- Volume 72, Issue 2, 1972
Volume 72, Issue 2, 1972
- Biochemistry
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The Effect of Triazole on Cysteine Biosynthesis in Salmonella typhimurium
More LessSUMMARYThe inhibition by triazole of the growth of wild-type Salmonella typhimurium is reversed by serine, methionine or cysteine. Two auxotrophs which responded to any one of these three compounds were hypersensitive to triazole and were shown by genetical analysis and enzyme assays to have a cysE (serine transacetylase) deficiency. Triazole hypersensitivity of the mutants was reversed by sulphite and sulphide and triazole prevented induction of sulphate permease and activating enzymes by O-acetyl serine (OAS) or serine in the wild-type. It is probable that the inhibitory effect of triazole is due to this interference with the induction of cysteine biosynthetic enzymes.
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Neuraminidase and N-Acetylneuraminate Pyruvate-Lyase of Pasteurella multocida
More LessSUMMARYNeuraminidase was found in nearly all strains of Pasteurella multocida, in some strains of P. haemolytica, but not in P. pseudotuberculosis. The enzyme of P. multocida is bound to the bacterial cell. It is inducible by N-acetyl-D-mannosamine and by free and bound sialic acid. After solubilization it has a molecular weight of about 250000, a pH optimum = 6.0, and a Michaelis constant Km = 2 ⨯ 10-4 M when 3’-sialyllactose is used as substrate.
N-acetylneuraminate pyruvate-lyase activity present in Pasteurella multocida is higher in the cell-free culture medium than in the bacterium.
It is suggested that the stimulating effect of blood sera on the production of neuraminidase by Pasteurella multocida is due to the delayed release of the inducer N-acetyl-D-mannosamine.
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- Development And Structure
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Wall Replication in Saccharomyces Species: Use of Fluorescein-conjugated Concanavalin A to Reveal the Site of Mannan Insertion
More LessSUMMARYThe wall mannan in dividing Saccharomyces cells was labelled by exposing the yeasts to fluorescein-conjugated concanavalin A. The yeasts were then allowed to grow in the absence of excess staining reagent and were examined by fluorescence microscopy at several intervals after the re-initiation of growth. The newly synthesized mannan was non-fluorescent and, thus, could be easily distinguished from the material present at the outset. Most new mannan was deposited in the wall surrounding the bud, and little if any of the mannan in the bud wall was derived from the surface of the mother cell. Deposition of new mannan in the mother cell was detected only in the bud scar. The distal tip of the growing bud was identified as the major site at which new mannan was inserted into the existing wall fabric. This area is also known to be the deposition site of newly synthesized glucan. Thus, with respect to these two major wall polysaccharides, wall replication in Saccharomyces cells resembles the apical mode exhibited by filamentous fungi.
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Fine Structure of the Spore Sheath of Some Streptomyces Species
More LessSUMMARYThe fine structure of the spore sheaths of some Streptomyces species was studied by carbon replication of intact and freeze-etched specimens and by negative staining. Young vegetative hyphae lacked a sheath but developed one before the onset of sporing. Substructures were observed on all sheath material; these differed between species and in sporogenous hyphae at different stages of development. Four components were recognized: hollow or grooved elements; amorphous material; fine fibrillar elements; and subunits of spines and hairs. The interrelationships of the components and the possible roles of the sheath were discussed.
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Hydrolysis of Walls and Formation of Sphaeroplasts in Mucor rouxii
More LessSUMMARYWalls from Mucor rouxii were partially lysed by an enzymatic complex present in filtrates from cultures of Streptomyces sp. When germinated spores were incubated with the enzymatic complex in a protective medium, osmotically sensitive sphaeroplasts were formed. The enzyme responsible for the degradation of the wall showed optimum activity at pH 7·5 and 32 °C. It was susceptible to the presence of divalent cations. The enzymatic complex released hexosamines (but no N-acetyl hexosamines), neutral sugars and uronic acids from purified walls of the fungus. A wall-bound α-glucosidase was also rendered soluble by the enzyme. The enzymatic complex hydrolysed chitosan, but not chitin or mucoran, and hydrolysed the walls from only fungi belonging to the Mucorales. It is suggested that the hydrolytic capacity of filtrates from cultures of Streptomyces sp. developed in the presence of walls from M. rouxii was due to an enzyme (chitosanase), acting on chitosan but not on chitin.
