- Volume 85, Issue 1, 1974
Volume 85, Issue 1, 1974
- Biochemistry
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Some Properties of a Bacterial Protease with a Specific Effect on the Protein in Tobacco Rattle Virus Particles
More LessSUMMARY: A pseudomonad bacterium contaminating a preparation of purified tobacco rattle virus was isolated. It produced proteolytic enzyme activity in nutrient broth + 1 % glucose; activity was greatest in the stationary phase of growth. This enzyme acted on the protein in particles of tobacco rattle virus to produce a polypeptide that migrated more rapidly in sodium dodecyl sulphate-acrylamide gels than untreated virus coat protein. The estimate of molecular weight of the modified protein was less affected by gel strength than that of the unmodified protein. The enzyme appeared as a single component when analysed by polyacrylamide gel electrophoresis or by gel filtration in Sephadex G-100; its apparent molecular weight was about 45000. Enzyme activity did not require added thiol reagents, but was reversibly inhibited by EDTA.
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- Development And Structure
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Ultrastructure of a Marine Thiobacillus
More LessSUMMARY: The ultrastructure of Thiobacillus sp. IV-85 was examined by thin section and freeze-etch techniques. The morphology of this marine isolate was similar to that of terrestrial species of Thiobacillus. Decline phase preparations showed a marked degeneration of internal organization. Membrane vesicles, characteristically bound by a trilaminar membrane, were observed only in preparations of decline phase cells. The examination of freeze-etched preparations of both first and second log phase organisms showed membrane-bound polyhedral inclusion bodies in intact cells and a characteristically rippled envelope.
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Growth and Encystation of Acanthamoeba castellanii
More LessSUMMARY: Complete encystment of Acanthamoeba occurred in peptone-yeast extract-glucose medium supplemented with 50 mM-magnesium chloride. There was an increase in the RNA, protein and DNA contents of the cells which coincided with an increase in the proportion of binucleate amoebae and commitment to encystation, suggesting that encystation could be a consequence of the inhibition of cell division when nutrient concentrations were limiting growth.
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- Ecology
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Fungal Growth Rate and the Formation of Ethylene in Soil
More LessSUMMARY: The rates of ethylene production per unit mass of Mucor hiemalis are highest at low specific growth rates. Thus this fungus probably produces more ethylene in the soil, where growth rates are low, than would have been predicted by laboratory batch culture, where growth rates are high. The rate of utilization of energy-yielding substrate by Mucor hiemalis increases logarithmically with growth rate. This contrasts with the data obtained for Penicillium digitatum and Aspergillus nidulans; it is discussed in terms of the success of Mucor hiemalis as a primary saprophytic sugar fungus.
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Nitrogen Fixation by the Rumen Contents of Sheep
K. Jones and J. G. ThomasSUMMARY: Assays using 15N2 and acetylene reduction showed that bacteria in the sheep rumen can fix atmospheric nitrogen. These bacteria are ingested when sheep are at pasture or provided with fresh, non-sterile, food. A permanent nitrogen-fixing microflora does not develop in the rumen. The addition of nitrogen-fixing bacteria to sheep rumina coupled with additional carbohydrate (10% molasses) in the feed increased the nitrogen-fixing capacity from 30 mg N to 800 mg N fixed/rumen/day.
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- Genetics And Molecular Biology
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The Genetic Analysis of Resistance to Benomyl in Neurospora crassa
More LessSUMMARY: Mutants of Neurospora crassa resistant to the fungicide, methyl-1-(butyl-carbamoyl)-benzimidazolecarbamate, were isolated following u.v. irradiation of conidia. Genetic analysis of 15 of the mutant strains revealed that resistance was due to a single allele averaging 2·9 map units right of ylo-1, 17·9 units right of tryp-2 and 32·1 units left of chol-2 in linkage group VI. Tests of heterokaryons containing both resistant and sensitive alleles indicated that resistance is dominant. The mutants did not possess the same degree of tolerance to the fungicide.
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Polynucleotide Sequence Relationships among Plasmids of the I Compatibility Complex
More LessSUMMARY: Plasmids determining I pili show a variety of intricate compatibility relationships. None the less, all I plasmids tested showed a ‘core’ of common DNA sequences of approximately 30 x 106 daltons. Plasmids of the O compatibility group do not appear to specify for the synthesis of I-like pili and yet they held about 20 % of their sequences in common with all tested I plasmids, suggesting a common phylogenetic origin. Members of the I complex (including group O) do not hold a significant proportion of their sequences in common with representative plasmids of other compatibility groups. We propose that the regions of similar polynucleotide sequences of the different I complex plasmids are due to phylogenetic homology between genes governing pili biosynthesis and/or transfer functions. The regions determining compatibility of the I complex plasmids in some cases may be either unrelated to or have diverged from a common ancestor.
