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Volume 34,
Issue 1,
1964
Volume 34, Issue 1, 1964
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The Effect of Enzyme Treatments on Brucella abortus Cell Walls
More LessSUMMARY: Cell walls of Brucella abortus which were treated with trypsin, ‘Pronase’ (a protease from Streptomyces griseus), or lysozyme were more serologically reactive than cell walls treated with ribonuclease, pepsin or lipase or those with no enzymic treatment. Ribonuclease decreased reactivity of cell wall suspensions. Electron microscopy revealed the presence of round ‘plates’ following treatment with certain of these enzymes. ‘Plates’ were also shown to be embedded in fragments of the cell wall following lysozyme treatment. Still smaller round bodies were also seen to be present. These particles are believed to be a sub-unit of B. abortus cell walls and are correlated with serologic reactivity.
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Kinetic Studies of the Oxidative Assimilation of Acetate by a Non-photosynthetic Strain of Euglena gracilis
More LessSUMMARY: Kinetic studies of the effects of unlabelled acetate on 14CO2 production by a non-photosynthetic strain of 14C-labelled Euglena indicate the existence of a ‘labile reserve’, containing 1.5–2.0 μg.-atom C/million organisms, which is an early product of acetate assimilation and a substrate of endogenous metabolism. When this Euglena assimilated radioactive acetate, radioactivity in an ethanol-soluble form (Soluble I) increased rapidly at first, then levelled off at a value corresponding to about 0.2 μg-atom C/million organisms. Ethanol-insoluble radioactivity appeared slowly at first, then at an increasing rate which became linear at about 30–60 min. after addition of acetate. Kinetic analyses suggest that Soluble I is the precursor of the insoluble material. A second ethanol-soluble component began to become labelled some time after the first hour, and reached maximum radioactivity, corresponding to about 0.5 μg.-atom C/million organisms, 2–3 hr after addition of tracer acetate. The chemical composition of the ethanol-soluble and ethanol-insoluble components and their relationship to the ‘labile reserve’ are discussed.
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Composition of Ethanol-Insoluble Assimilatory Products of Oxidative Assimilation of Acetate by Euglena gracilis
More LessSUMMARY: After incubation for 6 hr. with uniformly labelled 14C-acetate, about 90% of the acetate carbon assimilated by non-photosynthetic Euglena gracilis var. bacillaris was in the form of cellular materials insoluble in 60% (v/v) ethanol in water. Within this fraction about 80% of the assimilated carbon was in the form of glucose units of the polysaccharide paramylon, about 9% was in a fraction containing proteins, nucleic acids and probably other materials, and about 2% was in lipid. The ratio of assimilated carbon to total carbon in the paramylon was 3 to 5 times that in the protein + nucleic acid or lipid fractions.
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Effects of Amino Acids on the Utilization of Tryptophan and Indole for Growth by a Mutant of Neurospora crassa
More LessSUMMARY: Fourteen of twenty-one naturally occurring amino acids inhibited competitively the utilization of tryptophan for growth by an indole- or tryptophan-requiring strain of Neurospora crassa. At less than inhibitory ratios of amino acid to tryptophan, certain amino acids enhanced the growth of this mutant. Growth on indole was neither enhanced nor inhibited by amino acids other than tryptophan. The uptake of tryptophan from the medium was inhibited by phenylalanine. The effects of amino acid on the growth of this strain with tryptophan can be explained by an inhibition of tryptophan uptake from the medium.
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The Occurrence of Muramic Acid in Wax D Preparations of Mycobacteria
More LessSUMMARY: Acid hydrolysates of wax D preparations from human and bovine strains of Mycobacterium tuberculosis were examined by paper chromatography. The amino acids detected in human wax D preparations were alanine, glutamic acid and meso-α, e-diaminopimelic acid. In general, amino acids were not found in bovine wax D preparations. Muramic acid was found in all wax D preparations from human strains of mycobacteria but was not detected in wax D preparations from bovine strains. The presence of this typical cell-wall component, as well as the foregoing amino acids, suggests a close relationship between wax D and the cell-wall mucocomplex. The role of muramic acid in the structure of wax D of human strains of mycobacteria is discussed.
