- Volume 119, Issue 1, 1980
Volume 119, Issue 1, 1980
- Medical Microbiology
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Mode of Action of Miconazole on Candida albicans: Effect on Growth, Viability and K+ Release
More LessMiconazole at 10 g ml−1 inhibited the growth of exponential phase cultures of Candida albicans and released intracellular K+. Higher concentrations of miconazole were, however, required to cause cell death: at neutral pH, complete killing occurred at 30 g ml−1, while at pH 30 or 45, there was only partial killing with miconazole up to 80 g ml−1. Efficient killing of C. albicans by miconazole occurred both at low temperature and when cells were incubated in buffer alone. It is proposed that both the fungistatic and fungicidal actions of miconazole are due to its direct interaction with the cellular membranes of C. albicans rather than to an inhibition of biochemical reactions. Divalent cations protected C. albicans from both the fungistatic and fungicidal effects of miconazole and this was probably due to a competition between the ions and miconazole in its positively charged form for negatively charged binding sites. Candida albicans increased in resistance to miconazole-induced K+ release during the stationary phase of a batch culture. Development of this resistance required efficient aeration.
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- Physiology And Growth
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Carbon Metabolism in Microcystis under Low Light Intensities
More LessThe rate of total 14CO2 incorporation in the bloom-forming cyanobacterium Microcystis varied with light intensity, being minimal at 10 lux and increasing at both higher and lower intensities. The total labelling of compounds arising from phosphoenolpyruvate carboxylation (aspartate, glutamate and citrate) showed a minimum just below the light compensation point. At lower light intensities a marked increase in the percentage labelling of these compounds from 14CO2 occurred, together with a decrease in that of sugar phosphates and phosphoglycerate. The operation of the reductive pentose phosphate pathway was retarded at low light intensities; with increasing intensities the synthesis of sugars was favoured in relation to that of amino acids. This regulation of the route of CO2 fixation is discussed in relation to the survival of cyanobacteria under unfavourable environmental conditions.
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Why a Co-substrate is Required for Anaerobic Growth of Escherichia coli on Citrate
More LessCitrate was fermented by Escherichia coli if a second substrate, such as glucose, lactose or lactate, was available to the organism. The function of the second substrate was to provide reducing power for the formation of succinate from oxaloacetate. Citrate lyase, malate dehydrogenase, fumarase and fumarate reductase were present in cell extracts of E. coli at high activity. Oxaloacetate decarboxylase could not be detected, and it is assumed that this lack is the reason for the inability of E. coli to grow anaerobically with citrate as the only carbon and energy source.
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Bioenergetic Properties of Alkaline-tolerant and Alkalophilic Strains of Bacillus firmus
More LessThe protonmotive force, Na+/H+ antiport activity and a-aminoisobutyric acid transport were studied in alkaline-tolerant Bacillus firmus ATCC 14575 and in a newly isolated alkalophilic strain of the same species. The alkalophilic strain, which grew over a pH range from 8·0 to 10·5, maintained a cytoplasmic pH of 9·5 or below even at an external pH of 110. Evidence was obtained for an electrogenic Na+/H+ antiporter which could play a role in acidification of the cytoplasm as well as in generation of the transmembrane electrical potential. A non-alkalophilic strain, isolated after mutagenesis of the new alkalophile, lacked the Na+/H+ antiporter. The alkaline-tolerant strain of B. firmus, which grew at pH values between 6·5 and 8·5, did not maintain an acidified cytoplasm as the pH was raised above 8·0. A less active, apparently electroneutral, Na+/H+ exchange was found in this strain. Both the alkaline-tolerant and alkalophilic strains exhibited Na+-dependent transport of α-aminoisobutyric acid.
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Protection of Cell Viability and Respiratory Quinone Levels by Carotenoid in Micrococcus lysodeikticus (M. luteus)
More LessViability and respiratory activity of post-exponential phase cultures of Micrococcus lysodeikticus (M. luteus) decreased with time more rapidly in carotenoidless mutants than in a parent pigmented strain. The concentration of menaquinone, the respiratory quinone, was found to be low in carotenoidless mutants and in cultures of the pigmented strain where carotenoid synthesis had been partially blocked by diphenylamine. Cell suspensions incorporated [2-14C]mevalonate into menaquinone. Carotenoidless strains incorporated label at substantially higher rates than did the pigmented wild-type strain. Gently prepared membranes of M. lysodeikticus also incorporated mevalonate into menaquinone suggesting that the enzymes for the isoprenoid pathway are bound (loosely) to the membrane. Carotenoidless membranes with low concentrations of menaquinone incorporated radioactivity from [2-14C]mevalonate into quinone more rapidly than did membranes from the wild-type. Azide inhibited the incorporation but n-heptyl-4-hydroxyquinoline-N-oxide did not.
