide. The other class was cis active (episomal), specific for only purE expression, and thus corresponded to an altered purE operon signal (operator or promoter). The metabolic requirements for the expression of purE were also monitored by measuring repression of the transacetylase in strains with various genetically altered metabolic backgrounds. Repression by guanine required an intact guanine phosphorbosyltransferase (gpt) and repression by adenine and all nucleosides required purine nucleoside phosphorylase (deoD). Synthesis of cyclic AMP (cya) and its receptor protein (crp) were no longer required for the expression of the lac genes under purE control.

Discontinuity of homology of Escherichia coli and Salmonella typhimurium DNA in the lac region

Partial homology of Salmonella typhimurium DNA to Escherichia coli DNA was demonstrated by Southern hybridization blots to exist on either side of the lac operon of E. coli but no homology was detected between S. typhimurium DNA and about 12 kb of E. coli DNA including the lac genes as well as about 5 kb of E. coli DNA between lac and proC. Thus portions of DNA seem to have been either added to the E.coli genome or deleted from the S. typhimurium genome since their divergence from a common ancestor. Although an IS1 element was located near the lac operon of E. coli, the insertional element was shown not to be near any of the junctures of discontinuity of E. coli--S. typhimurium homology near lac.

Isolation and mapping of a uracil-sensitive mutant of Salmonella typhimurium

A uracil-sensitive mutant of Salmonella typhimurium was isolated by diethyl sulfate mutagenesis and penicillin counterselection. This mutation identifies a new Salmonella gene that is well separated from the structural genes for arginine and pyrimidine biosynthesis. The use-1 mutation was located between the ilv gene cluster (isoleucine-valine operon) and hisR (structural gene for histidine tRNA) at 83 map units.

Genetic characterization of the glutamate dehydrogenase gene (gdhA) of Salmonella typhimurium

Salmonella typhimurium mutants, either devoid or glutamate dehydrogenase activity or having a thermolabile glutamate dehydrogenase protein, were used to identify the structural gene (gdhA) for this enzyme. Transductions showed that the mutations producing these phenotypes were linked to both the pncA and nit genes, placing the gdhA locus between 23 and 30 U on the S. typhimurium chromosome. Additional transductions with several Tn10 insertions established the gene order as pncA-gdhA-nit. Since few genetic markers exist in this region of the chromosome, Hfr strains were constructed to orient the pncA-gdhA-nit cluster with outside genes. Conjugation experiments provided evidence for the gene order pyrD-pncA-gdhA-nit-trp. To further characterize gdhA, we used Mu cts d1 (Apr lac) insertions in this gene to select numerous strains containing deletions with various endpoints. Transductions of these deletions with strains containing different gdh mutations and with a mutant having a thermolabile glutamate dehydrogenase protein permitted us to construct a deletion map of the gdhA region.

Recombination between two IS/s flanking the r-determinant of R100-1: involvement of dor and recA gene functions in Salmonella typhimurium

Drug resistance genes of the r-determinant component of a composite R plasmid R100-1 were frequently lost in Salmonella typhimurium. Various deletion mutants were analyzed by restriction endonuclease cleavage, Southern blotting, and hybridization techniques. The loss of the r-determinant was found to be the result of a reciprocal recombination between the two IS/s flanking the r-determinant. This recombination depended upon both dor and recA gene functions.

Identification of the structural genes for glutamate synthase and genetic characterization of this region of the Salmonella typhimurium chromosome

Salmonella typhimurium cells require glutamate synthase activity for growth in media containing a growth rate-limiting nitrogen source. Although this enzyme plays a critical role in ammonia assimilation, little is known about the organization and regulation of the structural genes for its two subunits. To identify the location of the structural genes, mutants having heat-labile glutamate synthase activities were isolated and characterized. Mutations that altered glutamate synthase activity were mapped at 69 U on the S. typhimurium chromosome. Four strains with independent Tn10 insertions in this region were constructed and used for mutant selection and for positioning mutations affecting glutamate synthase activity relative to other genetic markers. In contrast to results obtained with Escherichia coli mutants, there was no linkage between mutations affecting glutamate synthase activity and the argG gene. The results of a combination of transduction experiments demonstrated the gene order argG-glnF-gltB-cod-argR-envB-aroE for S-typhimurium.

