- Volume 25, Issue 3, 1961
Volume 25, Issue 3, 1961
- Article
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The Characterization of Pseudomonas fluorescens with the Aid of an Electronic Computer
More LessSUMMARY: Data which had been used to characterize the species Pseudomonas fluorescens (Rhodes, 1959), as distinct from the data used to define the genus Pseudomonas, have now been used to obtain an assessment of the over-all similarity of 169 isolates of polarly flagellate bacteria (mainly of the P. fluorescens species-group) by means of an electronic computer. The results of this analysis are compared with the arrangement of isolates previously favoured by the author. It was found that the two arrangements were often closely similar; the discrepancies are discussed. The two aeromonads of the collection were picked out by the computer, which also satisfactorily replaced an accidentally misplaced pseudomonad isolate. One hundred and thirty-four isolates previously considered to belong to the P. fluorescens species-group were positioned together by the computer in a group with more than 80·0% over-all similarity throughout. This confirmed previous conclusions about the validity of this taxonomic unit, even though the description of it may appear imprecise because each character was not possessed by every isolate. The possibility of further species differentiation within this group is discussed, particularly with regard to P. aeruginosa. The results suggest that P. aeruginosa may be regarded as a variety of P. fluorescens. Other evidence was obtained which suggests that further work on the phytopathogenic pseudomonads may well reveal significant differences from P. fluorescens. Factors governing the choice of a type strain or culture are discussed.
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Association of a Serum Opacity Reaction with Serological Type in Streptococcus pyogenes
More LessSUMMARY: Krumwiede (1954) reported that some group A streptococci formed a lipoproteinase which was capable of producing opalescence in horse serum. A survey of a large number of strains of group A streptococci has shown that those strains which carry an easily identifiable M antigen rarely produce the serum opalescence reaction, except for Types 2 and 9. On the other hand those types that elaborate M antigen poorly or not at all are usually good producers of the serum opacity reaction.
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Form and Internal Structure of Cellular Aggregations in Early Escherichia coli Microcultures
More LessSUMMARY: A critical examination of results obtained with several microculture techniques showed that considerable variations may occur in the formation of cell aggregations, localized in definite zones in the preparation. The cellular aggregation studied in the greatest detail was the clonal microcolony. Time-lapse photomicrography of developing Escherichia coli microcolonies revealed that the arrangement of organisms follows an orderly pattern in both the smooth and rough phases. The genealogical history of the microcolony showed that cells are grouped by genealogical origin. The microcolonial configuration in both smooth and rough phases, at room temperature and 87°, consisted of closely packed arrays of organisms. At these temperatures, palisading appeared to be the primary movement through which the structure of the microcolonies was established. The usual palisading movement was of the sliding type, although buckling palisades were occasionally found in rough-phase cultures. At 44°, the microcolonial configuration in both smooth and rough phases did not invariably evolve through palisading. In these aberrant cases, the organisms appeared simply to push each other about, so that the final appearance was that of a loosely packed collection of organisms presenting as an irregular reticulum. Nevertheless, genealogical distribution remained orderly.
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The Effect of Light on the Developmental Cycle of Nostoc muscorum, a Filamentous Blue-Green Alga
More LessSummary: The Allison strain of Nostoc muscorum, when cultivated in complete darkness, differs morphologically from the forms which prevail in the light. When cultivated in the dark with glucose as energy and carbon source, the alga grows very slowly as a mass of large undifferentiated cells (the aseriate stage). Exposure to small amounts of light or the addition of aqueous extracts of light-grown cells enables development of typical nostocacean filaments. The aseriate morphology is a transient stage of development found in all autotrophic or photoheterotrophic cultures. By growing Nostoc in complete darkness and then exposing to light of low intensity, synchronous development occurs. The cyclic sequence of development is described. The inhibition of growth in the dark is interpreted as a lack of morphogenetic substances formed only in the light.
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Cultivation and Serial Transfer of the Slime Mould, Dictyostelium discoideum in Liquid Nutrient Medium
More LessSummary: A method is described for the routine cultivation and serial passage of the slime mould Dictyostelium discoideum in liquid medium in association with Aerobacter aerogenes. The growth rates of several strains have been measured under these conditions.
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Pseudomonas—An attempt at a ǵeneral classification
More LessSUMMARY: On the basis of the characterization of 126 strains representing 46 different species of Pseudomonas and 6 species of Aeromonas obtained from different culture collections, a proposal for the taxonomy of the genus Pseudomonas is made. By using various old and new diagnostic methods some 90 different morphological and cultural characters, many obtained by modification of methods and media, were investigated. The iodoacetate test was developed to distinguish between oxidative and fermentative utilization of glucose.
