- Volume 36, Issue 3, 1964
Volume 36, Issue 3, 1964
- Article
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Studies of Methionine Synthesis in Coprinus lagopus
More LessSUMMARY: When methionine was present in the growth medium of wild-type Coprinus lagopus the incorporation of isotope from 35S-sulphate into both cysteine and methionine was greatly decreased. Under these conditions much of the cysteine formed must have arisen from methionine and it is concluded that the diminution of cysteine synthesis from sulphate is caused by the cysteine formed from the methionine and not directly by methionine itself.
Wild-type Coprinus accumulated large amounts of cystathionine when grown with methionine and this appeared to have arisen from the added methionine as isotope from 35S-sulphate was not incorporated into the accumulated compound. The cysteine formed from methionine may have been formed from this accumulated cystathionine.
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O-Succinylhomoserine as an Intermediate in the Synthesis of Cystathionine by Escherichia coli
More LessSUMMARY: Further evidence that cystathionine is a precursor of methionine synthesis in Escherichia coli was obtained by showing its synthesis by cell- free extracts of an auxotroph which required homocysteine or methionine for growth. Succinate, as well as homoserine and cysteine, was an obligatory substrate and maximal synthesis was dependent on the further addition of glucose, adenosine triphosphate and coenzyme A. The reaction was further studied by using mixtures of extracts of auxotrophs of which each alone was unable to synthesize cystathionine. At least two enzymes were required: the first, present in one strain, formed a heat-stable intermediate from homoserine and succinate; while the second, present in the other strain, converted this intermediate to cystathionine in the presence of cysteine. The intermediate was formed enzymically from homoserine and succinyl-coenzyme A alone and was ninhydrin-positive; this suggested that it might be O-succinylhomoserine. This compound was prepared by reaction of succinyl chloride or succinic anhydride with homoserine in the presence of perchloric acid; its chromatographic and chemical properties were closely similar to those of the intermediate. The synthetic product, like that formed enzymically, gave cystathionine when incubated with cysteine and a cell-free extract of the relevant E. coli auxotroph. It is concluded that O-succinylhomoserine is an intermediate in the formation of cystathionine, and consequently of methionine by E. coli.
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Attraction Through Air Exerted by Unaggregated Cells on Aggregates of the Slime Mould Polysphondylium violaceum
More LessSUMMARY
In darkness the unitary, elongated aggregates, or grex, of Polysphondylium violaceum are strongly attracted through air to earlier stages of development, including pre-aggregation and feeding cells. Hence the factor responsible cannot be acrasin. This attraction is dominant over mutual grex repulsion. The significance of the response is obscure. Dictyostelium discoideum cells also attract P. violaceum grex, but do not appear to attract culminating D. discoideum grex.
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Transfer of the Colicin I Factor in Escherichia coli k12 and its Interaction with the F Fertility Factor
More LessSUMMARY: A series of Escherichia coli k 12 strains of various mating types was made resistant to colicin I (colI-r) and colicinogenic for this character (colI +). In the absence of the F sex factor, the number of ‘competent donors’ of colI in broth cultures of colicinogenic strains was about 1 %. Transfer of colI to non-colicinogenic strains reached about 7–10 % within 2 hr of mixing, and between 50 and 100 % after incubation overnight. Cells newly infected with colI transfer more efficiently, and can infect over 90 % of a recipient strain with colI within 1 hr of mixing (high-frequency colicino-geny transfer, HFC). When the F factor was present in the colicinogenic donor strain of a mixture, colI transfer was reduced; when F was present in the non-colicinogenic recipient, colI transfer was increased. The colicin I factor appeared to be transferred by a series of Hfr strains as an extrachromosomal element.
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The Regulation of Colicin Synthesis and Colicin Factor Transfer in Escherichia coli K 12
More LessSummary: Cells of Escherichia coli, newly infected with the colicin I factor (colI), showed an enhanced efficiency of transfer of this factor (HFC), and were also more likely to undergo lethal colicin synthesis, than were stably colicinogenic cells. Up to 20% of the cells of stably colI + strains were induced to produce colicin by ultraviolet irradiation, and from such irradiated cultures transfer of the colI factor occurred more efficiently. To account for these results, it is proposed that the colI factor exists as an autonomous non-chromosomal genetic element which sets up its own system of self-regulation within cells of stably colicinogenic strains.
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Penetration of Substances into Cold-Shocked Bacteria
More LessSUMMARYThe death-rate of washed exponential phase Aerobacter aerogenes chilled in saline phosphate buffer (pH 6·5) at 0° was increased by ribonuclease (RNase) but not by deoxyribonuclease, trypsin, pepsin or lysozyme; noneof these enzymes had any immediate effect on the viability of similar bacterial suspensions at 20°. Leakage products from chilled A. aerogenes, Mg2+ and, to a smaller extent, 0·3 m-sucrose, antagonized the lethal effect of RNase on chilled organisms. RNA degradation occurred when bacteria were chilled and then incubated in fresh diluent at 37°; organisms exposed to RNase during chilling degraded RNA at 20–25° when the rate of autodegradation of RNA was low. As the salt content of the environment was decreased, the amount of RNase adsorbed by the bacteria and its lethal effect increased at both 0° and 20°; in distilled water RNase was more lethal at 20° than at 0°. Anilino-naphthalene-8-sulphonate penetrated into bacteria chilled in buffer containing this dye. Acid or alkali accelerated the death rate of bacteria to greater extents at 0° than at 20°. RNase increased the lethal effect of freezing and thawing on a population from a continuous culture and augmented subsequent degradation of RNA.