Regulation of L-arabinose transport in Salmonella typhimurium LT2

The inducible L-arabinose transport system was characterized in Salmonella typhimurium LT2. Only one L-arabinose transport system with a Km of 2 X 10(-4) M was identified. The results suggested that araE may be the only gene which codes for L-arabinose transport activity under the conditions tested. An araE-lac fusion strain was used to study the induction of the araE gene. No araE expression was detected when the L-arabinose concentration was lower than 1 mM. The expression of araE reached a maximum in the presence of 50 mM L-arabinose, and was significantly reduced in the presence of 50 mM L-arabinose, and was significantly reduced in the presence of D-glucose. Expression of the araBAD and araE genes was coordinately regulated. The concentration of L-arabinose that allowed maximum araBAD gene expression was 50-fold lower in an araE+ strain compared to an araE strain.

Repression of cytosine deaminase by pyrimidines in Salmonella typhimurium

The synthesis of cytosine deaminase in Salmonella typhimurium is repressed by pyrimidines. This repression is mediated by both a uridine and a cytidine compound, indicating a distinct difference in the regulation of synthesis of cytosine deaminase from the regulation of the de novo pyrimidine pathway enzymes. A salvage role for the enzyme in pyrimidine metabolism is postulated.

Genetic and biochemical analyses of pantothenate biosynthesis in Escherichia coli and Salmonella typhimurium

Pantothenate (pan) auxotrophs of Escherichia coli K-12 and Salmonella typhimurium LT2 were characterized by enzymatic and genetic analyses. The panB mutants of both organisms and the pan-6 ("panA") mutant of S. typhimurium are deficient in ketopantoate hydroxymethyltransferase, whereas the panC mutants lack pantothenate synthetase. panD mutants of E. coli K-12 were previously shown to be deficient in aspartate 1-decarboxylase. All mutants showed only a single enzyme defect. The finding that the pan-6 mutant was deficient in ketopantoate hydroxymethyltransferase indicates that the genetic lesion is a panB allele. The pan-6 mutant therefore is deficient in the utilization of alpha-ketoisovalerate rather than the synthesis of alpha-ketoisovalerate, as originally proposed. The order of the pan genes of E. coli K-12 was determined by phage P1-mediated three-factor crosses. The clockwise order was found to be aceF panB panD panC tonA on the genetic map of E. coli K-12. The three-factor crosses were greatly facilitated by use of a closely linked Tn10 transposon as the outside marker. We also found that supplementation of E. coli K-12 auxotrophs with a high concentration of pantothenate or beta-alanine increased the intracellular coenzyme A level two- to threefold above the normal level. Supplementation with pantoate or ketopantoate resulted in smaller increases.

Salmonella typhimurium mutants defective in the formate dehydrogenase linked to nitrate reductase

Six fdn mutants of Salmonella typhimurium defective in the formation of nitrate reductase-linked formate dehydrogenase (FDHN) but capable of producing both the hydrogenase-linked formate dehydrogenase (FDHH) and nitrate reductase were characterized. Results of phage P22 transduction experiments indicated that there may be three fdn genes located on the metE-metB chromosomal segment and distinct from all previously identified fdh and chl loci. All six FDHH+ FDHN- mutants were found to make FDHN enzyme protein which was indistinguishable from that of the wild type in electrophoretic studies. However, the results of the spectral studies indicated that all six mutants were defective in the anaerobic cytochrome b559 associated with FDHN. All contained the cytochrome b559 associated with nitrate reductase in amounts equal to or greater than the wild type. The results of the transduction experiments also indicated that the metE- metB segment of the Salmonella chromosome resembles that of Escherichia coli more than was originally thought.

Methionine sulfoxide is transported by high-affinity methionine and glutamine transport systems in Salmonella typhimurium

Three lines of evidence indicated that methionine sulfoxide is transported by the high-affinity methionine and glutamine transport systems in Salmonella typhimurium. First, methionine-requiring strains (metE) which have mutations affecting both of these transport systems (metP glnP) were unable to use methionine sulfoxide as a source of methionine. These strains could still grow on L-methionine because they possessed a low-affinity system (or systems) which transported L-methionine but not the sulfoxide. A methionine auxotroph with a defect only in the metP system, which was dependent upon the glnP+ system for the transport of methionine sulfoxide, was inhibited by L-glutamine because glutamine inhibited the transport of the sulfoxide by the glnP+ system. Second, a metE metP glnP strain could be transduced at either the metP or glnP genes to restore its ability to grow on methionine sulfoxide. Third, the transport of [14C]methionine sulfoxide was inhibited by methionine and by glutamine in the metP+ glnP+ strain. No transport was detected in the metP glnP double-mutant strain.

