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Volume 13,
Issue 3,
1955
Volume 13, Issue 3, 1955
- Articles
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Further Nutritional Studies of Venturia inaequalis
More LessSummary: A series of nutritional experiments was carried out on cultures from single ascospores isolated from a single ascus of Venturia inaequalis. The results showed: (a) thiamine stimulated all cultures and other vitamins did so to a much less extent; (b) decoctions of apple leaves contained stimulatory substances; (c) these substances were amino acids, chiefly isoleucine, glutamine, serine and phenylalanine; (d) best growth was given by some cultures in the presence of thiamine and various amino acids; (e) the reaction of the fungus cultures to the decoctions, amino acids and thiamine varied according to the cultures and the combination of nutrients. There were indications that the nutritional requirements reflected the genetic composition of a given culture; (f) in the absence of leaf decoctions the best sources of nitrogen were Oxoid peptone and asparagine, and growth with these substances reflected the genetic composition of the organism; (g) at least ten amino acids were shown to be present in the leaves of all or some apple varieties.
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A Multipoint Inoculator for Plating Bacteria or Yeasts
More LessSUMMARY: A multipoint inoculator has been designed for inoculating agar plates with a maximum of twenty-four strains of bacteria or yeasts simultaneously.
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The Cytoloǵy of Bacteroids from Root Nodules of Subterranean Clover (Trifolium subterraneum L.)
More LessSUMMARY: Bacteroids from effective nodules of subterranean clover were ovoid, pear-shaped, or slightly branched and measured 5–7 × 4–6 μ. In the fully developed bacteroid the nuclear material was central, divided into discrete bodies and showed signs of degeneration. Surrounding the nucleus was a perinuclear region, probably derived from it, and this was surrounded by cytoplasm which contained several mitochondria-like granules. The development of bacteroids from rod-shaped cells is described. Bacteroids from the ineffective nodules studied possessed no perinuclear region, and, in contrast to those from effective nodules, accumulated varying amounts of glycogen, depending on the length of time for which the bacteroids survived in the host cell.
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Some Factors Affectinǵ the Formation of Iodophilic Poly-saccharide in Group D Streptococci from the Rumen
More LessSUMMARY: Of 25 isolates of α-haemolytic group D streptococci from the rumens of calves (Mann & Oxford, 1955), 7 produced intracellular iodophilic polysaccharide when grown aerobically or anaerobically in agar media containing starches of various origins, amylopectin, maltose, maltotriose, glycogen, amylose and amylopectin dextrins, or amylose glycollate. The iodophilic polysaccharide was not produced from glucose, sucrose, trehalose, glucose-1-phosphate, glucose-6-phosphate, cellobiose or amylose. These results are discussed in the light of the amylolytic action of the bacteria and known enzymic mechanisms of starch-type polysaccharide formation.
In liquid media the polysaccharide was only produced from maltose when the cells were held at a pH value between 5 and 6, either by adjusting the reaction of the medium after the initial growth period, or by transferring the cells to a maltose solution buffered at the correct pH value and incubating further. Under the correct conditions polysaccharide formation was rapid. The polysaccharide was obtained in a partially purified form from the cells and appears to be unlike most ‘starches’ from bacteria so far reported. A possible explanation of the mode of development of an iodophilic reaction in streptococci in the rumen is given.
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Factors Influencinǵ the Antibacterial Action of Spermine and Spermidine on Staphylococcus aureus
More LessSUMMARY: Spermine and spermidine inhibited the growth of Staphylococcus aureus under both aerobic and anaerobic conditions. The activity of spermine was decreased by sera of different species; sheep and bovine serum showed most effect. This antagonistic effect was destroyed by heating the sera at 100° for 30 min. Sodium and potassium also decreased the antibacterial effect of spermine and spermidine. Spermine exerted a bactericidal effect on staphylococci in broth at 37° and at 6°, but not on washed organisms suspended in buffer at 6°. The dependence of the bactericidal effect of the bases seems to depend on some metabolic activity of the cocci.
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Evidence from the Cytoloǵy of Azotobacter chroococcum of a Relationship with Rhizobium and the Bacillaceae
More LessSUMMARY: The structure of the cell envelopes in Azotobacter chroococcum and the behaviour and mode of formation of the spore-like cysts suggest that this organism has a close phylogenetic relationship with the Bacillaceae, and that accordingly the main genera of nitrogen-fixing bacteria, Azotobacter, Rhizobium, and Clostridium, have a relatively recent common origin.
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Potentiation and Destruction of R Variant Coaǵulase by Products of S Variants of Staphylococcus aureus
More LessSUMMARY: Factors obtained from certain S variants of Staphylococcus aureus can both increase the potency of and destroy the coagulase produced by R variants of the organism. Evidence that separate factors are responsible for potentiation and for destruction of coagulase is based on differences of pH optimum and of temperature range of the factors. Potentiation of coagulase is most marked below pH 7 and occurs at temperatures ranging from 9° to 37°. The optimum pH value for destruction is between 7 and 8, and it does not occur at 9°. There is evidence, though incomplete, that both factors are enzymes. In the course of both potentiation and destruction the mode of clotting by R coagulase is altered from a granular to a solid type. Some properties of the factors and their partial purification are described and their possible mode of action is discussed.