Results were evaluated by the use of punched cards and by the method of strips. The relationships between the established species of Pseudomonas and Aeromonas were shown by using an Adansonian principle and by taxonomic models. On the basis of the results obtained proposals for the definition of the genus Pseudomonas and for re-descriptions of Pseudomonas species are given and the relations to related genera are shown. In the definition of the genus Pseudomonas an attempt to find a more general principle for subdivision within the genus was based on the type of glucose utilization and on the relationships of the species expressed in some other features. This proposal about the taxonomy of pseudomonads is compared with that of Rhodes (1959).
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Lysoǵeny and Colicinogeny in Escherichia coli
More LessSUMMARY: One hundred and eighty-three strains of Escherichia coli were examined for lysogeny and colicinogeny: 40·4 % were neither lysogenic nor colicinogenic; 31·1 % were only colicinogenic; 13·1% were only lysogenic; 15·2% were lysogenic and colicinogenic. Though the detection of lysogeny could almost certainly be increased by using a greater number of sensitive indicator strains or by using more sensitive methods, the results of this study suggest: (a) that lysogeny in E. coli is more frequent than found in earlier studies (Fredericq, 1952); (b) that lysogeny and colicinogeny are not correlated but occur independently in E. coli strains.
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Induction of Malic Enzyme and of Oxalacetate Decarboxylase in Three Lactic Acid Bacteria
More LessSUMMARY: The presence of inducible, DPN-specific malic enzymes have been demonstrated in Lactobacillus plantarum, L. casei and Streptococcus faecalis. Of 30 compounds tested, only l-malate induced the synthesis of malic enzyme in L. plantarum.
The possibility that the malic enzymes of these three organisms are bifunctional proteins which have separate sites to decarboxylate oxalacetate has been excluded. In addition to l-malate, three compounds, oxalacetate, acetoacetate and α-keto- glutarate, induce the synthesis of oxalacetate decarboxylase even though they cannot induce the synthesis of malic enzyme. The oxalacetate decarboxylation system consists of an oxalacetate decarboxylase and an oxalacetate permease. Malate can induce the synthesis of only oxalacetate decarboxylase and not oxalacetate permease.
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The Effect of Environment on the Replication of Poliovirus in Monkey Kidney Cells
More LessSUMMARY: Poliovirus can complete its maturation in monkey kidney cells suspended in semi-solid agar. Infectious particles and the progeny from each infected cell diffuse through the semi-solid agar to form a single plaque in an underlying monkey kidney cell monolayer. Using this technique, the effect of environment on the multiplication of poliovirus in singly infected monkey kidney cells was studied. Under optimal conditions of pH and temperature (pH 7·0–7·4, 37°) one-step growth curves indicated that over 95% of the adsorbed virus particles went into eclipse; that the eclipse phase lasted 3–4 hr.; that the increase in infective virus was exponential and that a yield of 700–1400 infectious particles/infected cell was obtained in 12–14 hr. After about 10 % of the total progeny had formed, the cells began to release virus. Under suboptimal conditions of pH or temperature, the eclipse stage was prolonged. At pH 6·0–6·5 it lasted for 6 hr. and at pH 5·0–5·5 for more than 9 hr. At 25° virus particles were adsorbed and went into eclipse, with the exception of some particles which remained infectious and could be neutralized by antiserum. Thereafter the eclipse stage was strikingly prolonged, and replication proceeded on raising the temperature to 37°.
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Reduced Oxidative Activities in Escherichia coli and Bacillus megaterium in Relation to Other Chanǵes durinǵ Inhibition of Growth by Streptomycin
More LessSUMMARY: When the growth of cultures of Bacillus megaterium KM, Escherichia coli B or Bacillus subtilis ceased following addition of streptomycin during the exponential phase of growth, harvested organisms showed oxidative activities on glucose, lactate, pyruvate and succinate which were between 20 and 60 % of those of normal organisms. With E. coli, this reduction in oxidative activity was closely parallel to the decrease in growth rate. During the period in which growth became fully inhibited by streptomycin, the total quantities of amino acids and 260 mμabsorbing compounds in hot water extracts of E. coli and B. megaterium did not differ significantly from those in normal organisms. Protoplasts could be prepared in normal yield from streptomycin-inhibited organisms of both these species ; such protoplasts showed normal stability and had internal osmotic pressures which differed only slightly from normal. From these results it appears unlikely that there was any general breakdown of the permeability barrier of these organisms during inhibition of growth by streptomycin. Lysates of protoplasts from streptomycin- inhibited Bacillus megaterium showed oxidative activities which were also decreased to between 20 % and 45 % of those of lysates from normal organisms. With succinate and malate as substrates this difference appeared to be due predominantly to a considerable decrease in the activity of the sedimentable ‘ghost’ fraction of the lysed protoplasts.
