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PubMed1970

UGA nonsense mutations in Salmonella typhimurium.

Salmonella typhimurium strain LT-2 carries a weak UGA suppressor activity. This activity prevents the detection of some UGA mutants as auxotrophs and probably accounts for the rarity of his UGA mutants in this strain. A selection method is described which permits the isolation of these rare his UGA mutants. Map distribution of his UGA mutations is normal, and their polarity effects are indistinguishable from the polarity effects of amber and ochre mutations at similar locations. Isolation and properties of a prototrophic his UGA mutant are described. UGA mutants are common among lac mutants isolated from Salmonella strains carrying an F'lac episome. Apparently the suppressor activity is insufficient to prevent detection of lac UGA mutants. It is not yet clear whether the suppressor activity plays an important role in normal cell physiology.

Chromosome Mapping↗
PubMedDate not supplied

A new plasmidic cefotaximase from patients infected with Salmonella typhimurium.

Salmonella typhimurium strains resistant to most beta-lactams, co-trimoxazole, tobramycin and gentamicin were isolated from patients in two hospitals in Buenos Aires, Argentina, beginning in August 1990. The patients were suffering from meningitis, septicaemia or enteritis. Therapy including ampicillin, ceftriaxone and gentamicin failed. The strains produced a plasmidic (pMVP-4) extended broad-spectrum beta-lactamase which is more active against cefotaxime than against ceftazidime (Vmax for cefotaxime 350 times higher than for ceftazidime). This cefotaximase demonstrates similarity to the previously described CTX-ase-M-1 from Escherichia coli, but it is distinctly different from CTX-ase-M-1 by its isoelectric point (7.9 for CTX-ase-M-2 in comparison with 8.9 for CTX-ase-M-1) as well as in its lower susceptibility to the beta-lactamase inhibitors sulbactam, clavulanic acid, tazobactam and BRL 42715. Thus, the beta-lactamase produced by S. typhimurium strains from Argentina appears to represent a new member (CTX-ase-M-2) of a novel group of plasmidic extended broad-spectrum beta-lactamases designated as cefotaximases.

Argentina↗
PubMed1993

Characterization of the cobalamin (vitamin B12) biosynthetic genes of Salmonella typhimurium.

Salmonella typhimurium synthesizes cobalamin (vitamin B12) de novo under anaerobic conditions. Of the 30 cobalamin synthetic genes, 25 are clustered in one operon, cob, and are arranged in three groups, each group encoding enzymes for a biochemically distinct portion of the biosynthetic pathway. We have determined the DNA sequence for the promoter region and the proximal 17.1 kb of the cob operon. This sequence includes 20 translationally coupled genes that encode the enzymes involved in parts I and III of the cobalamin biosynthetic pathway. A comparison of these genes with the cobalamin synthetic genes from Pseudomonas denitrificans allows assignment of likely functions to 12 of the 20 sequenced Salmonella genes. Three additional Salmonella genes encode proteins likely to be involved in the transport of cobalt, a component of vitamin B12. However, not all Salmonella and Pseudomonas cobalamin synthetic genes have apparent homologs in the other species. These differences suggest that the cobalamin biosynthetic pathways differ between the two organisms. The evolution of these genes and their chromosomal positions is discussed.

Amino Acid Sequence↗
PubMed1988

Aerobic excretion of 1,2-propanediol by Salmonella typhimurium.

Salmonella typhimurium excreted the rhamnose fermentation product 1,2-propanediol not only under anaerobic conditions, but also under aerobic conditions. The absence of an aldehyde dehydrogenase enzymatic activity that oxidizes to lactate the lactaldehyde formed in the dissimilation of rhamnose raised the intracellular concentration of the aldehyde which was alternatively reduced to the excretable 1,2-propanediol by a residual propanediol oxidoreductase activity.

Aerobiosis↗
PubMed1975

The metabolism of N4-hydroxycytidine-a mutagen for Salmonella typhimurium.

Salmonella typhimurium cells were grown in the presence of (14C)-N4-hydroxycytidine (N4OHcyd), a mutagenic nucleoside, and labelling in DNA and RNA digest was traced. The results show that this analogue is incorporated into RNA at a level of 40 mug/100 mg, and into DNA with a yield at least 100 times smaller. Some N-minus4OHcyd was rapidly metabolized and labelling was found in all ribo- and deoxyribo-nucleosides.

