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  • 1
    ISSN: 1432-072X
    Keywords: Candida albicans ; Dimorphism ; Internal pH ; Cell differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Non-dimorphic variants of Candida albicans, which were unable to form germ tubes or mature hyphae in media containing amino acids, glucose and salts or N-acetylglucosamine or serum, were prepared from two hyphal positive laboratory strains using a physical separation method. The hyphal-minus phenotype was stable and may be due to mutations or phenotypic variation. The variant strains maintained their internal pH within narrower bounds as compared to their parental wild-types. When exposed to conditions that normally supported the induction of germ tubes the cytoplasmic pH of the wild type strains increased from 6.8 to over pH 8.0 within 5 min while in the variants the rise in internal pH was only about 0.3 pH units. The wild type strains acidified the growth medium more rapidly than the variants. The results suggest that the control of internal pH is directly or indirectly associated with the regulation of dimorphism. The variants had unaltered cell volumes and specific growth rates. The hyphal-minus phenotype was however fully reversible since revertants occurred spontaneously on serum containing agar.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 75 (1989), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The electrical currents associated with developing primary root tips of Triticum aestivum L. cv. Slejpner, Avena sativa L. cv. Victory I, Lolium perenne L. cv. Melle, Vigna radiata (L.) Wilczek, Arachis hypogaea L., Pisum sativum L. cv. Keluedon Wonder, Lonchocarpus leucanthus Burk, Dalbergia nigra Fr. Allen and Picea abies (L.) Karst. (U. K. Forestry Commission Number: 85/498/B). and that of the adventitious root tips of Fragaria vesca L., Solanum tuberosum L. cv. Maris Piper and Neptunia plena Lindl. were examined with a vibrating electrode. Current was found consistently to enter the meristematic and elongating tissues of all the intact growing roots examined. Mature non-growing root regions were responsible for generating the outword limb of the current loop. Peak inward current densities ranged between 2 mA m−2 (Lolium) and 28 mA m−2 (Arachis). The point at which the inward current reversed to outward current also varied between species. These results, which are derived from 5 taxonomically diverse families (Graminae, Leguminosae, Rosaceae, Solanaceae and Pinaceae) extend the range of different species that have been shown to generate ion currents that transverse, in a highly polar manner, the growing regions of their root systems. This supports the correlations between endogenous current generation and root development.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 81 (1991), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: The rates of germ tube formation from growing and non-growing yeast cells of Candida albicans were investigated using a protocol for dimorphism regulated by temperature and pH. Stationary-phase cells formed germ tubes less rapidly than yeast cells that were preincubated in fresh growth medium prior to induction of dimorphism by an upshift in temperature or pH. On the basis of experiments using inhibitors of macromolecular biosyntheses it is suggested that the accelerated growth kinetics required de novo RNA and protein biosynthesis, but not DNA synthesis. The results suggest that metabolically active yeast cells are better able to undergo dimorphism than non-growing cells.
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Chromosomal rearrangements are common in both clinical isolates and spontaneous mutants of Candida albicans. It appears that many of these rearrangements are caused by translocations around the major sequence repeat (MSR) that is present in all chromosomes except chromosome 3, suggesting that homologous recombination (HR) may play an important role in the survival of this organism. In order to gain information on these processes, we have cloned the homologue of RAD52, which in Saccharomyces cerevisiae is the only gene required for all HR events. CaRAD52 complemented poorly a rad52 mutant of S. cerevisiae. Two null Carad52Δ/Carad52Δ mutants were constructed by sequential deletion of both alleles and two reconstituted strains were obtained by reintegration of the gene. Characterization of these mutants indicated that HR plays an essential role in the repair of DNA lesions caused by both UV light and the radiomimetic compound methyl-methane-sulphonate (MMS), whereas the non-homologous end-joining pathway (NHEJ) is used only in the absence of Rad52p or after extensive DNA damage. Repair by HR is more efficient in exponentially growing than in stationary cells, probably because a larger number of cells are in late S or G2 phases of the cell cycle (and therefore, can use a sister chromatid as a substrate for recombinational repair), whereas stationary phase cells are mainly in G0 or G1, and only can be repaired using the chromosomal homologue. In addition, CaRad52p  is  absolutely  required  for  the  integration of linear DNA with long flanking homologous sequences. Finally, the absence of CaRad52p results in the lengthening of telomeres, even in the presence of an active telomerase, an observation not described in any other organism. This raises the possibility that both telomerase and homologous recombination may function simultaneously at C. albicans telomeres.