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Some Relations between Chemical Structure and Antifungal Effects of Griseofulvin Analogues
More LessSUMMARY: Inhibitory effects of more than 300 analogues of griseofulvin against six dermatophytic fungi and eight plant pathogenic fungi were determined in an investigation of relations between chemical structure and biological activity. The influence of chemical structure on physical properties of the analogues appeared dominant, but optimum requirements for in vitro performance were somewhat different from those required in vivo for effective control of plant pathogenic or dermatophytic fungi.
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Studies on the Structure of Vaccinia Virus
More LessSUMMARY: Vaccinia virus has been examined with the electron microscope by several techniques in conjunction with experimental modifications of structure. Negative staining revealed that over 80% of the virus in highly purified preparations were particles which appeared to have a beaded surface like a mulberry and were termed M forms. The beading was formed by loops of thread-like structures 90 Å wide which were themselves double helices formed from two 30 Á strands coiled to a 120 Å pitch. Twenty per cent or less of the particles appeared as larger more electron-dense bodies with a capsule of complex structure; these have been termed C forms. Experimental interconversion of the two forms showed that both were structurally mature virus. The relationship of structures seen in C forms to those revealed by thin sectioning is considered. Experimental findings and the results of shadowing and replica examinations indicate the presence of a superficial protein layer of antigenic material not revealed by negative staining. The relationship of this layer to the structure of the virus and the nature of the ribbon structure of the M form are discussed.
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Growth of a Form 2 Mycobacterium and Various Bacillus Species on Löwenstein-Jensen Medium
More LessSUMMARY: Vegetative organisms of a Form 2 strain of Mycobacterium tuberculosis were inoculated on to Löwenstein-Jensen medium containing malachite green. The multiplication of the organisms was slightly delayed by the presence of the dye, but after a few days growth occurred, even when only a few organisms were used as inoculum. Stimulation of growth of Form 2 mycobacteria by the presence of Form 1 mycobacteria was not observed. Spores of Bacillus subtilis and B. licheniformis grew on Löwenstein-Jensen medium. Organisms other than Bacillus were usually obtained from Löwenstein-Jensen medium slopes deliberately exposed to airborne contamination, but have never been found in experiments in which M. tuberculosis Form 2 organisms were isolated. These results establish the validity of the uninoculated control slopes of Löwenstein-Jensen medium used in all previous experiments in which Form 2 mycobacteria were obtained from Form 1 mycobacteria.
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The Nature of the Insensitivity of Gram-Negative Bacteria towards Penicillins
More LessSUMMARY: The insensitivity of Gram-negative bacteria towards different penicillins has been correlated with the inactivation of these compounds by the penicillinases produced by these bacteria. Penicillins such as phenethicillin, propicillin, methicillin, and cloxacillin were relatively inactive against Gram-negative bacteria, but resistance was not accompanied by inactivation of these compounds. With ampicillin and benzylpenicillin, however, bacterial resistance was associated with destruction of the penicillins. Ampicillin was more stable to the penicillinases produced by certain Gram-negative bacteria than was benzylpenicillin and was correspondingly more active against these organisms. Gram-negative bacteria which produced little or no penicillinase were two to four times more sensitive to ampicillin than to benzylpenicillin, but ampicillin was at least ten times more active than benzylpenicillin against several penicillinase-producing coliform organisms. All strains of bacteria which were resistant to both ampicillin and benzylpenicillin were capable of inactivating both compounds, but the insensitivity of these bacteria was not necessarily due solely to penicillinase production. Strains of Pseudomonas aeruginosa and certain strains of Escherichia coli and Proteus mirabilis were able to grow in high concentrations of these antibiotics, whereas with the strains of Aerobacter aerogenes, Proteus morganii and Proteus vulgaris examined, the resistance appeared to be due solely to inactivation of the penicillins.