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A Selective Medium for Bacillus anthracis
More LessSUMMARY: A medium containing propamidine is described which has high selective activity for the species Bacillus anthracis. The spore form of the organism is essential as inoculum for the medium.
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Genetic Studies on Small-colony Variants of Escherichia coli K-12
More LessSUMMARY: Stable small-colony variants of Escherichia coli K-12 and several of its auxotrophs were isolated by treatment of cultures with copper sulphate solutions. These variants did not show any associated changes in nutritional, fermentative or serological characters. The small-colony forms showed normal recombining character in two instances, but in one variant the F − form showed a lower recombination rate and atypical transfer of markers. However, when rendered F + this variant behaved in a manner analogous to the normal F + parent strain. The results have been interpreted as evidence that the small-colony character can arise by a nuclear mutation at one of several possible genetic loci.
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The Minimal Nutritional Requirements of Some Species in the Genus Bacillus
More LessSummary: The characteristic nutritional patterns were determined for seven species or varieties of the genus Bacillus. Six strains of Bacillus cereus var. anthracis grew in a complex but defined amino acid medium + thiamine. Three strains of the insect pathogen B. cereus var. thuringiensis had the same nutritional pattern as the parent species B. cereus and grew in a seven amino acid medium. Of twenty strains of B. firmus, ten grew on the seven amino acid medium + biotin while the growth of five other strains was markedly affected by the addition of thiamine. Two of the remaining five strains required thiamine on first isolation, but soon dispensed with it on subculture, while the other three strains continued to require thiamine. Six strains of B. lentus grew in the seven amino acid medium + biotin + thiamine + urea. When the seven amino acid medium was replaced by the complex amino acid medium three of these strains of B. lentus grew without the addition of urea, and the remaining three strains required either urea or ammonium chloride. The sixteen strains of B. coagulans all grew in the complex amino acid medium + biotin + thiamine. The three strains of B. pulvifaciens grew in the seven amino acid medium + biotin.
The twenty-seven strains of Bacillus circulans formed a nutritionally heterogeneous group. Eight strains were maintained in serial subculture in broth but could not be grown in defined media. One strain grew in the ammonia basal medium alone, others required added biotin or added biotin + thiamine and others required amino acid media + biotin + thiamine.
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The Classification of Lactobacilli from the Human Mouth
More LessSummary: A scheme of classification for Lactobacillus strains from diverse sources is proposed, based upon the results obtained with 473 strains, mainly of human oral origin, using a selected range of morphological and physiological taxonomic criteria. Two subgeneric groups, containing five stable and clearly demarcated specific types are recognized.
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Studies on the Multiplication of a Tobacco Necrosis Virus in Inoculated Leaves of French-bean Plants
More LessSummary: By treating leaves of French bean (Phaseolus vulgaris L.) in various ways at intervals after they were inoculated with the Rothamsted tobacco necrosis virus, a series of events in infected cells was detected and approximately timed. Treating leaves with ribonuclease, or floating them in water, in the first hour after inoculation decreases the number of infections; these treatments fail to do so later, perhaps because the virus has become firmly attached to some host component, or because cells injured at inoculation have healed and no longer allow virus particles to diffuse out or ribonuclease in.
After 2 hr. at 25° the virus is less readily inactivated by ultraviolet radiation than previously, suggesting that infected cells now contain more of substances that absorb radiation of 2537A. After 4 hr. the inactivation curve with ultraviolet radiation deviates from the course of a first-order reaction, probably because some infected cells now contain more than one potentially infective particle. After 6 hr. the formation of some lesions cannot be prevented by irradiation, suggesting that newly formed virus has spread from initially infected cells to deeper tissues, where it is protected from inactivation. At 16° the mean time for virus to spread from the initially infected cells is 12·5 hr. and it probably spreads from some cells by 8 hr. and from most by 15 hr.
Newly formed virus is not detectable in extracts of inoculated leaves until after it has spread from the epidermis to deeper tissues. Up to 20 hr. after inoculation most of the extractable virus seems to come from the epidermis, but later it comes predominantly from other tissues.
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The Mode of Action of Antibiotic Synergism and Antaǵonism: the Effect in Vitro on Bacteria not Actively Multiplyinǵ
More LessSUMMARY: The synergistic effect of certain pairs of antibiotics might be due to action on ‘persisters;’ i.e. members of a bacterial population which survive exposure to single drugs, perhaps while in a state of reduced metabolic activity, although their offspring do not show enhanced resistance. Hence, antibiotics were tested in vitro under conditions minimizing bacterial multiplication and metabolism. At 37°, neomycin, polymyxin, and streptomycin were more effective in the absence of nutrients than in nutrient broth; oxytetracycline and bacitracin were equally effective in either environment; but penicillin had little effect in the absence of nutrients. At 4°, bactericidal action varied with the test organism so that differences could not be attributed solely to the ‘resting’ state of the bacteria. Conditions not permitting bacterial multiplication prevented synergism and those antagonisms demonstrable in broth. Probably synergism depends upon rapid bactericidal action preventing the emergence of persisters rather than upon destruction of these relatively inactive forms.