Vaccinal properties of Salmonella abortus ovis mutants for streptomycin: screening with a murine model

Streptomycin-dependent and streptomycin-independent reverse mutants of Salmonella abortus ovis were selected on medium with and without added streptomycin. Their in vivo properties were tested with a murine model. Reduced capacities of dissemination and multiplication of all mutant strains were evidenced by means of subcutaneous, intraperitoneal, and intravenous inoculations of two outbred strains of mice with different susceptibilities to experimental S. abortus ovis infection. A factorial immunization experiment demonstrated the effects of vaccinal strains and doses. It showed large differences among the mutants. First-time infection with the fully virulent parent strain excepted, the best protection was given by independent reverse mutants which had kept residual capacity of in vivo dissemination and multiplication. This screening partly determined the selection of strain Rv6 as a potential live vaccine.

Influence of lipopolysaccharide and protein in the cell envelope on recipient capacity in conjugation of Salmonella typhimurium

In crosses of Salmonella typhimurium FfinP301 lac+ to F- strains of S. typhimurium in broth, recipient strains which were rough mutants affected in the outer core region of the lipopolysaccharide gave an average of 1.4 Lac+ transconjugants per donor cell and over 50% of the donor and recipient cells in mating aggregates, whereas smooth recipient strains gave 0.08 Lac+ transconjugants and few cells in mating aggregates. Strains with mutations affecting the inner core of the lipopolysaccharide were usually poor recipients. When cells were mated on Millipore membrane filters, both smooth and rough strains gave ca. 1.0 Lac+ transconjugants per donor cell. Plasmids in Inc groups FI, FII, M, J, and I beta gave more transconjugants with rough than smooth strains, but there were no difference in crosses with plasmids in Inc groups T, L, P, N, and W. Strains with mutations in the ompA gene (deficient in Omp Ap = 33K = II* = conjugation protein) yielded only 0.02 Lac+ transconjugants per donor cell and few cells in mating aggregates. There was no indication of a deficiency of Omp Ap in smooth strains compared with rough strains. Reduced fertility of smooth recipients may occur because the O side chains of the lipopolysaccharide shield the recipient and reduce the frequency of stabilization of mating aggregates. However, gradient-of-transmission experiments indicated that once these mating aggregates are stabilized, they are equally stable in both smooth and rough recipients. Fertility was high in crosses of S. typhimurium Flac+ to Escherichia coli K-12 F- (0.75 Lac+ transconjugants per donor cell; over 50% of the cells in mating aggregates). In crosses of E. coli K-12 Flac+ to S. typhimurium smooth F-, ca. 10(-5) Lac+ transconjugants per donor cell were obtained; in crosses to rough recipient strains, fertility was increased 14-fold, and when the recipient was defective in the SA and LT host restriction systems, fertility was increased in additional 100-fold. Thus, both the lipopolysaccharide and the protein in the cell envelope of S. typhimurium were shown to be important in the recipient function in F-mediated conjugation.

Genetic mapping of the Salmonella typhimurium pncB locus

The nicotinic acid phosphoribosyltransferase locus pncB was located on the Salmonella typhimurium linkage map counterclockwise relative to pyrC. P22 and P1 transductional analyses revealed linkage of pncB with aroA and pyrD, indicating a pncB map position of approximately 20 map units. The results of these cotransduction experiments also indicated that the genetic map distance between gal and pyrD is greater than the published 2.2 map units.

Genetics of the glutamine transport system in Escherichia coli

The active transport of glutamine by Escherichia coli occurs via a single osmotic shock-sensitive transport system which is known to be dependent upon a periplasmic binding protein specific for glutamine. We obtained a mutant that had elevated levels of glutamine transport and overproduced the glutamine binding protein. From this strain many point mutants and deletion-carrying strains defective in glutamine transport were isolated by a variety of techniques. The genetic locus coding for the glutamine transport system, glnP, and the regulatory mutation which causes overproduction of the transport system were both shown to map at 17.7 min on the E. coli chromosome, and it was demonstrated that the glnP locus contains the structural gene for the glutamine binding protein. Evidence was also obtained that the glutamine transport system, by an unknown mechanism, plays a direct role in the catabolism of glutamate and, hence, of glutamine and proline as well.

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.