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Azelaic Acid Utilization by a Pseudomonas
More LessSummary: A Pseudomonas isolate which utilizes azelaic acid as the sole carbon source was isolated from garden soil. Two different variants of the microorganisms were obtained from the original culture in azelaic acid medium. One variant (s), exhibited uniform turbidity which clarified rapidly after maximal growth was obtained. The second variant (T) grew in aggregates and clumps. Both variants gave normal growth curves with a maximal stationary phase in medium with glucose or in azelate medium with high osmotic pressure. The double role of azelaic acid as a source of carbon and as a harmful agent is discussed. It was concluded that when the concentration of azelate is low enough and its action not prolonged it caused cytological disturbances which were not easy to observe (variant s). But the prolonged action of azelaic acid resulted in phenotypical changes that were partially inheritable even in its absence (variant T).
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Nitroǵen Fixation by Myxophyceae from Marine Environments
More LessSUMMARY: Two blue-green algae from marine environments, Calothrix scopulorum and Nostoc entophytum, vigorously fixed 15N-labelled nitrogen in artificial sea-water free from combined nitrogen and, rather faster, in natural seawater. A proportion of the nitrogen fixed was liberated into the medium. After a 7-day exposure period the extracellular nitrogen had a lower enrichment with 15N than the intracellular nitrogen. Fixation rates were not markedly affected by large variations in salinity of the medium. Calothrix was more resistant to changes in salinity than was Nostoc. Fixation in sea-water collected at various seasons was highest in January samples and lowest in July samples; additions of phosphate and of trace elements to the latter stimulated fixation. Ammonium-nitrogen did not inhibit fixation completely. It is probable that these species fix some nitrogen in Nature.
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Genetic Analysis of Oxytetracycline Resistance in Bacillus subtilis by means of Transformation
More LessSUMMARY
Mutants of Bacillus subtilis resistant to oxytetracycline were produced and DNA prepared from them was then used for transforming a sensitive strain. DNA from a first-step mutant seemed to transmit a single genetic factor.
On the other hand, bacteria, transformed with DNA from a second-step mutant, showed a trimodal distribution of resistance, suggesting that at least two factors were involved in the process. Transformation with DNA from clones belonging to the first and second peaks of the distribution showed that such clones transmitted a single genetic factor for oxytetracycline resistance, while DNA from clones of the third peak transformed sensitive bacteria in a way similar to that of the second step mutant. The results suggested that the two factors are linked and that they had a cumulative effect on drug resistance.
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Farmer’s Lung Disease: the Development of Antigens in Moulding Hay
More LessSUMMARY: Antigens important in farmer’s lung disease (FLH antigen complex) developed in wet hay ( ⩾30 % water content) 4–6 days after baling; their development was associated with increases in pH value of the hay, in content of soluble and volatile nitrogen, and in numbers of actinomycetes, bacteria and fungi. Most of the antigens were common to the actinomycetes Thermopolyspora polyspora and Micromonospora vulgaris, but others were unidentified. Brown hay from a self-heated stack contained no FLH antigen except where actinomycetes and fungi had developed and the pH had risen from 4·5 to near 7·0.
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Composition of the Mucopolymer in Cell Walls of the Unstable and Stable L-Form of Proteus mirabilis
More LessSUMMARY: Continuous, cell-shaped mucopolymer layers were isolated from cell walls of some unstable and stable L-forms of Proteus mirabilis. The chemical compositions of these non-rigid mucopolymers and of normal rigid mucopolymer basal-structures of rod-shaped Proteus bacteria were very similar. Electron microscopy showed that the protein and mucopolymer of the complex ‘rigid layers’ were organized differently in cell walls of rods and L-form cells. The results suggest that the rigid-layer protein plays a role in the morphogenesis of the mucopolymer.
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Factors Influencing Osmotic Fragility of Mycoplasma
More LessSUMMARYOsmotic lysis of Mycoplasma organisms was found to depend on the temperature of incubation. The organisms were practically resistant to osmotic shock at 0°, but lysed rapidly at 37°. Their sensitivity to lysis also depended on the pH value of the suspending medium, being lowest at pH values near neutrality. Divalent and polyvalent cations, in concentrations as low as 10−5 m, protected my coplasmas from osmotic lysis. The parasitic Mycoplasma strains showed various degrees of osmotic fragility, Mycoplasma gallisepticum being the least fragile. All the parasitic strains tested were, however, more resistant to osmotic lysis than the saprophytic Mycoplasma laidlawii. The possibility that osmotic lysis of my coplasmas involves autolytic processes was tested and is discussed.
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The Significance of Bacteriophage in Bacterial Classification
More LessSummary: A given race of phage grows in a relatively limited range of bacteria. A coli phage, for instance, will not lyse a staphylococcus or a corynebacterium. Within these limits, however, some phages have a much wider host-range than others: some attack only one or a few bacterial strains; some a whole species; and some can lyse members of several species which on other grounds are considered to be not too distantly related. For instance, some pasteurella phages also attack strains of Salmonella and Shigella (Lazarus & Gunnison, 1947). The phage-sensitivity of a strain as a basis for bacterial classification can be interpreted in two ways, just as there are two levels at which bacterial classification can itself be regarded. That is to say, either as just another phenotypic character which the two strains may have in common; or at the level of the genetic material, the nucleic acid, so that, if two bacterial strains interact with the same phage at the genetic level, each of the strains is manifesting some degree of genetic compatibility with the phage, and thus with each other.
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