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The Influence of the Factors Determining Vi-type Specificity in Salmonella typhi on the Adaptation of Vi-phaǵe II
More LessSummary: All adaptations of Vi-phage II to the known Vi-types of Salmonella typhi have been grown on Vi-type A. In confirmation of earlier work these adaptations were found to be phenotypic or genotypic modifications of the original Vi-phage II, or showed a combination of both changes. Most adaptations to non-lysogenic types are changes of phenotype only, whereas those to lysogenic types are usually genotypically stable, although they may have a superimposed phenotypic modification. The fact that Vi-types that are exactly similar to naturally occurring types can be made artificially by the lysogenization of non-lysogenic types with type-determining phages makes it possible to assign structural formulae to most of the known naturally occurring Vi-types. The formulae consist of the symbol of the non-lysogenic precursor of a lysogenic type followed by that of the type-determining temperate phage in parenthesis. Thus, type F2 is type F1 carrying phage f2 and the formula of type F2 is therefore F1(f2). Using these formulae it is possible to predict the host range of Vi-phage II adapted to each lysogenic Vi-type. The phenotypic and genotypic changes concerned in the many adaptations of Vi-phage II are independent of one another, and by taking advantage of this independence it is possible to adduce experimental proof of the correctness of the proposed structural formulae for the lysogenically determined Vi-types. In studying the Vi-types it is useful to regroup those that are lysogenic according to the non-lysogenic precursor types common to certain of them.
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The Stability of Lactobacillus Strains
More LessSummary: Reported changes of pure strains of Lactobacillus from the hetero-fermentative to the homofermentative type, with concomitant changes in many characters of recognized taxonomic importance, were investigated. No evidence was obtained that such gross variations occur. Inadequate initial purification and subsequent contamination between strains of different physiological types, were found to produce effects which could be mistaken for such changes.
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Studies on Cytophaga fermentans, n.sp., a Facultatively Anaerobic Lower Myxobacterium
More LessSummary: A previously undescribed myxobacterium was isolated from marine mud and studied in pure culture. This organism is a typical non-fruiting, amicro-cystogenous lower myxobacterium and has been classified in the genus Cytophaga under the name C. fermentans, n.sp., to indicate its ability, unique among the cytophagas so far studied, to grow anaerobically at the expense of organic compounds. The organism can utilize as carbon and energy sources simple sugars and starch, but not cellulose, agar or chitin. Ammonium salts, asparagine or glutamine are satisfactory nitrogen sources; urea, nitrates and amino acids are not. Thiamine and relatively high concentrations of iron and CO2 are required for growth in a defined medium. Glucose is fermented to acetic, propionic and succinic acids, in approximately equimolar quantities, plus a small amount of lactic acid. In addition, a large quantity of mucilage, which appears to be a nitrogen-containing substance, is produced during the fermentation.
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Amino Acid Metabolism in the Genus Bordetella
More LessSummary: Bordetella pertussis, B. parapertussis and B. bronchiseptica all grow in an amino acid medium, using glutamate and forming ammonia from it. After the glutamate has been used, B. pertussis and B. parapertussis deaminate aspartic acid, serine, glycine, alanine and proline. B. bronchiseptica, as well as these amino acids, deaminates threonine, valine, methionine, the leucines and phenylalanine, leaving only histidine, lysine and arginine. B. bronchiseptica grows the most rapidly of the three and B. pertussis the most slowly. All three organisms oxidize glutamate to give CO2 and ammonia but in each some nitrogen is unaccounted for. B. bronchiseptica contains a glutamic decarboxylase and B. parapertussis forms a pink pigment from tyrosine.
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Proof of the Spontaneity of a Mutation to Penicillinase Production in Bacillus cereus
More LessSUMMARY: A stable mutation in a strain of Bacillus cereus from penicillin sensitivity to penicillin resistance due to the production of large amounts of penicillinase is reported. By the velvet pad replicate technique this mutation has been shown to be a spontaneous event occurring in the absence of penicillin. Penicillin-resistant mutants were obtained and the penicillinase production proved, without ever bringing the cells into contact with the antibiotic. The mutation rate is about 3 × 10−8 mutations per bacterium per division.
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Four New Diphasic Members of the Arizona Group of Bacteria found in Reptiles
More LessSUMMARY: Four hitherto undescribed diphasic members of the Arizona group of bacteria were identified in reptilian faeces. These organisms appear to occur frequently in healthy Constrictor constrictor.
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Genetic Recombination in Pseudomonas aeruginosa
More LessSUMMARY: Genetic recombination has been shown to occur in Pseudomonas aeruginosa. Crosses between 18 biochemical mutants of 4 strains were studied and, although non-random segregation was found for non-selective markers, it has not yet been possible to draw conclusions concerning gene order or linkage. The progeny obtained from crosses tended to resemble one parent more than the other. The 4 strains of P. aeruginosa used were interfertile in certain combinations but self-sterile. There was no evidence for an infectious principle affecting fertility but fertility changes may occur amongst recombinant progeny.
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