Spontaneous mutators of salmonella typhimurium LT2 generated by insertion of transposable elements

Spontaneous mutators of Salmonella typhimurium LT2 were generated by inserting the transposable element Tn5 or Tn10 into the bacterial chromosome. Two mutators mapped at the position of the mutH and mutL loci of S. typhimurium, and two other mutators mapped at positions corresponding to the mutS and uvrD loci of Escherichia coli. A fifth mutator, mutB, did not map at a position corresponding to any of the known mutators of S. typhimurium or E. coli. The mutH,L,S and uvrD alleles increased the frequency of both spontaneous base substitution and frameshift mutations, whereas the mutB allele increased the frequency only of spontaneous base substitution mutations. The increased frequency of base substitution mutations was recA+ independent in the mutH, mutL, and uvrD strains and partially recA+ independent in the mutS strain. The uvrD mutation decreased the resistance of the cells to killing by ultraviolet irradiation. The mutH,L,S and uvrD strains showed an increased sensitivity to mutagenesis by the alkylating agents methyl methane sulfonate and ethyl methane sulfonate, but not to mutagenesis by 4-nitroquinoline-1-oxide.

Molecular cloning and expression of the ilvGEDAY genes from Salmonella typhimurium

The ilvGEDAY genes of Salmonella typhimurium were cloned in Escherichia coli K-12 by in vitro recombination techniques. A single species of recombinant plasmid, designated pDU1, was obtained by selecting for Valr Ampr transformants of strain SK1592. pDU1 was shown to contain a 14-kilobase EcoRI partial digestion product of the S. typhimurium chromosome inserted into the EcoRI site of the pVH2124 cloning vector. The ilvGEDAY genes were found to occupy a maximum length of 7.5 kilobases. Restriction endonuclease analysis of the S. typhimurium ilv gene cluster provided another demonstration of the gene order as well as established the location of ilv Y between ilvA and ilvC. The presence of a ribosomal ribonucleic acid operon on the pDU1 insert, about 3 kilobases from the 5' end of ilvG, was shown by Southern hybridization. The expression of the ilvGEDA operon from pDU1 was found to be elevated, reflecting the increased gene dosage of the multicopy plasmid. A polarity was observed with respect to ilvEDA expression which is discussed in terms of the possible translational effects of the two internal promoter sequences, one located proximal to ilvE and the other located proximal to ilvD.

Molecular cloning of chemotaxis genes and overproduction of gene products in the bacterial sensing system

The chemotaxis genes cheR, cheB, cheY, cheZ, and tar of Salmonella typhimurium were cloned into bacteriophage lambda vectors and onto pBR322 plasmids by recombinant DNA techniques. The genes were linearly arranged in the order tar-cheR-cheB-cheY-cheZ (and were read from a promoter on the upstream side of the tar or cheR gene). However, their stoichiometries of expression were found to be 4:1:1:18:3, respectively. The overexpression of the cheY gene appeared to be a function of translational control. These five che genes were placed on a multicopy plasmid, and the gene products were overproduced in the cells, as shown by enzyme assays. The overproduction of the products of these five genes relative to those of the other che genes caused some changes in chemotactic properties, but no dramatic destruction of sensing ability.

Physical map of the Salmonella typhimurium histidine transport operon: correlation with the genetic map

A detailed restriction map of a 12.4-kilobase EcoRI fragment of Salmonella typhimurium deoxyribonucleic acid (DNA) containing the entire histidine transport operon and the argT gene is presented. Subclones of specific regions of the transport operon of S. typhimurium were constructed in plasmid vectors. An accurate correlation between the restriction map and the location of genetically defined deletions was obtained by hybridizing restriction digests of chromosomal DNA from strains carrying each deletion with cloned transport operon DNA as a probe. These data were used to position the histidine transport genes on the cloned 12.4-kilobase fragment of DNA.

Defective enzyme II-BGlc of the phosphoenolpyruvate:sugar phosphotransferase system leading to uncoupling of transport and phosphorylation in Salmonella typhimurium

Transport and phosphorylation of glucose via enzymes II-A/II-B and II-BGlc of the phosphoenolpyruvate:sugar phosphotransferase system are tightly coupled in Salmonella typhimurium. Mutant strains (pts) that lack the phosphorylating proteins of this system, enzyme I and HPr, are unable to transport or to grow on glucose. From ptsHI deletion strains of S. typhimurium, mutants were isolated that regained growth on and transport of glucose. Several lines of evidence suggest that these Glc+ mutants have an altered enzyme II-BGlc as follows. (i) Insertion of a ptsG::Tn10 mutation (resulting in a defective II-BGlc) abolished growth on and transport of glucose in these Glc+ strains. Introduction of a ptsM mutation, on the other hand, which abolishes II-A/II-B activity, had no effect. (ii) Methyl alpha-glucoside transport and phosphorylation (specific for II-BGlc) was lowered or absent in ptsH+,I+ transductants of these Glc+ strains. Transport and phosphorylation of other phosphoenolpyurate:sugar phosphotransferase system sugars were normal. (iii) Membranes isolated from these Glc+ mutants were unable to catalyze transphosphorylation of methyl alpha-glucoside by glucose 6-phosphate, but transphosphorylation of mannose by glucose 6-phosphate was normal. (iv) The mutation was in the ptsG gene or closely linked to it. We conclude that the altered enzyme II-BGlc has acquired the capacity to transport glucose in the absence of phosphoenolpyruvate:sugar phosphotransferase system-mediated phosphorylation. However, the affinity for glucose decreased at least 1,000-fold as compared to the wild-type strain. At the same time the mutated enzyme II-BGlc lost the ability to catalyze the phosphorylation of its substrates via IIIGlc.