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Effects of Thermal Stress on Viability and Ribonucleic Acid of Aerobacter aerogenes in Aqueous Suspension
R. E. Strange and M. ShonSUMMARY: The death-rate of washed Aerobacter aerogenes in aqueous suspension at 47° depended on the nature of the growth medium, the composition of the liquid used to wash and resuspend the bacteria, the bacterial growth phase, the bacterial concentration in heated suspensions, the pH value, the oxygen tension and the composition of the diluent in which bacteria were heated. The relative resistance of bacteria in different growth phases differed according to the growth medium and the washing fluid; stationary phase bacteria were not more resistant than exponential phase organisms under all conditions. Starvation increased the thermal resistance of exponential and stationary phase bacteria. High bacterial concentration favoured survival at 47° under most conditions; cell-free filtrate from a heated dense suspension (1010 bacteria/ml.) protected a sparser population of fresh bacteria (107-109/ml.) heated in it. Protective material in filtrate was heat-stable (100°/15 min.) and diffused through cellophan. The optimum pH value for survival at 47° was near pH 6.5. Aerobic conditions favoured survival in distilled water but not in salt solutions or phosphate saline (pH 6.5). The effects of various concentrations of NaCl and KCl on the survival of bacteria at 47° under aerobic conditions were different, K+ concentrations above 0.1 m being more lethal than equivalent concentrations of Na+; the lethal effect of heating in mixtures of these salts (total m > 0.1) increased with K+ concentration. Growth medium, Mg2+ (0.01–5 mm) and, to a lesser extent, Mn2+ (0.5 mm) or Co2+ (5 mm) decreased the death-rate, whereas ethylenediamine tetraacetic acid (mm), or various sugars, increased it. Mg2+ but not Mn2+ reversed the lethal effect of sugars.
Generally, conditions which accelerated the death-rate of Aerobacter aerogenes at 47° also increased the rate of degradation of endogenous RNA. This was accompanied by an increase in the ultraviolet absorption of cold acid-extracts of bacteria and of the suspending fluid. Bacterial protein was degraded to a smaller extent. Depletion of RNA is probably not the primary cause of death at 47° but the effect on bacterial metabolism of a rapid increase in endogenous pool constituents resulting from RNA degradation may contribute to the lethal effect.
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The Chemical Composition of Vaccinia Virus
More LessSUMMARY: Samples of purified vaccinia virus chemically analysed had the following composition (%): N, 14.7; P, 0.49; S, 0.76; DNA, 3.2; total lipid, 5.0 (including cholesterol, 1.2; phospholipid, 2.1); trace constituents detected were: RNA, 0.1; carbohydrate, 0.2; Cu, 0.02; flavin, 5 × 10−4; biotin, 1.3 × 10−5. These results are compared with other published figures and the differences discussed. The trace constituents are not considered to be true components of the virus. On the other hand, there is no evidence for regarding cholesterol and the other lipid components as non-essential constituents of the virus.
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Time-Temperature Interaction in the Induction of Pleomorphism in Trichophyton mentagrophytes
More LessSUMMARY: The frequency of appearance of mutant pleomorphic patches on the surface growth of granular strains of Trichophyton mentagrophytes was markedly increased by incubation at 36° as compared to the number seen at 26°. A minimum of 8–9 days of incubation at the higher temperature was required to induce the higher frequency of pleomorphic mutants and, as the number of days at 36° increased, the number and relative size of the pleomorphic patches also increased. Typical mutants could be isolated whether the granular culture was incubated for 8–9 or 14 days at 36°. Visual scoring was relatively accurate since most of those patches visually scored as pleomorphic were found on isolation to be typical or atypical mutants. Three phenotypic characters were used here to define pleomorphism: type of surface mycelium, pigmentation on reverse side of colony, and effect of methionine. These characters could change independently of one another. Thus, pleomorphism may be the result of alterations in more than one closely linked chromosome-borne locus.