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Pseudomonas aeruginosa Mutants Defective in Heptane Oxidation
More LessSUMMARY: Fourteen mutants of Pseudomonas aeruginosa ATCC 17423, isolated for their inability to grow rapidly on heptane while still growing normally on heptanoic acid, were all also able to grow on heptanol or heptanal. A study of heptane oxidation in extracts showed differences between the mutants, which were resolved into four groups (A to D). Group A or B alone could not oxidize heptane, but a mixture of the extracts was effective, and either A or B stimulated the slight activity of extracts from group D mutants. Extracts from group C mutants were inactive in virtually all circumstances. The mutants therefore lack, in different ways, one or more of the three components demonstrated to be necessary for heptane oxidation, but no mutant totally lacking rubredoxin was demonstrated.
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Envelope Alterations Produced by R Factors in Proteus mirabilis
More LessSUMMARY: R-1818 increases swarming and abolishes proteolytic enzyme excretion by P. mirabilis F67. R-TEM reduces swarming, increases proteolytic enzyme excretion by this organism and renders it susceptible to sodium deoxycholate. The properties of strains harbouring both R-1818 and R-TEM simultaneously are dependent on the order of introduction of the R factors, the R factor first present being dominant. Recombination between the R factors in this organism does not seem to be responsible for these observations.
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- Physiology And Growth
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Yeast Mutant Requiring an Organic Solvent for Growth
F. Karst and F. LacrouteSUMMARY: A mutation has been found which makes yeast dependent on either organic solvents or high temperature for growth. This phenotype suggested an impairment in lipid mobility, but a chemical analysis has disproved this hypothesis. A study of the physiology of the mutant shows an impairment in RNA biosynthesis. This may be due either to a primary effect of the mutation or, more probably, to a secondary effect through regulation.
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Nitrite and Ammonia Assimilation by Anaerobic Continuous Cultures of Escherichia coli
More LessSUMMARY: Anaerobic continuous cultures of Escherichia coli strains Hfrc and K12-OR75 assimilated nitrite to produce 63·7 g dry mass/g-atom N. Washout occurred when these cultures were aerated, or when the dilution rate was above 0·05 h−1. Nitrite reductase, glutamate dehydrogenase and glutamine synthetase activities and cytochrome c 552 synthesis were derepressed when growth of strain OR75 was limited by the concentration of either nitrite or ammonia in the reservoir. Glutamate synthase activity was far less than glutamate dehydrogenase, but was highest when nitrite limited growth. These results indicate that enzymes which catalyse glutamate synthesis from inorganic nitrogen compounds are regulated in an interdependent manner, but that glutamine synthetase protein is unlikely to be the aporepressor for glutamate dehydrogenase synthesis in this organism. Possible reasons for apparently opposite regulatory mechanisms in E. coli and Klebsiella aerogenes are discussed in the context of the selective pressures which are applied to bacteria in continuous culture. We conclude that E. coli K12 has alternative pathways for synthesizing glutamate, and because the K m of glutamate dehydrogenase for NH3 is 1·6 mM, a growth-limiting concentration of an inorganic nitrogen compound in the reservoir would be assimilated predominantly by the glutamine synthetase-glutamate synthase pathway.
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The Utilization of Nitrogen Sources by Aspergillus clavatus
More LessSUMMARY: Ammonia, urea and glutamate are each used as sole nitrogen source by germinating conidia of Aspergillus clavatus. Ammonia is used preferentially when provided in the medium together with urea or glutamate. Germinated conidia actively transport glutamate against a concentration gradient. The suppression of glutamate utilization by ammonia is possibly mediated by an effect on the transport system for glutamate.
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Regulation of Aromatic Metabolism in Fungi: Selection of Mutants of the Yeast Rhodotorula mucilaginosa with Nystatin
More LessSUMMARY: The antifungal antibiotic nystatin has been successfully used to select mutants of the yeast Rhodotorula mucilaginosa from populations consisting largely of wild-type organisms. The most efficient selection technique has been found by a study of the duration of the nitrogen starvation period, the composition of the starvation medium, and the concentration of nystatin. Several mutants have been obtained which are unable to utilize either or both of the aromatic carbon sources p-hydroxy- benzoate and protocatechuate.
