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Volume 79,
Issue 1,
1973
Volume 79, Issue 1, 1973
- Obituary
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- Sgm Special Lecture
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- Biochemistry
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Utilization of Some Tricarboxylic-acid-cycle Intermediates by Mitochondria and Growing Mycelium of Aspergillus terreus
More LessSUMMARY: Mitochondria of Aspergillus terreus nrrl 1960 and two mutants, 25/iii and β, were not able to oxidize tricarboxylic-acid-cycle intermediates, either in the presence of ADP or cytochrome c, or after disruption of mitochondrial membranes. Reduced pyridine nucleotides, in particular NADH, were the only substrates respired. In the presence of NADH without added ADP the oxygen uptake was from 14 to 55 ng-atom oxygen/min/mg protein, while with ADP it was from 21 to 130 ng-atom O/min/mg protein, with respiratory control ratios from 1.8 to 2.9 and ADP/O ratios from 0.8 to 1.8. The lowest consumption of oxygen was shown by the mutant 25/iii dissimilating nitrate as the source of nitrogen.
The cultures converted malate to itaconate and succinate, fumarate to itaconate and one unknown acid, and pyruvate to all the acids usually produced in glucose media. Succinate, citrate, lactate, propionate and acetate supported growth without acid production.
It is concluded that the synthesis of itaconate in Aspergillus terreus is probably not via the tricarboxylic acid cycle.
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The Acidic Amino-acid Permease of Aspergillus nidulans
More LessSUMMARY: A single permease is responsible for the active transport of l-glutamate, l-aspartate and l-cysteate in Aspergillus nidulans. Apparent Km values are 180 μ m, 100 μ m and 190 μ m respectively. The transport of glutamate occurs against a concentration gradient of at least 1:200, is inhibited by azide and cyanide, and shows a pH optimum of 5.0 and a temperature optimum of 45 °C.
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Regulation of the Acidic Amino-acid Permease of Aspergillus nidulans
More LessSUMMARY: Conidia of Aspergillus nidulans transported the acidic amino acids and some basic and neutral amino acids at very low rates. During germination the rates of transport of these amino acids increased. The rate of permease synthesis/litre of culture increased during germination, reaching a maximum soon after onset of exponential growth; during subsequent growth the rate of synthesis (per litre of culture) was constant.
The activity of the acidic amino acid permease, measured in germinated conidia, varied with the nitrogen source in the germination medium. An analysis of the intracellular pool of amino acids has shown no clear correlation between activity of the permease and the intracellular concentration of any amino acid.
The acidic amino-acid permease of Aspergillus nidulans is probably regulated by ammonia from within the organism and this regulation is achieved by both inhibition and repression.
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The Control of Homoserine-O-transsuccinylase in a Methionine-requiring Mutant of the Blue-green Alga Anacystis nidulans
More LessSUMMARY: The regulation of the first step in methionine biosynthesis, homoserine-O-transsuccinylase, has been examined in a methionine-requiring mutant of the blue-green alga Anacystis nidulans. Using an improved assay for homoserine-O-transsuccinylase, no evidence of derepression of the biosynthesis of this enzyme was found, even under conditions of acute methionine starvation. End-product inhibition of the enzyme by homoserine, cystathionine and methionine was demonstrated, and shown in the latter case to be of an allosteric nature. The lack of transcription control of this enzyme is discussed as an example of a general phenomenon in this group of micro-organisms.
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- Development And Structure
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A Comparative Ultrastructural Study on Conidium Differentiation in the Cladosarum-like Mutant 22b of Aspergillus aureolatus
More LessSUMMARY: The ultrastructure of conidium formation in a wild-type, and in a temperature-sensitive and osmotic-remedial strain of Aspergillus aureolatus has been studied. In the mutant 22b the development of true conidia was blocked at non-permissive conditions. The conidial chain elongation was basipetal in the wild-type and apical in the mutant. The result of the apical elongation was a simple or a branched chain of undifferentiated conidia, encompassed by a thin single-layered non-pigmented wall, which were limited by septa with open pores. The last, or two last, elements in the chain were potential conidia, because if the temperature was lowered they could develop into true conidia. Their wall could complete the process of thickening and appeared three-layered. The outer wall layer acquired ornaments and pigment, and the septal pore was occluded.