Genetic analysis of a temperature-sensitive Salmonella typhimurium rho mutant with an altered rho-associated polycytidylate-dependent adenosine triphosphatase activity

A conditional-lethal rho mutant of Salmonella typhimurium LT2 has been isolated. The mutation was selected as a suppressor of the polarity of an insertion sequence (IS)2-induced mutation (gal3) carried on an F' plasmid. In addition to suppression of IS2-induced polarity, the rho-111 mutation suppressed nonsense and frameshift polarity. The rho-associated polycytidylic acid-dependent adenosine triphosphatase activity in the mutant strain was elevated 15-fold above that in the parental strain, and the mutant rho protein was thermally unstable. A temperature-resistant revertant of the mutant strain did not suppress polarity and contained normal levels of polycytidylic acid-dependent adenosine triphosphatase, suggesting that the phenotype of the rho-111-bearing strain is the consequence of a single mutation. The rho-111 mutation was located on the S. typhimurium linkage map midway between the ilv and cya loci by phage P22 cotransduction studies. F' plasmid maintenance was not impaired in the mutant strain, and the mutation was recessive to the wild-type allele. The rho-111 mutation did not alter in vivo expression of either the tryptophan or histidine operons.

Genetic mapping of a mutation conferring sensitivity to bacteriophage Mu in Salmonella typhimurium LT2

Two strains of Salmonella typhimurium LT2, SA1475 and MA411, were fortuitously found to be sensitive to bacteriophage Mu. The Mu-sensitivity allele of SA1475 was called musA1 and shown to be linked to the histidine operon both in conjugation and transduction experiments. The Mus allele of MA411 was unlinked to the his region and was tentatively designated musB2. Strains carrying large deletions of the his operon were also tested for Mu sensitivity; those of which the his-rib region is deleted were also sensitive to Mu. Transduction data led to the order zee-2 hisOGDCBAHFIE gnd musA. An Hfr injecting the his operon early (HfrK9) an carrying hisG9424::Tn10 delta 4 delta 11 and musA1 was isolated; this Hfr made it possible to introduce the Mus character into most derivatives of S. typhimurium LT2. Since strain SA1475 is resistant to bacteriophage P1, it could be used to select a new P1-Mu hybrid which has the host range of Mu and the transduction properties of P1.

Regulation of methyl beta-galactoside permease activity in pts and crr mutants of Salmonella typhimurium

We have studied the regulation of the synthesis and activity of a major galactose transport system, that of methyl beta-galactoside (MglP), in mutants of Salmonella typhimurium. Two classes of mutation that result in a (partially) defective phosphoenolpyruvate: sugar phosphotransferase system (PTS) interfere with MglP synthesis. pts mutations, which eliminate the general proteins of the PTS Enzyme I and/or HPr and crr mutations, which result in a defective glucose-specific factor IIIGlc of the PTS, lead to a low MglP activity, as measured by methyl beta-galactoside transport. In both ptsH,I, and crr mutants the amount of galactose binding protein, one of the components of MglP, is only 5%-20% of that in wild-type cells, as measured with a specific antibody. We conclude that synthesis of MGlP is inhibited in pts and crr mutants. Once the transport system is synthesized, its transport activity is not sensitive to PTS sugars (i.e., no inducer exclusion occurs). The defect in pts and crr mutants with respect to MGlP synthesis can be relieved in two ways: by externally added cyclic adenosine 3',5-monophosphate (cAMP) or by a mutation in the cAMP binding protein. The conclusion that MglP synthesis is dependent on cAMP is supported by the finding that its synthesis is also defective in mutants that lack adenylate cyclase. pts and crr mutations do not affect growth of S. typhimurium on galactose, however, since the synthesis and activity of the other major galactose transport system, the galactose permease (GalP), is not sensitive to these mutations. If the galactose permease is eliminated by mutation, growth of pts and crr mutants on low concentrations of galactose becomes very slow due to inhibited MglP synthesis. Residual growth observed at high galactose concentrations is the result of yet another transport system with low affinity for galactose.