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Ability of S-Methyl-l-cysteine to Annul the Inhibition of Yeast Growth by l-Ethionine and by S-Ethyl-l-cysteine
More LessSUMMARY: The inhibition of growth of a brewer’s yeast and four other yeasts by l-ethionine, and the annulment of the inhibition by l-methionine were examined. S-Methyl- l-cysteine, dl-methionine sulphoxide and dl-α-amino-n-butyric acid were also able to decrease the growth inhibition. At a fivefold molar concentration, S-methyl cysteine annulled completely the effect of ethionine on the brewer’s yeast. S-Ethyl- l-cysteine was ineffective and in certain conditions it acted as a growth inhibitor; this inhibition was annulled by methionine and by S-methylcysteine.
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The Action of Phospholipase A and Lipid Solvents on Murray Valley Encephalitis Virus
More LessSUMMARY: Phospholipase A (100 µg./ml.) acting at 37° for 30 min. decreased the infective titre of crude or purified Murray Valley encephalitis (MVE) virus from 7 or 8 log to less than 1 log. This inactivated virus yielded 2 log of infective ‘ ribonucleic acid ’ (‘RNA’) when it was treated with phenol. Ether, chloroform or butanol acting at 0–4° each decreased the infectivity of crude or purified MVE virus. Again the inactivated virus yielded ‘RNA’ with an infective titre higher than the titre of the inactivated virus. Infective ‘RNA’ prepared from crude MVE virus was not inactivated by ether, chloroform or butanol. High concentrations of phospholipase A preparations destroyed ‘RNA’, possibly due to traces of contaminating ribo-nuclease. The results suggest that intact viral phospholipid is necessary for infectivity of the virus particle.
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Activation of one Tobacco Necrosis Virus by Another
More LessSUMMARY: Preparations of the Rothamsted culture of tobacco necrosis virus always gave two and usually three zones when centrifuged in sucrose density gradients. The top zone consisted of polyhedral particles with a sedimentation constant of 50 S, the middle zone of larger polyhedral particles with 116 S, and the bottom zone when present, consisted of the 50 S particles aggregated in groups of 12. Neither the small particles (50 S) nor their aggregates were infective when inoculated either to tobacco or French bean plants, but they became so when inoculated together with the large particles (116S). The small and large particles are serologically unrelated and seem to be different viruses, one of which depends on the other for some process that allows it to multiply to detectable amounts.
The Rothamsted culture produces local lesions of different sizes in French bean. Virus isolated from single large lesions and passed through a succession of single lesions gave, when bulked in tobacco, preparations containing up to 500 large to 1 small particle. Evidence is given which suggests that the few small particles were acquired as contaminants when the virus was bulked in tobacco, and it seems probable that small particles would not be produced in leaves infected only with the large particles. Virus obtained from small lesions when bulked gave preparations containing particles of both sizes, with ratios of large to small particles up to 1:10. Inocula of large particles produced only large lesions, whereas mixed inocula produced large and small lesions, in proportions which depended on the ratio of the two kinds of particles in the inoculum. Two different tobacco necrosis viruses activated the small particles, but tobacco mosaic and some other viruses did not.
Particles of the two activating viruses differed in size and in their stability when negatively stained in phosphotungstate. When fixed and negatively stained they appeared to be angular, but much less so than when shadowed. Small particles tended to pack in regular arrays, and one type of packing suggested that they have a fivefold axis of symmetry.
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Correlation of the Vitamin Requirements with Cultural and Biochemical Characters of Lactobacillus spp
More LessSUMMARY: Improved media are described for the study of the vitamin requirements of a wide range of Lactobacillus spp., some of which had not previously been grown consistently well. In general, the nutritional data are consistent within species and correlate well with the other differentiating characteristics of species. Also, the nutritional requirements were in agreement with results obtained with several species some years ago. Improved or abundant growth, not achieved in previous studies with several other species, resulted from the use of the more nearly optimal media developed in the present study. The growth of L. bulgaricus was prevented or inhibited by folic acid at 10 μg./l.
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The Air Spora of a Cowshed
More LessSUMMARY: Study of the air spora of a cowshed by means of a Hirst Automatic Volumetric Spore Trap showed an atmospheric concentration of fungal spores ranging from 95,000 to 16,000,000 spores/m3. There was a direct relationship between the hours during which hay was being fed and the highest concentrations of spores. Asper-gillus-Penicillium and Mucor types of spore were predominant, and hyphal fragments including conidiophores were the third most numerous component. The findings are discussed with reference to human and animal fungal disease.
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