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Several microbial pathogens augment their invasive potential by binding and activating human plasminogen to generate the proteolytic enzyme plasmin. Yeast cells and cell wall proteins (CWP) of the human pathogenic fungus Candida albicans bound plasminogen with a Kd of 70 ± 11 nM and 112 ± 20 nM respectively. Bound plasminogen could be activated to plasmin by mammalian plasminogen activators; no C. albicans plasminogen activator was detected. Binding of plasminogen to CWP and whole cells was inhibited by ɛACA, indicating that binding was predominantly to lysine residues. Candida albicans mutant strains defective in protein glycosylation did not show altered plasminogen binding, suggesting that binding was not mediated via a surface lectin. Binding was sensitive to digestion by basic carboxypeptidase, implicating C-terminal lysine residues in binding. Proteomic analysis identified eight major plasminogen-binding proteins in isolated CWP. Five of these (phosphoglycerate mutase, alcohol dehydrogenase, thioredoxin peroxidase, catalase, transcription elongation factor) had C-terminal lysine residues and three (glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and fructose bisphosphate aldolase) did not. Activation of plasminogen could potentially increase the capacity of this pathogenic fungus for tissue invasion and necrosis. Although surface-bound plasmin(ogen) degraded fibrin, no direct evidence for a role in invasion of endothelial matrix or in penetration and damage of endothelial cells was found.
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  • 6
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Two genes, designated chsC and chsG were isolated from DNA libraries of the opportunistic fungal pathogen, Aspergillus fumigatus. The genes were characterized with respect to their nucleotide sequences and mutant phenotypes. The complete deduced amino acid sequences of chsC and chsG show that the products of both genes are Class III zymogen-type enzymes. A mutant strain constructed by disruption of chsC is phenotypically indistinguishable from the wild-type strain, but chsG− and chsC− chsG− strains have reduced colony radial growth rate and chitin synthase activity, conidiate poorly and produce highly branched hyphae. Despite these defects, the double-mutant strain retained the ability to cause pulmonary disease in neutropenic mice. However, in comparison to the wild-type strain, there was a decrease in mortality and delay in the onset of illness in mice inoculated with the double-mutant strain, which was associated with smaller and more highly branched fungal colonies in lung tissue.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 204 (2001), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gene disruptions in the diploid opportunistic human fungal pathogen Candida albicans are usually created using multiple rounds of targeted integration called the ‘ura-blaster’ method. Resulting heterozygous and homozygous null mutants can be auxotrophic (Ura−) or prototrophic (Ura+) for uracil biosynthesis. Here we demonstrate that the Ura-status of otherwise isogenic mutants affected the adhesion of C. albicans. Moreover the effect of Ura-status on adhesion was also dependent on the null mutant background, the nature of the underlying surface and the carbon source for growth. Therefore the Ura-status is not neutral in determining adhesive properties of C. albicans mutants that are generated via the ura-blaster protocol.
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  • 8
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Transgenic Phytophthora palmivora strains that produce green fluorescent protein (GFP) or β-glucuronidase (GUS) constitutively were obtained after stable DNA integration using a polyethylene-glycol and CaCl2-based transformation protocol. GFP and GUS production were monitored during several stages of the life cycle of P. palmivora to evaluate their use in molecular and physiological studies. 40% of the GFP transformants produced the GFP to a level detectable by a confocal laser scanning microscope, whereas 75% of the GUS transformants produced GUS. GFP could be visualised readily in swimming zoospores and other developmental stages of P. palmivora cells. For high magnification microscopic studies, GFP is better visualised and was superior to GUS. In contrast, for macroscopic examination, GUS was superior. Our findings indicate that both GFP and GUS can be used successfully as reporter genes in P. palmivora.
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: CaCHS1 of the fungal pathogen Candida albicans encodes an essential chitin synthase that is required for septum formation, viability, cell shape and integrity. The CaCHS1 gene was inactivated by first disrupting one allele using the ura-blaster protocol, then placing the remaining allele under the control of the maltose-inducible, glucose-repressible MRP1 promoter. Under repressing conditions, yeast cell growth continued temporarily, but daughter buds failed to detach from parents, resulting in septumless chains of cells with constrictions defining contiguous compartments. After several generations, a proportion of the distal compartments lysed. The conditional Δchs1 mutant also failed to form primary septa in hyphae; after several generations, growth stopped, and hyphae developed swollen balloon-like features or lysed at one of a number of sites including the hyphal apex and other locations that would not normally be associated with septum formation. CHS1 therefore synthesizes the septum of both yeast and hyphae and also maintains the integrity of the lateral cell wall. The conditional mutant was avirulent under repressing conditions in an experimental model of systemic infection. Because this gene is essential in vitro and in vivo and is not present in humans, it represents an attractive target for the development of antifungal compounds.
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