Gene rfaH, which affects lipopolysaccharide core structure in Salmonella typhimurium, is required also for expression of F-factor functions

Mutations in gene rfaH of Salmonella typhimurium at 84 units on the linkage map make lipopolysaccharide of chemotypes Ra, Rb2, Rb3, and Rc (A. A. Lindberg and C. G. Hellerqvist, J. Gen. Microbiol, 116:25--32, 1980). F-factor expression in RfaH- strains was reduced in the following properties when compared with RfaH+ strains: transfer of Flac, number of phage f2 infective centers, lysis by and propagation of phages f2 and M13, proportion of cells with visible F-pili, and formation of mating aggregates with F- cells. Inhibition of multiplication of Br60, a female-specific phage, was not reduced in RfaH- Flac strains. Plasmid transfer from RfaH- strains was reduced for Inc groups FI, FII, and T, unaffected for Inc groups beta, I alpha, L, N, P, and W. and increased for Inc group M when compared with plasmid transfer from RfaH+ strains. Reduced F-factor function in RfaH- strains was not due to defective lipopolysaccharide since strains with mutations in other rfa genes were unaffected in plasmid transfer. Gene rfaH appears to be homologous with gene sfrB in Escherichia coli K-12, which maps at the same location, influences F-factor function, and affects synthesis of lipopolysaccharide. The gene product of sfrB has been proposed to be a transcription antiterminator.

Spontaneous tandem genetic duplications in Salmonella typhimurium arise by unequal recombination between rRNA (rrn) cistrons

A method is described to detect and measure the frequency of spontaneous tandem genetic duplications located throughout the Salmonella genome. The method is based on the ability of duplication-containing strains to inherit two selectable alleles of a single gene during generalized transductional crosses. One allele of the gene carries an insertion of the translocatable tetracycline-resistance element Tn10; the other allele is a wild-type copy of that gene. Using this technique, we have measured the frequency of tandem duplications at 38 chromosomal sites and the amount of material included in 199 independent duplications. These results suggest that, in one region of the chromosome, tandem duplications are particularly frequent events. Such duplications have end points within rRNA (rrn) cistrons and probably arise by unequal cross-over between these dispersed repeated sequences. Spontaneously duplications of this type are harbored by as much as 3% of the bacterial population. Preliminary evidence suggests that such duplications may play a significant regulatory role under conditions of rapid growth. Our analysis has suggested the position on the genome of an additional rRNA cistron.

Identification and localization of a gene that specifies production of Escherichia coli DNA topoisomerase I

A gene that specifies production of Escherichia coli DNA topoisomerase I (omega protein) was identified with the aid of a radioimmunoassay for this protein. E. coli DNA topoisomerase I was produced by Salmonella typhimurium merodiploids that harbored E. coli plasmid F' 123, but not by strains that lost this plasmid. Analysis of strains with spontaneous deletions of F' 123 showed that the gene, topA, required for production of the E. coli omega protein was between the trp operon and the cysB gene. Deletions that eliminated topA also eliminated the supX gene. We suggest that topA is the structural gene of E. coli DNA topoisomerase I and that topA is identical to supX.

Role of the supX gene in ultraviolet light-induced mutagenesis in Salmonella typhimurium

Salmonella typhimurium strains with supX mutations are more sensitive than wild type to killing by ultraviolet (UV) irradiation. Studies with strains bearing the leuD21 mutation revealed that inactivation of the supX locus by a nonsense mutation or a deletion results in a complete lack of ability to produce induced Leu+ reversion mutations after UV irradiation. Suppression of the nonsense supX mutation or the presence of an Escherichia coli K-12 F'-borne supX+ allele restored the capacity for induced reversions and increased cell survival after UV irradiation. Introduction of plasmid pKM101 into supX mutant strains also restored their capacity for UV mutagenesis as well as increased survival. The possible nature of the supX gene product and mechanisms by which it may affect expression of the inducible SOS error-prone repair system are considered.

Genetic characterization of the araE gene in Salmonella typhimurium lt2

Six L-arabinose transport-deficient mutants of Salmonella typhimurium LT2 were isolated on the basis of their inability to ferment low concentrations of L-arabinose. The mutations were localized between serA and lys on the S. typhimurium genetic map and assigned to the araE locus. An araE-lac fusion strain was constructed and used to determine that the direction of araE transcription was counterclockwise on the S. typhimurium genetic map. beta-Galactosidase activity was induced by L-arabinose in the araE-lac fusion strain, suggesting that araE expression is controlled at the level of transcription.

