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Volume 26,
Issue 3,
1961
Volume 26, Issue 3, 1961
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The Occurrence of Polythionates as Intermediates in the Metabolism of Thiosulphate by the Thiobacilli
More LessSUMMARY: Further evidence for the inclusion of polythionates in the pathway of thiosulphate oxidation by members of the genus Thiobacillus is presented. Manometric experients showed tetrathionate oxidation to be a stage in thiosulphate oxidation by tspensions of T. thioparus and T. thiocyanoxidans. Thiobacillus thioparus accumulated a sufficient concentration of polythionate in the medium to allow chromatorams to be prepared, and the type of polythionate accumulated was influenced by the ratio between the sodium and potassium ions in the medium. The restriction of the oxidation of tetrathionate at the lower concentrations of K+ may be due to a restriction in the entry of phosphate into the cell during growth; this is discussed.
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On the Survival of Frozen Bacteria
More LessSUMMARY: Steadily growing Aerobacter aerogenes organisms were largely killed by slow freezing in buffer or by freeze drying. 100% survival was obtained after dropping bacteria suspended in 10% aqueous glycerol into liquid nitrogen and thawing. Ten per cent solutions of diethylene glycol, i-erythritol, glucose, sucrose or polyethylene glycol (MW = 10,000) protected equally well; the last three substances did not penetrate the cell cytoplasm. The most lethal medium was dilute NaCl; broth, water or a dilute salt mixture were moderately lethal. These findings are incompatible with the view that the lethal effects of freezing are connected with osmotic shock or that protection from freezing damage requires (a) penetration of the protective agent or (b) osmotic dehydration of the cytoplasm. Cells frozen and thawed, even with a protective agent, showed a lowered rate of glycerol oxidation and a higher death rate when starved at the optimal temperature and pH value for growth. The storage life of frozen organisms at −20° depended on the protective agent used; only glycerol permitted extended storage.
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A Comparison of Methods for Classifying Rhizosphere Bacteria
More LessSUMMARY: A comparison was made between the following three methods of classifying bacteria: (1) division on associated characters, (2) identification by the use of Skerman's key, (3) classification by means of Affinity Index. Division on associated characters was of no value in this particular case. Skerman's key was adequate for the identification of the isolates, while the Affinity Index (a slight modification of the Similarity Index of Sneath) gave a comprehensive view of the relationships between isolates. It was considered that a random sample of 43 isolates selected from a collection of 318 rhizosphere bacteria formed a spectrum, rather than a series of groups.
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RNA Synthesis and Degradation during Antibiotic Treatment and its Relation to Antibiotic-induced Lag
More LessSUMMARY: When growing cells of Escherichia coli were treated with chloramphenicol or erythromycin for 1 hr. and then suspended in antibiotic-free medium, there was a 45 min. lag before growth resumed. By eliminating growth factors or other essential nutrients during antibiotic treatment, it was possible to show that the lag occurred only when ribonucleic acid (RNA) synthesis could take place and did not require the synthesis of deoxyribonucleic acid (DNA). This antibiotic-induced RNA was apparently abnormal and was degraded when the antibiotic was removed. This degradation is a hydrolytic process and does not require the presence of a complete growth medium. During the recovery from the antibiotic-induced lag, DNA and protein synthesis did not occur, but RNA synthesis occurred, even though this new RNA synthesis was not required for the lag to be overcome. When antibiotic-treated cells were suspended in phosphate buffer, a decrease in optical density of the suspension occurred which resembled a lytic process, but lysis apparently did not occur. Although these results clarify considerably earlier observations on antibiotic-induced lag, they leave unsolved the question of why the antibiotic-induced RNA is abnormal, and how it brings about the lag.