Centrifugation, Density Gradient↗
PubMed1979

In vivo conversion of sodium azide to a stable mutagenic metabolite in Salmonella typhimurium.

Salmonella typhimurium TA1530 and G46 strains growing in minimal medium supplemented with sodium azide produce a stable mutagenic metabolite which is not azide. The production of this metabolite is restricted to the log phase of bacteria grown in the presence of azide. The metabolite is highly mutagenic in DNA-repair defective base-substitution strains TA1530 and TA1535, but ineffective in frameshift strains TA1538 and TA1537. The metabolite induces mutations in resting cells of the TA1530 strain.

Azides↗
PubMed1982

[Phenotypes and epidemiological markers of Salmonella typhimurium].

Salmonella typhimurium is the most often encountered serotype. The need for numerous epidemiological markers seems particularly obvious. The purpose of this study was to extend the biotyping patterns previously published and usually restricted to some biochemical characters. 192 strains of S. typhimurium, selected as representative of 6 continental French regions and 4 ecological sources, were studied by means of 203 tests, including the assimilation of 147 carbon substrates. An analysis of the results showed that 52 biochemical or nutritional tests could be used as markers during the survey of an epidemic. In addition, 18 of these tests permitted to delineate three polythetic phenons, in which the ecological origin of strains was statistically different. The identification of these phenotypes, before testing markers, could be a useful first step for the investigation of studied strains.

France↗
PubMed1973

Characterization of constitutive galactose permease mutants in Salmonella typhimurium.

Salmonella typhimurium strains, lacking both enzyme I and the phosphocarrier protein, HPr, of the phosphoenolpyruvate-sugar phosphotransferase system, cannot transport or metabolize glucose and other sugar substrates of this enzyme system. Mutants which regain the ability to specifically utilize glucose were found to constitutively synthesize a galactose permease by virtue of a mutation in the galR gene. This permease, shown to be an active transport system, does not require HPr or enzyme I for activity.

Biological Transport, Active↗
PubMed2006

The Acetic Acid Tolerance Response induces cross-protection to salt stress in Salmonella typhimurium.

Salmonella typhimurium induces an Acid Tolerance Response (ATR) upon exposure to mildly acidic conditions in order to protect itself against severe acid shock. This response can also induce cross-protection to other stresses such as heat and salt. We investigated whether both the acetic acid induced and lactic acid induced ATR in S. typhimurium provided cross-protection to a salt stress at 20 degrees C. Acid-adapted cells were challenged with both a sodium chloride (NaCl) and potassium chloride (KCl) shock and their ability to survive ascertained. Acetic acid adaptation provided cells with protection against both NaCl and KCl stress. However, lactic acid adaptation did not protect against either osmotic stressor and rendered cells hypersensitive to NaCl. These results have implications for the food industry where hurdle technology means multiple sub-lethal stresses such as mild pH and low salt are commonly used in the preservation of products.

Acetic Acid↗
PubMed1973

Transport of tricarboxylic acids in Salmonella typhimurium.

Salmonella typhimurium possesses at least three inducible transport systems for the tricarboxylic acids (citric, isocitric, cis-aconitic, and tricarballylic). The first system was induced by citrate, isocitrate, or cis-aconitate, and transported citric acid and isocitric acid. The second system was also induced by the same acids as in the first system and transported cis-aconitic acid. This system required Mg(2+) ions and was stable at pH 8.4 but unstable at pH 7.0. The metal ion was replaced with Sr(2+) or Ca(2+) ions but not with Ba(2+) ions. The third system was induced by tricarballylate and transported citric acid, cis-aconitic acid, and tricarballylic acid.

Aconitum↗
PubMed1989

rfaP mutants of Salmonella typhimurium.

Salmonella typhimurium rfaP mutants were isolated and characterised with respect to their sensitivity towards hydrophobic antibiotics and detergents, and their lipopolysaccharides were chemically analysed. The rfaP mutants were selected after diethylsulfate mutagenesis or as spontaneous mutants. The mutation in two independent mutants SH7770 (line LT2) and SH8551 (line TML) was mapped by cotransduction with cysE to the rfa locus. The mutants were sensitive to hydrophobic antibiotics (clindamycin, erythromycin and novobiocin) and detergents (benzalkoniumchloride and sodium dodecyl sulfate). Analysis of their lipopolysaccharides by chemical methods and by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed that their saccharide portion was, to a large extent, of chemotype Rc with small proportions of material containing a more complete core oligosaccharide and O-specific chains. Only 2.5 mol phosphate/mol lipopolysaccharide was found whereas the phosphate content of the lipopolysaccharide of a galE mutant strain was 4.8 mol. Thus the rfaP mutant lipopolysaccharides lacked more than two phosphate residues. Assessment of the location of phosphate groups in rfaP lipopolysaccharides revealed the presence of at least 2 mol phosphate in lipid A, indicating that the core oligosaccharide was almost devoid of phosphate. The chemical, physiological and genetic data obtained for these mutants are in full agreement with those reported earlier for rfaP mutants of Salmonella minnesota.