It is concluded that the low concentrations of menaquinone in carotenoidless strains are due to rapid breakdown of the quinone. Carotenoid is therefore seen as protecting menaquinone from breakdown by factors as yet unidentified.
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Separation on Urografin Gradients of Subpopulations from Sporulating Saccharomyces cerevisiae Cultures
More LessSporulating yeast populations were separated into a number of fractions by centrifugation through linear density gradients of Urografin. At least eight distinct fractions could be obtained from cultures that were just beginning to produce asci visible by phase contrast microscopy. Cells in these fractions were found to differ in the stage they had reached in meiosis and sporulation; those more advanced in sporulation banded at a lower density. Using this gradient centrifugation method it was shown that cultures induced to sporulate by the usual technique were markedly heterogeneous with respect to the stage in meiosis and sporulation reached by the cells, and that most of the labelled amino acids incorporated into protein by sporulating cultures appeared in those cells not yet committed to either recombination or meiosis.
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Effect of Tween 80 on the Morphology and Physiology of Lactobacillus salivarius Strain IV CL-37 Grown in a Chemostat under Glucose Limitation
More LessThe effect of Tween 80 on Lactobacillus salivarius strain IV CL-37 growing in a chemostat under various conditions was investigated. The organisms could grow under glucose limitation in the absence of Tween 80 at pH 6·0 or lower anaerobically but not aerobically. Aerobic growth under glucose limitation and in the presence of Tween 80 occurred in complete MRS medium but not in the dialysable fraction of MRS medium. The morphology of cells differed from coccal to filamentous and branched structures according to the growth condition. The possible effect of Tween 80 on membrane components was examined by estimating the cellular and extracellular lipoteichoic acid contents. In both batch and continuous culture the amounts of cellular lipoteichoic acid were inversely related to the amount of Tween 80 whereas the amounts of extracellular lipoteichoic acid were influenced by other factors in addition to Tween 80.
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The Reduction of Nitrate to Ammonium by a Clostridium sp. Isolated from Soil
More LessCultures of Clostridium KDHS2 reduced 15NO3 − to 15NH4 + with a concurrent increase in molar growth yield of 157% compared with fermentatively grown bacteria. The bacteria exhibited a K 8 (NO3 −) of 0·5 mm and reduced NO3-maximally at a rate of 01 mol h−1 (mg dry wt)−1. A partially purified nitrate reductase was obtained whichhad a K m (NO3-) of 0·15 mm. The reduction of 13NO3 − to 13NH4 + by resting bacteria was not inhibited by NH4 +, glutamate, glutamine, methionine sulphoximine or azaserine. Glutamine synthetase affected neither the synthesis nor the activity of the NO3 −-reducing enzymes. The results are consistent with the hypothesis that NO3 − reduction to NH4 + in this Clostridium sp. is dissimilative. SO3 2−, but not SO4 2−, inhibited the reaction, apparently at the level of NO2 − reduction.
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- Short Communication
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The Porosity of the Cell Wall of Candida albicans
More LessPolyethylene glycols of different molecular sizes have been used to study the penetrability of the cell wall of Candida albicans harvested at the end of the growth phase and after prolonged incubation in the stationary phase. No differences were found which could account for the greater resistance of cells from stationary phase cultures of C. albicans to the antimycotic agents amphotericin B methyl ester and miconazole.
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Expression of the Lactose Transposon Tn951 in Escherichia coli, Proteus and Pseudomonas
More LessThe control of β-galactosidase specified by the lactose transposon Tn951 (inserted into RP1 to give pGC9114) has been studied in Escherichia coli K12, Proteus mirabilis, Pseudomonas aeruginosa and Pseudomonas putida; in the first two species comparison could be made with Flac. In E. coli K12, the Tn951 and chromosomally encoded enzymes showed marked qualitative differences in regulation, the former giving a substantially lower maximum induced level and induction ratio. Several parameters were slightly affected by strain background. In P. mirabilis, β-galactosidase control determined by both Flac (in accord with earlier work) and pGC9114 was markedly different from E. coli in that maximal induced levels were about an order of magnitude lower and the induction ratio was reduced to 3 to 5. In Ps. aeruginosa and Ps. putida, Tn951-specified lac expression was qualitatively similar to that in P. mirabilis. Possible reasons for anomalous expression in Proteus and Pseudomonas are discussed.