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Some Properties of a Cytopathogenic Bovine Orphan Virus (Van den Ende Strain)
More LessSUMMARY: A cytopathogenic bovine orphan (CBO) virus isolated from a bovine with lumpy skin disease appears unrelated to any of the three groups of viruses now associated with this condition. The virus multiplies efficiently in cultures of whole chick embryo tissue and may be titrated by plaque counting methods. Tissue culture fluids contain infective particles of at least three sizes, with sedimentation constants of 460, 72 and 20 S. The intermediate particle, if spherical and lipid free, would be comparable in size to the virus of foot and mouth disease. Heterogeneity of the virus has also been demonstrated by plaque morphology, electrophoresis and chromatography on DEAE cellulose. It is adsorbed to fresh but not to receptor-destroying enzyme (RDE) treated red cells of chicken and goose, but haemagglutination has not been observed with cells of any of the species tested. The virus lacks enzyme activity comparable to that of influenza virus.
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Neutralization of a Cytopathogenic Bovine Orphan Virus in Tissue Culture by Heat Stable Francis Type Inhibitors in Normal Animal Sera
More LessSUMMARY: A heat stable inhibitor present in the serum of normal animals was found to neutralize the infectivity of a cytopathogenic bovine orphan (CBO) virus. Its distribution and some physical, chemical and biological properties were examined. These properties suggest that the inhibitor for the virus infectivity is similar to, but not identical with Francis type inhibitors in normal animal sera.
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Titration of Trachoma Virus with Observations on Yolk-sac Infection and Sensitivity to Oxytetracycline, using the Single-dilution method
More LessSUMMARY: The T'ang strain of trachoma virus was titrated in chick embryo yolk sac by a single-dilution method (Golub, 1948), using 3-6 eggs/dilution. The limitations incurred by the use of small numbers of eggs are discussed. The method was used to make observations on the fate of virus after inoculation into the yolk sac, and to study the sensitivity of virus to oxytetracycline. The method was found to be unsuitable for titration of neutralizing antibodies in fowl serum.
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Influence of Certain Sterols and 2:4-Dinitrophenol on Phosphate Accumulation and Distribution in Tetrahymena pyriformis
More LessSUMMARY: Orthophosphate accumulation by Tetrahymena pyriformis W was enhanced by stigmasterol, β-sitosterol or cholesterol and depressed by 2:4-dinitrophenol (DNP) to an extent determined by the concentration of DNP and hydrogen ion in the suspension medium. The depression of phosphate accumulation by DNP was mitigated by the addition of stigmasterol, the degree of annulment being dependent in part on the stigmasterol concentration. The distribution of accumulated phosphate was not significantly altered by the addition of sterol and/or DNP under the conditions used, indicating that these compounds may influence entry of ortho-phosphate by affecting a membrane phenomenon.
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The Type A Phages of Salmonella typhimurium: Observations on Temperate Phage and Lysogenesis
More LessSUMMARY: When a standard suspension of Salmonella typhimurium Q1, an indicator strain sensitive to the type A phages recovered from lysogenic strains of this organism. was exposed to concentrations of these phages giving a phage:bacteria ratio of approximately 1:10 (thus ensuring that, with rare exceptions, bacteria became infected with single phage particles) it was found that definite percentages of the bacteria were either lysogenized or productively infected (lysed). These percentages were constant for each particular phage type, but varied widely in the 11 members of the group. It was concluded that each phage consisted of a mixed population of particles, some capable, as single infections, of producing lysogenization (α particles) and others lacking this property (β particles). An increase in the phage: bacteria ratio, resulting in multiple infections of single bacteria, led to an increase in lysogenization at the expense of productive infection. The number of α particles present in any particular concentration of phage was calculated from the figures determined at low phage:bacteria ratios (limit dilution). With some phages, when bacteria became infected with more than one particle by exposure to rising phage concentrations, the number lysogenized was compatible with the hypothesis that α particles are dominant over β particles, and that every bacterium infected by an α particle is lysogenized. This hypothesis was however invalidated by the fact that, with other phages, either the number of bacteria lysogenized was in excess of the available α particles, indicating that bacteria had been lysogenized by infection with two or more β particles, or the number of α particles was grossly in excess of the number of bacteria lysogenized. The implications of these findings are discussed.