Flurorcitrate resistant tricarboxylate transport mutants of Salmonella typhimurium

Spontaneous and Tn10 induced fluorocitrate resistant mutants were isolated and characterized. These mutants were unable to grow on either cis-aconitate or DL-isocitrate but were still able to grow slowly on sodium citrate and normally on potassium or potassium-plus-sodium citrate. These mutants were defective in both citrate transport and citrate binding to priplasmic proteins. Tn10 insertion mutants were unable to produce immunologically detectable amounts of the citrate inducible periplasmic C protein previously shown to bind tricarboxylates. Using a series of tct::Tn10 directed Hfrs the tct locus was accurately positioned at 59 units between srlA and pheA, but was not cotransducible with either gene. In the absence of P22 mediated cotransduction with 16 adjacent chromosomal markers the srlA and tct loci were bridged by using a series of tct flanking Tn10 insertions, and by newly isolated and characterized nalB mutants. In addition the hyd and recA loci were located establishing the gene order in this region of the chromosome as: pheA tct nalB recA srlA hyd cys. Nitrosoguanidine derived tricarboxylate mutations (Imai 1975) were also mapped within the tct locus.

Organization and regulation of the ilvGEDA operon in Salmonella typhimurium LT2

A total of 102 isoleucine- and isoleucine-valine-requiring (ilv) mutants induced by insertion of the transposable element Tn10 have been classified to cistron by growth requirement, cross-feeding behavior, and enzyme assays. The mutations are in a polycistronic operon transcribed in the order ilvGEDA and in a monocistronic operon ilvC. Analysis of distal gene expression in these polar insertion mutants revealed the existence of two constitutive interval promoters, one preceding ilvE and the other preceding ilvD.

A Salmonella typhimurium mutant dependent upon carbamyl aspartate for resistance to 5-fluorouracil is specifically affected in ubiquinone biosynthesis

The isolation and properties of a mutant dependent upon exogenous carbamyl aspartate for resistance to 5-fluorouracil are described. The mutant was deficient in the synthesis of ubiquinone and accumulated a quinone provisionally identified as the ubiquinone precursor 2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone. The mutation resulted in an alteration in the regulation of synthesis of enzymes involved in de novo pyrimidine biosynthesis but did not establish a functional block in dihydroorotate dehydrogenase activity in vivo. Conditional resistance to 5-fluorouracil apparently occurred through an inhibition of the conversion of the analog to the nucleotide level.

General Transduction in Vibrio cholerae

Evidence was obtained for general transduction in Vibrio cholerae. Transduction of three amino acid markers and three antibiotic resistance characters was demonstrated using strains of biotype eltor and biotype cholerae. Some of the genetic characters were transduced from a biotype eltor donor (and its mutant derivatives) to biotype cholerae and eltor recipients. For the genetic traits examined, the frequencies of transduction ranged between 10(-5) and 10(-8). Maximal frequencies were obtained with transducing phage lysates that were irradiated with ultraviolet light. The development of a system of general transduction will now aid in fine structure analysis and detailed mapping of the chromosome of V. cholerae.

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.

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.

Characterization of type 1 pili of Salmonella typhimurium LT2

Type 1 pili from Salmonella typhimurium LT2 were purified and characterized. The pilus filaments were 6 nm in diameter and over 1 microns long. Estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the molecular weight of the pilin was 21,000. The isoelectric point of the filament was 4.1. Hydrophobic amino acids comprised 40.3% of the total amino acids of the pilin, which contained more proline, serine, and lysine than reported for the type 1 pilin of Escherichia coli. Purified pili agglutinated both horse and chicken erythrocytes and yeast cells but not bovine, sheep, or human erythrocytes. Horse erythrocyte agglutination was inhibited at lower concentrations by alpha-methyl-D-mannoside than by yeast mannane and D-fructose. Agglutination was not affected by D-galactose or sucrose. Results of the present study confirm the role of type 1 pili as Salmonella hemagglutinins and show chemical differences between the type 1 pili of S. typhimurium and E. coli.

Salmonella typhimurium mutants with reduced levels of transfer ribonucleic acid-inhibitable endodeoxyribonucleolytic activity

Two methods of mutagenesis, chemical alkylation and insertion of the tetracycline resistance transposon Tn10, were used to generate mutants of Salmonella typhimurium which had reduced levels of endodeoxyribonucleolytic activity. The chemically induced mutations defined a locus, endA, which was cotransduced with serA at a low frequency and with metK at a high frequency. Three-factor crosses revealed that metK was between serA and endA. The major endodeoxyribonucleolytic activity in crude extracts of s. typhimurium was similar to the activity of Escherichia coli endonuclease I. A Tn10 insertion mutation of endA resulted in the most severe loss of endodeoxyribonucleolytic activity among the endA alleles studied. Two of the chemically induced mutations resulted in activities which were more thermolabile than the wild-type activity.