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Goblet-shaped Sub-units from the Wall of a Marine Gliding Microbe
More LessSUMMARY: Goblet-shaped sub-units from the wall of a gliding marine bacterium have been isolated. They are apparently largely proteinaceous, having a buoyant density in CsCl solution of 1.31 g/ml at 25 °C. Their ultrastructure revealed by electron microscopy allows the hypothesis that they function in vivo as secretory organelles.
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Ultrastructural Studies on Selenomonas ruminantium from the Sheep Rumen
More LessSUMMARY: The sheep rumen micro-organism Selenomonas ruminantium was studied in preparations of rumen contents by light- and electron-microscopic techniques.
The fascicle of entwined flagella, which is often found curled-up close to the cell body, arises from a specialized organelle derived from the cell cytoplasm and cell membrane. This organelle has presumably developed from the ‘polar organelle’ specialization of the cell membrane already described for Spirillum, but in Selenomonas the organelle is situated directly behind the flagella instead of beside them. For this reason we use the distinguishing term ‘flagellar organelle’.
Other structural peculiarities include flagellar fibres with unusually large diameter (20 nm) and 11-fold radial symmetry, an electron-dense layer adhering to the cell membrane in the region of the polar organelle, and an abundance of finger-like cytoplasmic processes projecting into an amorphous matrix beneath the layers of the cell wall.
The taxonomic status of S. ruminantium is briefly considered in the light of these results.
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- Ecology
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The Incidence of the Genus Myrothecium in New Zealand Pastures and Its Relation to Animal Disease
More LessSUMMARY: Four species of Myrothecium, in descending order of frequency Myrothecium leucotrichum, M. verrucaria, M. cinctum and M. roridum, occurred on leaves of perennial ryegrass, white clover, kikuyu grass and mixed pasture in the North Island of New Zealand. Myrothecium cinctum was particularly common on kikuyu grass, but otherwise plant species did not appear to affect their distribution. Numbers were greatest under warm conditions, in summer and autumn. No isolates were recovered from samples from the South Island. Cultures of most isolates of M. verrucaria, of some of M. roridum, of a few of M. leucotrichum and of none of M. cinctum, produced a cytotoxic reaction in tissue-culture cells of the type which was correlated with mammalian toxicity. Toxic isolates were most frequently recovered from irrigated pasture, but populations in the pastures examined were apparently too small to cause disease in grazing animals.
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- Genetics And Molecular Biology
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Mapping of the Pneumococcus Chromosome. Linkage between the Genes Conferring Resistances to Erythromycin and Tetracycline and Its Implication to the Replication of the Chromosome
More LessSUMMARY: In the process of constructing a map of the pneumococcus chromosome by transformation, a search for linkage groups involving the markers ery-r2, str-r41, amiA-r1, opt-r2 and tet-A has been carried out. No linkage was found amongst the first four markers, but linkage was found between ery-r2 and tet-A. The discrepancy between these results and the previously reported linkage between the loci conferring resistance to erythromycin and streptomycin is discussed. The anomalous position of the ery-r2–tet-A linkage in relation to the chromosome map obtained by the density-shift method, and the implications to the mode of replication of the chromosome, are discussed. Two models are proposed for the replication of the pneumococcal chromosome.
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- Medical Microbiology
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Serological Comparison of Bovine T-mycoplasmas
More LessSUMMARY: Eight bovine T-mycoplasmas examined serologically by the metabolism inhibition test, growth inhibition on agar and by immunofluorescence showed considerable serological heterogeneity. None of the eight strains was serologically identical with any other, but three formed a group of similar organisms. No evidence was obtained for one particular serotype being confined to a specific anatomical site or being isolated typically from any particular pathological condition. Antisera to the bovine T-mycoplasmas were tested against eight serologically distinct human strains and a caprine, a simian and a canine T-mycoplasma. None of the non-bovine strains was identical to these bovine T-mycoplasmas.