Very high concentrations of these temperate phages produced lysis-from-without, and in some cases appeared to induce lysis of bacteria which had first been lysogenized. In all cases in which such experiments were carried out, exposure to low temperatures (20°), to high temperatures (42°), to the salts of certain organic acids, and to anaerobiosis had no significant effect on lysogenization.
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The Effect of N-Ethylmaleimide on the Radiation Sensitivity of Bacteria
More LessSUMMARY: The sensitization of Escherichia coli strain B/r to γ radiation was shown to take place within a few minutes of the addition of N-ethylmaleimide. Sensitization was demonstrated with as little as 0.0001 m-N-ethylmaleimide, but a much higher concentration (> 0.002 m) was necessary for any bactericidal effect. The N-ethyl-maleimide had to be present during irradiation in order to be effective. Staphylococcus aureus and a Pseudomonas sp. but not spores of Bacillus subtilis, were also sensitized by N-ethylmaleimide. The Pseudomonas sp. was only sensitized under anoxic conditions; this may indicate that, with this organism, N-ethylmaleimide and oxygen acted competitively in enhancing radiation damage. Possible mechanisms of sensitization are discussed.
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The Nature of the Widespread Soil Fungistasis
More LessSUMMARY: Fungistasis of Conover loam, muck, and hardwood forest soils to conidia of Glomerella cingulata, Fusarium oxysporum f. lycopersici, and Penicillium frequentans was demonstrated by indirect methods such as agar disks, double agar layer plates, and cellophan folds, as well as by direct placement of spores on or in soils. All attempts to extract toxic substances from soil with water or organic solvents failed. Fungistatic volatile substances could not be demonstrated in soil. Redox, pH, and osmotic conditions were not responsible for soil fungistasis. Various lines of evidence led to the conclusion that the so-called widespread soil fungistasis as observed by indirect methods is the result of production of antibiotics by soil microbes growing on the surface of the assay media, and is not due to a reserve of toxic substances in soils. The possibility is suggested that individual fungus spores serve as nutrient microsubstrates in soil and stimulate the rapid growth of soil microbes on their surface or in their immediate vicinity, and that this results in the production of sufficient fungistatic substances to prevent spore germination. Preliminary evidence in support of this suggestion are results with concentrated 50% ethanol washings from teliospores of Ustilago zeae which markedly stimulated growth of mixed soil microbes and of pure cultures of Streptomyces sp. and Pseudomonas sp., known antibiotic producers, in agar media.
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Physiology of the Conjugation Process in the Yeast Hansenula wingei
More LessSUMMARY: The yeast Hansenula wingei is a favourable organism for study of the physiology of the conjugation process (cell fusion). Microscopic observations on fusion are presented which reveal that the mating cells in contact fuse by a softening of the cell wall, followed by formation of a conjugation tube, dissolution of the cross-walls between them, and formation of a new bud at the point of juncture of the two cells. A simple technique for studying fusion in a liquid medium is described. Up to 80% of the cells will fuse in 5 hr. at 30† in a medium containing an energy source, MgSO4 and potassium phosphate, under conditions in which no growth or budding of unmated cells would occur. Synthesis of new protein is required for fusion as shown by inhibition by amino acid analogues. The precursors for this new protein come from the amino acid pool. Both mating types must be able to function for conjugation to occur. It is postulated that each mating type produces an inducer which diffuses into the opposite type. Each inducer brings about the synthesis of a wall-softening enzyme which acts upon the cell producing it. Cell fusion is viewed as an extension of the normal budding process.