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Regulation of Aromatic Metabolism in the Fungi: Metabolic Control of the 3-Oxoadipate Pathway in the Yeast Rhodotorula mucilaginosa
K. A. Cook and R. B. CainSUMMARY: The metabolic control of the protocatechuate branch of the 3-oxoadipate pathway in Rhodotorula mucilaginosa was examined and the specific inducers identified using appropriately blocked mutants. Three successive inductive events permitted the synthesis of the five enzymes converting p-hydroxybenzoate to 3-oxoadipyl-CoA: the independent induction of 4-hydroxybenzoate 3-mono-oxygenase by its own specific substrate, the independent induction of protocatechuate 3,4-dioxygenase by either protocatechuate or p-hydroxybenzoate, and finally the co-ordinate induction of 3-carboxymuconate cyclase, 3-carboxymucono-lactone hydrolase and 3-oxoadipate CoA-transferase by cither protocatechuate or p-hydroxybenzoate. Evidence is presented which suggests that R. mucilaginosa is unable to metabolize catechol or its usual precursors, and the significance of this is discussed in relation to control of the protocatechuate branch and the differing control mechanisms governing the synthesis of enzymes of the 3-oxoadipate pathway in other fungi and bacteria.
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Diterpenes from Nicotiana glutinosa and their Effect on Fungal Growth
More LessSUMMARY: The diterpenes sclareol and 13-epi-sclareol were isolated as a eutectic mixture from leaves of Nicotiana glutinosa. These compounds were probably present in liquid droplets which occurred on the leaf surface. These diterpenes did not prevent germination of fungal spores but markedly inhibited the radial extension of colonies growing on agar. This inhibition is shown to be due to an effect on the morphology of the fungi in which the degree of hyphal branching is increased. The possibility that sclareol/13-epi-sclareol influence the growth-regulatory processes of fungal hyphae and the potential of these compounds to affect growth of fungi on the surface of leaves of N. glutinosa is discussed.
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The Effects of β-Galactosidase Activity and Cyclic AMP on Lactose-accelerated Death
More LessSUMMARY: Lactose-limited chemostat populations of Klebsiella aerogenes 418 showed hyper-β-galactosidase activity after 170 generations. Within the normally active phase, hyperactivity could be induced by adding thiomethyl-β-d-galactoside and was lost on its removal; natural hyper-activity was lost on transfer to a lactose medium in which ammonium was limiting. The ability of lactose to accelerate death from starvation was proportional to the β-galactosidase activity of the population. Cyclic AMP in the recovery medium alleviated lactose-accelerated death. Suppression of adenyl cyclase activity by traumatic substrates may be responsible for substrate-accelerated death.
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Growth Inhibition of Acetobacter aceti by L-Threonine and L-Homoserine: the Primary Regulation of the Biosynthesis of Amino Acids of the Aspartate Family
More LessSUMMARY: Growth of Acetobacter aceti NCIB8554 was inhibited by l-threonine and l-homoserine. Inhibition was relieved by l-aspartate, l-methionine or l-isoleucine. Aspartokinase was inhibited by l-threonine or l-lysine and concertedly inhibited by the two together. l-Methionine or l-threonine. Acetobacter aceti possesses one aspartokinase and a separate homoserine dehydrogenase. Neither enzyme is subject to repression by amino acids of the aspartate family.
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- Short Communication
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- Taxonomy
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Characterization of Some Caprine Mycoplasmas, with Proposals for New Species, Mycoplasma capricolum and Mycoplasma putrefaciens
More LessSUMMARY: Of a group of unclassified, mostly caprine mycoplasmas, six were antigenically related to one another, possessed similar biochemical and biological properties and were anticenically distinct from all other human and animal Mycoplasmatales. It is proposed that this group of mycoplasmas be established as a new species within the Mycoplasmatales. One additional isolate, of questionable host origin, was also antigenically distinct from other Mycoplasmatales and is proposed as another new species. The identification of mycoplasmas originally recovered from porcine and caprine hosts as Mycoplasma mycoides subsp. mycoides supports recent evidence that this subspecies occurs in animals other than cattle. The results emphasize the importance of using proper type strains of M. mycoides subsp. mycoides and M. mycoides subsp. capri in serological identification of mycoplasmas recovered from animal hosts.
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