- Volume 138, Issue 4, 1992
Volume 138, Issue 4, 1992
- Physiology And Growth
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Selection and characterization of Aspergillus nidulans mutants involved in regulation of glycerol metabolism
More LessSummary: Pathway-specific induction plays an important role in Aspergillus nidulans when this fungus is grown on media containing glycerol as carbon source. To obtain mutants altered in regulation of glycerol metabolism, we used a glcB mutant strain, which is unable to grow on mixed carbon sources like d-glucose/glycerol as it accumulates G3P. Pseudorevertants, derived from this strain after mutagenesis as able to grow on d-glucose/glycerol, were analysed. In addition to glycerol kinase mutants and glycerol uptake mutants four new classes of mutants were found. Biochemical and genetic data indicate that the glcH mutants found are likely to lack a positive factor necessary for full induction of glycerol kinase and glycerol-3-phosphate dehydrogenase activities. The phenotype of a temperature-sensitive glcI mutant was found to be influenced by oxygen tension. Elevated levels of intracellular phosphatase were found in a glcL mutant. The glcK1 mutant had slow growth rates and higher levels of phosphofructokinase and fructose-6-phosphate reductase.
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Induction of bacterial luciferase by pure oxygen
More LessSummary: Xenorhabdus luminescens is a terrestrial bacterium that occurs as a symbiont of soil nematodes, and has also been isolated from human wounds. Unlike the several species of marine bioluminescent bacteria, X. luminescens has been discovered to grow in an atmosphere of 100% oxygen. Under these conditions the in vivo bioluminescence is greater, and this can be attributed in part to an increased synthesis of luciferase. At the same time, cells also produce superoxide dismutase (SOD), whose activity is also increased after growth in 100% oxygen. The patterns of induction suggest that the two enzymes are co-regulated; possible evolutionary relationships are considered.
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The gas permeability coefficient of the cyanobacterial gas vesicle wall
More LessSummary: The gas permeability coefficient of the cyanobacterial gas vesicle wall has been determined by comparing the concentration gradient of oxygen gas in a film of gas vesicles with the gradient in an underlying film of agar supported over an oxygen atmosphere. The gradients were determined with an oxygen microelectrode. The value of the gradient in aqueous agar was 0·81 of that in a suspension in which gas vesicles occupied 0·35 of the total volume. From this it was calculated that the notional diffusivity of oxygen through the gas vesicle was equivalent to 0·53 of the diffusivity in water. The permeability coefficient of the gas vesicle membrane is calculated to be k = 32 mm s −1, the rate coefficient for filling the gas vesicle by diffusion is a = 2·4 x 106 s −1 and the folding time for equilibration of gas into a gas vesicle is t e = 0·4 μs. The permeability coefficient is about 100-fold higher than the minimum value set by previous pressure rise experiments, and confirms that gas vesicles could not store gas. The measurements also show, however, that randomly oriented gas vesicles would not provide a diffusion channel with a diffusivity higher than that in water, although a layer of gas vesicles oriented with their long axes parallel to the diffusion gradient would provide a diffusivity 3·5-fold higher. The determination of the diffusivity was made with a theory, based on diffusion equations, which can be used in the determination of the diffusivity through other cell organelles.
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- Corrigendum
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