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Illegitimate Mating in Paramecium bursaria and the Basis for Cell Union
More LessSUMMARY: Cells from stock Wu-67 of Paramecium bursaria, syngen 1, can be induced to conjugate inter se (self) if they have made brief but transitory contact with cells of a complementary mating type; in mixtures consisting of marked cells of Wu-67 and cells of a complementary mating type both interclonal and intraclonal (Wu-67 x Wu-67) conjugations were recognized. Unmixed cultures of Wu-67 never self nor could selfing be induced in other ways. In contrast to normal conjugation the intraclonal matings are illegitimate because they occur between cells expressing a common mating-type specificity. These and other facts are considered in light of Weiss's hypothesis about cell unions; it is postulated that a primary specific surface reaction dependent upon mating-type complementarity serves to elicit a secondary non-specific (‘holdfast’) reaction leading to the completion of conjugation. In cells from Wu-67 the sites of secondary reaction are held to be precociously or more readily activated than in normal cells and, when two such activated cells are apposed, illegitimate mating may occur. Under certain circumstances then, cellular adhesion and conjugation may be independent of primary mating-type complementarity and dependent instead upon the availability of secondary non-specific attachment sites.
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Resistance and Cross-resistance of Escherichia coli Mutants to Antitumour Agent Mitomycin C
More LessSUMMARY: The cross-resistance patterns are described for 96 mutants selected in one step from Escherichia coli strain S for resistance to Mitomyein C. The test agents used were ultraviolet radiation, seven radiomimetic and two non-radiomimetic compounds. Seven different types of mutants could be selected in one step from the parent. Five of these were radioresistant; two were chemoresistant. Of the radioresistant types two were identical with types previously isolated using other radiomimetic agents for selection; three of the types were new. One of the new types was reactivated by plating medium following ultraviolet irradiation differently from all other radioresistant mutants of E. coli S. One of the chemoresistant types was resistant only to Mitomycin C; the other displayed a low degree of cross-resistance to nitronitroso-guanidines and to penicillin. Also described are the cross-resistance patterns of mutants selected in five consecutive steps for increasing resistance to Mitomycin C. Beginning with a first step radioresistant mutant it was possible to select four additional steps, up to 325-fold, in resistance to Mitomycin C. One of these steps appeared to be a shift from one radioresistant type to another.
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The Role of Polygalacturonase in Root-Hair Invasion by Nodule Bacteria
More LessSUMMARY: The production of polygalacturonase in associations of nodule bacteria and seedlings of leguminous plants was investigated. Plants and bacteria were combined in the following ways: (a) different plant species were combined with infective strains (isolated from the same cross inoculation group) as well as non-infective ones (from foreign groups); (b) host plant species with different susceptibilities were combined with the same bacterial strain; (c) bacterial strains with different in-fectivities, as measured by the number of infection sites, were combined with the same host species; (d) clover strains which had lost their infectivity, as well as transformed and again infective subcultures of these strains, were tested on clover plants. The results indicate that infection of the seedlings was strongly correlated with the production of polygalacturonase. The conclusion is drawn that polygalacturonase plays an important part in the infection process. This function is thought to be a weakening of the cell wall of the root hair which would facilitate the bacterial invasion. The possible role also of indolyl-3-acetic acid in the infection process is discussed.
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The Isolation of [35S]Homocystine from Neurospora
More LessSUMMARY: Evidence is presented inferring accumulation of [35S]homocysteine in methionine-less mutants of Neurospora crassa. Certain mutants formed five times as much homocystine as did the wild type; [35S]homocysteine was identified as homo-cystine and homocysteic acid.
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The Relationship of the Enterobacterium A 12 (Sachs) to Shigella boydii 14
More LessSUMMARY: The relationship of the enterobacterium A 12 (Sachs) to Shigella boydii 14 is shown by comparison of their biochemical and serological reactions. The aerogenic, mannitol-negative A 12 is serologically identical with the typical Shigella serotype, S. boydii 14. As mannitol-negative strains of S. boydii 14 exist and as the aerogenic A 12 organism is otherwise biochemically typical of the Shigella group, it is proposed that A 12 be regarded as a biochemical variety of S. boydii 14 analogous to the accepted aerogenic biochemical varieties of S. flexneri 6.
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