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- Genetics And Molecular Biology
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Vegetative Incompatibility and Cytoplasmic Infection in Fungi
More LessSUMMARYThe effect of vegetative (heterokaryon) incompatibility on the transfer of a suppressive cytoplasmically determined condition, vegetative death, from carrier to normal strains of Aspergillus amstelodami has been investigated. Cytoplasmic transfer was reduced to 15 % by vegetative incompatibility compared with 100 % transfer in compatible combinations. Successful transfer in incompatible combinations involved donors and recipients whose incompatibility was determined by a single gene, and transfer was completely prevented between strains differing for more than one incompatibility gene. These results support the hypothesis that vegetative incompatibility serves as a cellular defence mechanism against genetic infection by stopping the spread of viruses and other suppressive cytoplasmic determinants from strain to strain in nature. Vegetative incompatibility is likely to be important in determining the specificity of virus‐host interactions in fungi.
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A Transmissible Resistance Element from a Strain of Pseudomonas aeruginosa Containing No Detectable Extrachromosomal DNA
More LessSUMMARYPseudomonas aeruginosa PS18(RP1) is resistant to carbenicillin, neomycin/kanamycin and tetracycline. This strain gave rise to a derivative: PS18(RP1-1), resistant only to carbenicillin. RP1 was transmissible from PS18(RP1) to other strains of P. aeruginosa, Escherichia coli or Proteus mirabilis while RP1-1 was transmissible to other strains of P. aeruginosa, could not be transferred to Proteus mirabilis and transferred only at a very low frequency to E. coli. DNA hybridization showed that PS18(RP1-1) contained approximately one sixth as much RP1-homologous DNA as PS18(RP1). Although satellite DNA could be detected in strains carrying RP1 by ethidium bromide/CsCl-gradient analysis and by analytical CsCl-gradient centrifuging, no such satellite DNA could be found in strains of P. aeruginosa carrying RP1-1 or E. coli carrying a non-transferable derivative RP1-1*. Drug resistance could be eliminated from RP1-containing strains by treatment with sodium dodecyl sulphate, but the carbenicillin resistance of RP1-1 strains could not be eliminated. The apparent absence of satellite DNA in bacteria carrying RP1-1 or RP1-1*, and the failure to ‘cure’ them of their carbenicillin resistance suggests the possibility that the RP1-1 and RP1-1* genes might be a fragment of RP1 integrated in the chromosome of the strains of P. aeruginosa containing RP1-1 and E. coli containing RP1-1*.
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Shortening of Pseudomonas aeruginosa Pili after RNA-Phage Adsorption
More LessSUMMARYThe F-pilus retraction theory suggests that F-pili retract on contact with a recipient bacterium or pilus-specific bacteriophage, but there has been no direct demonstration of any form of pilus retraction. Electron microscopy is used here to study average length changes in Pseudomonas aeruginosa RNA-phage pili after the adsorption of RNA-phage virions to the sides. The theory predicts that, if one phage per pilus is adsorbed, there should be a reduction of about 50% in the mean length due to the adsorption of virions at random points; retraction would be stopped at the point of adsorption when the virus reached the bacterial surface. A phage-resistant, pilus-bearing P. aeruginosa strain (PAO68), used as a control, showed no such change. The phage-sensitive strain PAOI showed an average reduction in pilus length of about 42.5% relative to its length before adsorption, or 50% relative to the PAO68 average. This strongly suggests pilus retraction in PAOI but not in PAO68. In electron micrographs, phage virions are seen almost always at the bases of PAOI pili, whereas virions adsorbed to PAO68 are randomly distributed along the pili.
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Sensitization to Radiation by Loss of Recombination Ability in a Temperature-sensitive DNA Mutant of Micrococcus radiodurans Held at Its Restrictive Temperature
More LessSUMMARYTwo temperature-sensitive mutants of Micrococcus radiodurans defective in DNA synthesis, which were very resistant to the lethal effect of ultraviolet and ionizing radiation at permissive temperatures, became sensitive to radiation and also to the action of N-methyl-N’-nitro-N-nitrosoguanidine when held at the restrictive temperature of 39 #x00B0;C. With M. radiodurans ts1 the sensitization began soon after transfer to 39 °C and reached a maximum 4 h later. During this period there was no loss of viability. After 4 h the shoulders of the ultraviolet and ionizing radiation survival curves had almost completely disappeared and the exponential part of the curves had doubled in slope. The size of the shoulder fell exponentially with the time the bacteria were held at 39 °C. Sensitization occurred in the presence of chloramphenicol. During the period the bacteria were held at 39 °C their ability to effect recombination as measured by transformation fell exponentially and was correlated with the rate of loss of the shoulder. This suggests that the repair which gives rise to the large shoulders of the radiation survival curves is of the post replication recombination type.