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- Physiology And Growth
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The Adsorption of Silver-labelled Fungal Pigment by Bacterial and Apple Plant Ribosomes
More LessSUMMARY: Extracellular material produced by Venturia inaequalis (the apple scab disease organism) formed a tightly bound complex with silver. The silver complex (in aqueous solution) was taken up by whole detached apple leaves (cultivar MM 109) and was observed in the petiole cytoplasm as ribosome-like particles. Diffuse deposits of silver were observed in the cell walls.
The silver complex was also taken up by a proportion of the particles present in ribosome preparations made from apple-leaf tissues and from bacterial cultures. Such complexed ribosomes were apparently swollen by internal adsorption of the substance, some showing (in the electron microscope) a faint halo round the central core; the cleft between the sub-units was visible. Comparatively few ribosomes from Pseudomonas mors-prunorum showed strong affinity for the silver complex. The ribosomal particles were similar in most respects to the particles seen in treated leaf petioles. Silver-complexed particles prepared from isolated ribosomes were degraded by ‘Pronase’ to ragged skeletal remnants which were further digested by pancreatic ribonuclease. The latter enzyme did not attack intact particles.
The results support evidence from earlier work that the progress of the disease is partly controlled by the effects of fungal pigments on host solute transport (possibly mediated via the cell-wall membrane system) and on hormone-controlled plant metabolism and photosynthesis (via the protein-synthesizing system).
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Control of Nitrogenase Synthesis in Klebsiella pneumoniae
More LessSUMMARY: Sulphate-limited continuous cultures of Klebsiella pneumoniae showed a proportional repression of nitrogenase activity with increasing concentrations of ammonium ion in the influent medium. A fully repressed population had a 50 % greater bacterial density than a fully derepressed one. On derepression, synthesis of nitrogenase lagged for 90 min after exhaustion of NH4 + from the medium but was complete within one doubling time. Casamino acids did not decrease the pre-fixation lag obtained under sulphate-limited conditions in the chemostat. Longer lags were obtained when NH4 + was exhausted under N-limited conditions. Such lags were decreased by Casamino acids, yeast extract, or l-aspartate. Aspartate-N completely repressed nitrogenase under sulphate- or carbon-limited conditions but not under nitrogen limitation. In the initial stages of repression of nitrogenase synthesis by NH4 +, apparent production of active enzyme continued for a short time in the absence of protein synthesis de novo; nitrogenase was then diluted out as the organisms multiplied. Repression by NH4 + was at the level of mRNA transcription according to studies with rifampicin and chloramphenicol. ‘Coding capacity’ for nitrogenase synthesis declined with a half-life of about 4.5 min following inhibition of RNA synthesis with rifampicin. NH4 + did not influence the decay rate but stimulated translation of such nitrogenase-specifying mRNA as had been initiated.
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- Short Communications
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Preparation of Sphaeroplasts from Lactobacillus casei by Growth with Low Concentration of Benzylpenicillin
More LessA strain of Lactobacillus casei used for the production of a lactic acid beverage is susceptible to phage infections. Calcium ions were required for the formation of PL-i phage-infected bacteria (Watanabe & Takesue, 1972). Further studies on the role of calcium ions in phage infection required the use of protoplasts or sphaeroplasts of the host bacteria. Early trials using egg-white lysozyme, EDTA or glycine to form sphaeroplasts were unsuccessful. However, a simple procedure to produce sphaeroplasts using a low concentration of benzylpenicillin has been successfully developed and is described here together with information on some factors affecting the stability of the sphaeroplasts.
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Production of Bacteriophage by Lyophilized and Oxygen-exposed Escherichia coli
E. Israeli and A. ShapiraLyophilized bacteria lose their ability to form colonies on nutrient media upon exposure to air (Naylor & Smith, 1946; Lion & Bergmann, 1961), oxygen being the lethal factor (Lion & Bergmann, 1961; Lion, 1963). The ability to reproduce decreases with exposure time. The ‘death’ of freeze-dried bacteria exposed to oxygen (FDO bacteria) does not abolish their ability to synthesize DNA, RNA and protein (Novick, Israeli & Kohn, 1972). However, DNA synthesis ceases a short time after reconstitution and β-galactosidase production is blocked, to be resumed only after a repair period.
In order to check whether protein and DNA synthetic mechanisms could function correctly under some other control than that of the cell, we investigated the ability of FDO bacteria to produce phage.
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