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Thymidine Kinase Activity in Dictyostelium discoideum
More LessThymidine kinase activity is present in soluble and mitochondrial fractions of axenically grown cells of Dictyostelium discoideum. The overall activity does not change significantly during development.
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Succinate Uptake by Free-living and Bacteroid Forms of Rhizobium leguminosarum
More LessFree-living cells of Rhizobium leguminosarum possess a constitutive succinate uptake system. Bacteroids isolated from nodules of Pisum sativum also showed immediate uptake of succinate. In both cases the uptake of [14C] succinate appeared to be dependent on an energized membrane. Fumarate, malate and several succinate analogues were also transported via the succinate system. One or both of the carboxyl groups of the succinate molecule must be free in order to be recognized by the carrier. Glucose had effects on the uptake or metabolism of succinate.
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Isolation of Original Amino Acid, Vitamin and Carbon Source Mutants in the Green Alga Scenedesmus obliquus
More LessScenedesmus obliquus, grown under culture conditions which led to unicell populations, was treated with N-methyl-N′-nitro-N-nitrosoguanidine and then cells were plated on rich medium to recover auxotrophic mutants. Carbon source and vitamin (p-aminobenzoic acid, thiamin and nicotinamide)-requiring mutants were characterized. Amino acid-requiring mutants, some of types not previously isolated from green eukaryotes, were also obtained: 11 had a requirement for arginine, one for valine, two for threonine or isoleucine, and one for tryptophan, tyrosine or phenylalanine. The possible metabolic blocks of these amino acid-requiring mutants are discussed.
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Sensitivity of Synchronous Cultures of Bacillus subtilis to Lysozyme
More LessRates of lysis by lysozyme (expressed as the decrease in A 550 min−1) of synchronously dividing cells of Bacillus subtilis rose in concert with the stepwise increase in cell numbers. Asynchronously growing cells showed no periodicities in sensitivity; rates of lysis reflected the exponential increase in culture density.
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The Effects of Carbon Dioxide on Nitrogenase-related Activities of Rhodopseudomonas capsulata
More LessN2 fixation was investigated in suspensions of washed cells of the photosynthetic bacterium Rhodopseudomonas capsulata grown on various carbon and nitrogen sources. Maximum nitrogenase activities were common to cultures supplied with glutamate. Cells grown with nitrate contained appreciable nitrogenase activity and produced H2 in the light. Nitrogenase activity in washed cells derived from various nutritional conditions was markedly increased when NaHCO3 was included in the reaction mixtures.
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- Taxonomy
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The Taxonomic Implications of the Reactions of Representative Nocardia Strains to Actinophage
More LessThe sensitivity of representative Nocardia strains to phage isolated from species of this and other actinomycete genera was studied. Activity spectra of phage were closely correlated with the wall chemotypes of the test strains. The limits of the genus Nocardia sensu stricto as defined by phage sensitivity corresponded closely to those indicated by chemical and numerical taxonomy. The value of using phage sensitivity as an aid to the definition of actinomycete genera is emphasized.
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An Investigation of the Relationship between Bacillus cereus, Bacillus thuringiensis and Bacillus mycoides using Pyrolysis GasLiquid Chromatography
More LessNine strains of Bacillus mycoides, 10 of Bacillus cereus and 18 of Bacillus thuringiensis were analysed using pyrolysis gasliquid chromatography. Application of canonical variates analysis to the resultant pyrograms showed that these organisms formed three distinct groups. Stepwise discriminant analysis with jacknifing showed that of the original 27 peak heights used to define the canonical variates axes, only two were needed to obtain reasonably stable discriminant functions. These discriminant functions ( Dixon, 1975 ) are potentially valuable in identification. Jacknifing also indicated that, had it been an unknown, one strain of B. mycoides would have been incorrectly identified as B. cereus.
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Identification of the Group G Antigen of Lactobacilli
More LessThe group G antigen of lactobacilli was identified as a negatively-charged cell wall polysaccharide. The components of the preparation isolated from cell walls of L. salivarius subsp. salivarius by mild acid hydrolysis were glucose, galactose and lesser amounts of rhamnose, N-acetylglucosamine and phosphate. Quantitative serological studies on acid-released polysaccharide and enzymic lysates of cell walls showed that rhamnose was the immunodominant component. The antigen was also detected in L. salivarius subsp. salicinus but not in a recent isolate of L. salivarius, strain IV CL-37.
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- Addendum
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- Corrigendum
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Volumes and issues
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