The recovery of radiation resistance at 30 °C in bacteria which had been exposed to 39 °C for 75 min did not begin immediately. For 55 min there was no measurable increase in resistance but after 75 min substantial recovery had occurred and by 105 min was complete. Recovery of resistance did not occur in the presence of chloramphenicol even when the chloramphenicol was added 30 min after the bacteria had been at 30 °C.
The sensitization to radiation was not a general property of temperature-sensitive (ts) mutants.
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Polyene Resistance and the Isolation of Sterol Mutants in Saccharomyces cerevisiae
More LessSUMMARYMutants of Saccharomyces cerevisiae have been selected for resistance to the polyene antibiotics, etruscomycin, filipin, nystatin, pimaricin and rimocidin. All mutants are resistant to nystatin and there are several patterns of cross-resistance. The mutants were allocated to four unlinked genes pol 1, 2, 3 and 5. A fifth gene, pol 4, was recovered as a double mutant with a strain carrying the pol 1 mutation. The pol 4 mutation does not cause resistance, pol 1 and pol 3 are allelic to the previously described nys 1 and nys 3 (Ahmed & Woods, 1967). There are correlations between the polyene used for mutant isolation and (i) the extent of cross-resistance; (ii) the selection of mutants at particular pol genes. Ultraviolet absorption spectra of non-saponifiable material extracted from representative mutants showed that all five genes affect the sterol composition of the cell. The major sterols found in pol + are ergosterol and 24,(28) dehydroergosterol, the latter is not found in any of the mutants whilst ergosterol is lacking in pol 2 and only present at very low levels in pol 3. The spectra of extracts of pol 1 and pol 3 indicate the presence of new sterols (Woods, 1971). Mutants of pol 1 excrete sterol into the growth medium. Studies on double mutants indicate epistasis between pol genes with respect to sterol pattern and suggest that they are metabolically related in the sequence pol 2 → pol 3 → pol 5 → pol 1 → pol 4 → pol +. A rapid qualitative technique for the preparation of non-saponifiable extracts of yeast for sterol analysis is described.
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Trimethoprim Resistance Conferred by W Plasmids in Enterobacteriaceae
More LessSUMMARYHigh-level resistance to trimethoprim (minimum inhibitory concentration > 1000 μg/ml) was conferred by R factors of the W compatibility group in Escherichia coliand Klebsiellaspp. isolated from patients in three London hospitals. We suggest that we are observing the early stages in the spread of a new R factor.
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- Physiology And Growth
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Tryptophan and Indoleacetic Acid Transport in the Olive and Oleander Knot Organism Pseudomonas savastanoi (E. F. Smith) Stevens
More LessSUMMARYTransport studies revealed that Pseudomonas savastanoi readily takes up both tryptophan and indoleacetic acid, and that uptake was pH‐, temperature‐, and energy‐dependent. Uptake of tryptophan and indoleacetic acid appeared to be mediated by separate transport systems on the basis of differences in competitive interactions between tryptophan and indoleacetic acid, kinetics of transport, the pH range, and osmotic shock treatment of cells.
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Effect of Lipid Status on Cytoplasmic and Mitochondrial Protein Synthesis in Anaerobic Cultures of Saccharomyces cerevisiae
More LessSUMMARYSaccharomyces cerevisiae grown anaerobically in the absence of unsaturated fatty acids and sterol depleted its endogenous levels of these lipids by dilution as yeast numbers and mass increased. When the levels of unsaturated fatty acids and sterol reached approximately one-quarter those found in aerobically grown cells, the organisms stopped dividing; cells then ceased generating dry weight. Concomitant with this depletion of lipids was a decline in the protein-synthesizing activity of the cell. In mitochondria this was due to a loss of high molecular weight RNA. In the cytoplasm the effect was at the level of the ribosomes but was not due to loss of integrity of ribosomal or associated RNA, nor to a decrease in the ribosome/polysome complement. When oxygen was supplied, protein synthesis in mitochondria and cytoplasm was rapidly reactivated in the absence of cell growth. This reactivation was accompanied by a rapid resynthesis of unsaturated fatty acids and ergosterol.
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Sterols and the Production of Oospores by Phytophthora cactorum
More LessSUMMARYThe effect of eight sterols on oospore production by Phytophthora cactorum has been studied quantitatively. Their activity was found to be in the following order: β-sitosterol ═▵5-avenasterol═fucosterol═stigmasterol>cholesterol═7-dehydrocholesterol>ergosterol>cholestanol.
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- Short Communication
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