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Relationships between Certain Pyrimidine and Arginine Mutants of Neurospora, as Revealed by their Response to Carbon Dioxide
More LessSUMMARY: A pyrimidine-requiring mutant of Neurospora was found to grow on minimal medium when the proportion of CO2 in the gas-phase (air) was increased to 30% (v/v); arginine prevented growth in 30% CO2, but did not prevent growth when pyrimidines were present. An arginine-requiring mutant also grew on minimal medium in the presence of 30% CO2. The response of this mutant to CO2 was annulled by pyrimidines. It is proposed that these mutants have defects in carbamoyl phosphate synthesis. Wild-type Neurospora may have two pathways for making carbamoyl phosphate from CO2, one pathway subject to feed-back inhibition or repression by arginine, the other pathway subject to feed-back inhibition or repression by pyrimidines. The pyrimidine mutant may lack an enzyme which produces carbamoyl phosphate for pyrimidine synthesis, and the arginine mutant may lack an enzyme which produces carbamoyl phosphate for arginine synthesis. Thus each mutant may have only one effective mechanism for carbamoyl phosphate synthesis. It is suggested that 30% CO2 causes increased synthesis of carbamoyl phosphate by the remaining pathway in each mutant, thereby providing sufficient carbamoyl phosphate to overcome the nutritional deficiency. The inhibition of the pyrimidine mutant by arginine, and the inhibition of the arginine mutant by pyrimidines, are explained as feed-back inhibition or repression of the remaining pathway for carbamoyl phosphate synthesis.
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Physiological Characteristics and Vitamin Requirements of Lactobacilli Isolated from Milk and Cheese
More LessSUMMARY: The vitamin requirements and physiological characteristics of 179 strains of lactobacilli isolated from milk and cheese have been studied and their relationship to classification discussed. The vitamin requirements showed good correlation with the results of the physiological and biochemical tests with strains of the subgenus Streptobacterium but the correlation was poor among the beta bacteria. It was not possible to differentiate the physiologically similar Lactobacillus brevis and L. buchneri species by their vitamin requirements. The nutritional data indicated that the species L. plantarum probably consists of more than one variety, and confirmed the reliability of a thiamine requirement as a means of differentiating heterofermentative and homofermentative lactobacilli. The nutritional data also proved useful with some strains by verifying their unclassifiable status or by making possible their classification when they could not be identified with certainty on the basis of biochemical tests alone. The nitratase activities of strains of L. casei, L. plantarum, L. brevis, L. buchneri and pediococci were also studied. Four of the L. plantarum and 2 of the L. casei strains were able to reduce nitrate but none of the other species tested showed this characteristic.
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The Roles of Serum and Carbon Dioxide in Capsule Formation by Bacillus anthracis
More LessSUMMARY: Capsule formation by virulent strains of Bacillus anthracis on nutrient agar is known to depend on incubation in air with added CO2 as well as the addition of serum or bicarbonate to the medium. The minimum effective concentration of CO2 varies with the pH of the medium in a way which shows that capsulation depends on a threshold concentration of bicarbonate in the medium. Serum is more effective than bicarbonate and appears to act by binding an agent which inhibits capsule formation since it is replaceable by activated charcoal. The inhibitor might be a fatty acid since certain acids prevented capsule formation. Capsules are formed on nutrient agar containing added bicarbonate only after the culture has become very dense which suggests that the organisms either inactivate the inhibitor or become resistant to its action as their growth rate falls on approaching the stationary phase.
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The Cellular Location of Antigens in Streptococci of Groups D, N and Q
More LessSUMMARY: The absence of Group D antigen from the cell walls and protoplasts of Group D streptococci leads to the conclusion that this antigen is located between the protoplast membrane and the cell wall. The Group N antigen was likewise not present in cell walls of Group N streptococci and probably has a similar location to the Group D antigen. The Group Q strains examined possessed the Group D antigen in the cell contents although these strains did not physiologically correspond to any established Group D species. The antigen upon which Group Q is based is a cell-wall antigen.
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