Anti-Bacterial Agents↗
PubMed1982

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.

Chromosome Mapping↗
PubMed1981

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.

Mutagenicity Tests↗
PubMed1974

Evidence for the involvement of serine transhydroxymethylase in serine and glycine interconversions in Salmonella typhimurium.

Salmonella typhimurium can normally use glycine as a serine source to support the growth of serine auxotrophs. This reaction was presumed to occur by the reversible activity of the enzyme, serine transhydroxymethylase (E. C. 2. 1. 2. 1; L-serine: tetrahydrofolic-5, 10 transhydroxymethylase), which is responsible for glycine biosynthesis. However, this enzyme had not been demonstrated to be solely capable of synthesizing serine from glycine in vivo. The isolation and characterization of a mutant able to convert serine to glycine but unable to convert glycine to serine supports the conclusion that a single enzyme is involved in this reversible interconversion of serine and glycine. The mutation conferring this phenotype was mapped with other mutations affecting serine transhydroxymethylase (glyA) and assays demonstrated reduced activities of this enzyme in the mutant.

Chromosome Mapping↗
PubMed1984

Biochemical and phenotypical correction of an envelope mutant of Salmonella typhimurium.

Salmonella typhimurium DA 361 bears an env D1 mutation with the following abnormal phenotypical and biochemical characteristics: a) it autolyses at stationary phase in nutrient broth; b) it grows in chains of short rods; c) it is a poor maltose fermenter and d) it has a diphosphatidylglycerol (DPG) content twice as high than its isogenic non-lytic pair DA 362 (env D+) and LT2, of which both are derivatives. Growth of DA 361 in the presence of 400 mM ethanol leads on a 50% decrease of DPG level, thereby equalling its PG/DPG ratio with those of the control strain. Consequently, a correction on the other phenotypical and biochemical anomalies are induced since the DA 361 strain decreases its autolytic activity, ferments normally maltose and appear as rods undifferentiated from DA 362.

Autolysis↗
PubMed1975

Genetic modification of substrate specificity of hypoxanthine phosphoribosyltransferase in Salmonella typhimurium.

Salmonella typhimurium strain GP660 (proAB-gpt deletion, purE) lacks guanine phosphoribosyltransferase and hence cannot utilize guanine as a purine source and is resistant to inhibition by 8-azaguanine. Strain GP660 was mutagenized and a derivative strain (GP36) was isolated for utilization of guanine and hypoxanthine, but not xanthine, as purine sources. This alteration was designated sug. The strain was then sensitive to inhibition by 8-azaguanine. Column chromatographic analysis revealed the altered phosphoribosyltransferase peaks for both hypoxanthine and guanine to be located together, in the same position as hypoxanthine phosphoribosyltransferase (hpt gene product) of the wild-type strain. Genetic analysis showed the sug mutation to be allelic with hpt. Therefore sug represented a modification of the substrate specificity of the hpt gene product.

Alleles↗
PubMed2000

Unravelling the mysteries of virulence gene regulation in Salmonella typhimurium.

Salmonella typhimurium, which causes gastroenteritis in calves and humans as well as a typhoid-like disease in mice, uses numerous virulence factors to infect its hosts. Genes encoding these factors are regulated by many environmental conditions and regulatory pathways in vitro. Many virulence genes are specifically induced at particular sites during infection or in cultured host cells. The complex regulation of virulence genes observed in vitro may be necessary to restrict their expression to specific locations within the host. In vitro and in vivo studies provide clues about how virulence genes might be regulated in vivo. Future studies must assess the actual environmental signals and regulators that modulate each virulence gene in vivo and determine how multiple regulatory pathways are integrated to co-ordinate the appropriate expression of virulence factors at specific sites in vivo.

Animals↗