UGA suppressor that maps within a cluster of ribosomal protein genes

A suppressor of UGA mutations (supU) maps near or within a cluster of ribosomal protein genes at 72 min on the Salmonella typhimurium genetic map. The suppressor is relatively inefficient, and its activity is abolished by rpsL (formerly strA) mutations. The suppressor is dominant to a wild-type supU allele. The map position of this suppressor suggests that it may owe its activity to an alteration of ribosome structure.

A mutation in Salmonella typhimurium imparting conditional resistance to 5-fluorouracil and a bioenergetic defect: mapping of cad

The position of the genetic locus allelic with the cad-2 mutation has been located between units 14 and 15 of the linkage map of S. typhimurium. Fine structure mapping established the gene order as cad flrB nag. The genetic evidence coupled with biochemical evidence indicates that this cad locus is homologous to the ubiF gene of Escherichia coli.

Generalized transduction in the enterobacterial phytopathogen Erwinia chrysanthemi

Bacteriophages induced by mitomycin treatment of Erwinia chrysanthemi KS612 produced plaques on lawns of E. chrysanthemi EC183 and KS605. Bacteriophage Erch-12, purified from one such plaque, transferred an array of chromosomal genes (arg, leu, his, ser, thr, trp, ura) to appropriate recipient strains derived from E. chrysanthemi EC 183. Recombinants were formed in the absence of cellular contact between donor and recipient bacteria and in the presence of deoxyribonuclease. Ultraviolet irradiation of the bacteriophage stimulated transductional frequency. Linkage was detected in two-factor crosses between the loci thr and ser and between rif and ade; several closely linked mutations in ser were mapped with respect to thr.

Isolation of ara-lac gene fusions in Salmonella typhimurium LT2 by using transducing bacteriophage Mu d (Apr lac)

A specialized Mu transducing phage containing a gene encoding ampicillin resistance and the lac structural genes without the lac promotor [Mu d(apr lac)] has been constructed and used to create gene fusions in Escherichia coli (M. J. Cadadaban and S. N. Cohen, Proc. Natl. Acad. Sci. U.S.A. 76:4530--4533, 1979). Transposition of the Mu d(Apr lac) phage to chromosomal sites can result in lac expression being controlled by a chromosomal promoter. We have constructed an Escherichia coli K-12 strain in which the Mu d(Apr lac) phage is integrated into an F factor. The F+::Mu d(Apr lac) was then transferred by conjugation into a Salmonella typhimurium strain that was sensitive to L-arabinose. Strains containing gene fusions were selected as L-arabinose-resistant colonies after partial induction of the phage. Two classes of ara-lac fusion strains were isolated: (i) araC-lac fusions in which the expression of beta-galactosidase synthesis was constitutuve and not inducible by L-arabinose; and ((ii) fusion of the lac genes to the ara structural genes in which the expression of beta-galatosidase synthesis was induced 263-fold by L-arabinose.

Genetic mapping of the Salmonella typhimurium pepB locus

Transposon technology has been used to map the pepB locus of Salmonella typhimurium. This locus is cotransducible by phage P22 with glyA and strB at min 56 on the Salmonella genetic map. The gene order is strB pepB glyA.

Polyprenyl p-hydroxybenzoate carboxylase in flagellation of Salmonella typhimurium

Flagellation of Salmonella typhimurium was found to require a functional pathway for ubiquinone biosynthesis as well as growth in the presence of appropriate carboxylic acids. Induction of flagellation by carboxylic acids was shown to induce incorporation of p-hydroxybenzoic acid into polyprenylphenol. Constitutive flagellation was found to correlate with constitutive incorporation of p-hydroxybenzoic acid into polyprenylphenol. A novel pathway for polyprenyl p-hydroxybenzoic acid decarboxylation to polyprenylphenol was implicated in flagellation of S. typhimurium.

Locations of the opp and supX genes of Salmonella typhimurium and Escherichia coli

The chromosomal locations of the supX and opp loci of Salmonella typhimurium LT2 and Escherichia coli K-12 were identified and found to result in the same gene sequence in both species, namely, pyrF-cysB-supX-trpPOLEDCBA-tonB(chr)-opp. These results differ from a previously reported location of the opp gene on the E. coli chromosome. Evidence indicates that the opp gene lies between chr(tonB) and galU in S. typhimurium.