scholarly journals Functional analysis of the phospholipase C gene CaPLC1 and two unusual phospholipase C genes, CaPLC2 and CaPLC3, of Candida albicans

Microbiology ◽  
2005 ◽  
Vol 151 (10) ◽  
pp. 3381-3394 ◽  
Author(s):  
Donika Kunze ◽  
Inga Melzer ◽  
Désirée Bennett ◽  
Dominique Sanglard ◽  
Donna MacCallum ◽  
...  
Keyword(s):  
Candida Albicans ◽  
Phospholipase C ◽  
Essential Gene ◽  
Pathogenic Fungus ◽  
Systemic Infection ◽  
Cellular Processes ◽  
Solid Media ◽  
Transcriptional Pattern ◽  
Human Pathogenic Fungus ◽  
Hyphal Formation

Phospholipases C are known to be important regulators of cellular processes but may also act as virulence factors of pathogenic microbes. At least three genes in the genome of the human-pathogenic fungus Candida albicans encode phospholipases with conserved phospholipase C (Plc) motifs. None of the deduced protein sequences contain N-terminal signal peptides, suggesting that these phospholipases are not secreted. In contrast to its orthologue in Sacharomyces cerevisiae, CaPLC1 seems to be an essential gene. However, a conditional mutant with reduced transcript levels of CaPLC1 had phenotypes similar to Plc1p-deficient mutants in S. cerevisiae, including reduced growth on media causing increased osmotic stress, on media with a non-glucose carbon source, or at elevated or lower temperatures, suggesting that CaPlc1p, like the Plc1p counterpart in S. cerevisiae, may be involved in multiple cellular processes. Furthermore, phenotypic screening of the heterozygous ΔCaplc1/CaPLC1 mutant showed additional defects in hyphal formation. The loss of CaPLC1 cannot be compensated by two additional PLC genes of C. albicans (CaPLC2 and CaPLC3) encoding two almost identical phospholipases C with no counterpart in S. cerevisiae but containing structural elements found in bacterial phospholipases C. Although the promoter sequences of CaPLC2 and CaPLC3 differed dramatically, the transcriptional pattern of both genes was similar. In contrast to CaPLC1, CaPLC2 and CaPLC3 are not essential. Although Caplc2/3 mutants had reduced abilities to produce hyphae on solid media, these mutants were as virulent as the wild-type in a model of systemic infection. These data suggest that C. albicans contains two different classes of phospholipases C which are involved in cellular processes but which have no specific functions in pathogenicity.

scholarly journals Expression Patterns in Reductive Iron Assimilation and Functional Consequences during Phagocytosis of Lichtheimia corymbifera, an Emerging Cause of Mucormycosis

2021 ◽  
Vol 7 (4) ◽  
pp. 272
Author(s):  
Felicia Adelina Stanford ◽  
Nina Matthias ◽  
Zoltán Cseresnyés ◽  
Marc Thilo Figge ◽  
Mohamed I. Abdelwahab Hassan ◽  
...  
Keyword(s):  
Gene Expression ◽  
Iron Uptake ◽  
Intracellular Transport ◽  
Pathogenic Fungus ◽  
Expression Patterns ◽  
Iron Depletion ◽  
Iron Assimilation ◽  
Human Pathogenic Fungus ◽  
Hyphal Formation ◽  
Yeast Mutants

Iron is an essential micronutrient for most organisms and fungi are no exception. Iron uptake by fungi is facilitated by receptor-mediated internalization of siderophores, heme and reductive iron assimilation (RIA). The RIA employs three protein groups: (i) the ferric reductases (Fre5 proteins), (ii) the multicopper ferroxidases (Fet3) and (iii) the high-affinity iron permeases (Ftr1). Phenotyping under different iron concentrations revealed detrimental effects on spore swelling and hyphal formation under iron depletion, but yeast-like morphology under iron excess. Since access to iron is limited during pathogenesis, pathogens are placed under stress due to nutrient limitations. To combat this, gene duplication and differential gene expression of key iron uptake genes are utilized to acquire iron against the deleterious effects of iron depletion. In the genome of the human pathogenic fungus L. corymbifera, three, four and three copies were identified for FRE5, FTR1 and FET3 genes, respectively. As in other fungi, FET3 and FTR1 are syntenic and co-expressed in L. corymbifera. Expression of FRE5, FTR1 and FET3 genes is highly up-regulated during iron limitation (Fe-), but lower during iron excess (Fe+). Fe- dependent upregulation of gene expression takes place in LcFRE5 II and III, LcFTR1 I and II, as well as LcFET3 I and II suggesting a functional role in pathogenesis. The syntenic LcFTR1 I–LcFET3 I gene pair is co-expressed during germination, whereas LcFTR1 II- LcFET3 II is co-expressed during hyphal proliferation. LcFTR1 I, II and IV were overexpressed in Saccharomyces cerevisiae to represent high and moderate expression of intracellular transport of Fe3+, respectively. Challenge of macrophages with the yeast mutants revealed no obvious role for LcFTR1 I, but possible functions of LcFTR1 II and IVs in recognition by macrophages. RIA expression pattern was used for a new model of interaction between L. corymbifera and macrophages.

scholarly journals Release from Quorum-Sensing Molecules Triggers Hyphal Formation during Candida albicans Resumption of Growth

2005 ◽  
Vol 4 (7) ◽  
pp. 1203-1210 ◽  
Author(s):  
Brice Enjalbert ◽  
Malcolm Whiteway
Keyword(s):  
Candida Albicans ◽  
Quorum Sensing ◽  
Culture Medium ◽  
Pathogenic Fungus ◽  
Hyphal Growth ◽  
Growth Environment ◽  
Expression Of Genes ◽  
Genes Encoding ◽  
Hyphal Formation ◽  
Cyclin Genes

ABSTRACT Candida albicans is a pathogenic fungus able to change morphology in response to variations in its growth environment. Simple inoculation of stationary cells into fresh medium at 37°C, without any other manipulations, appears to be a powerful but transient inducer of hyphal formation; this process also plays a significant role in classical serum induction of hyphal formation. The mechanism appears to involve the release of hyphal repression caused by quorum-sensing molecules in the growth medium of stationary-phase cells, and farnesol has a strong but incomplete role in this process. We used DNA microarray technology to study both the resumption of growth of Candida albicans cells and molecular regulation involving farnesol. Maintaining farnesol in the culture medium during the resumption of growth both delays and reduces the induction of hypha-related genes yet triggers expression of genes encoding drug efflux components. The persistence of farnesol also prevents the repression of histone genes during hyphal growth and affects the expression of putative or demonstrated morphogenesis-regulating cyclin genes, such as HGC1, CLN3, and PCL2. The results suggest a model explaining the triggering of hyphae in the host based on quorum-sensing molecules.

scholarly journals Morphogenesis, Adhesive Properties, and Antifungal Resistance Depend on the Pmt6 Protein Mannosyltransferase in the Fungal Pathogen Candida albicans

2000 ◽  
Vol 182 (11) ◽  
pp. 3063-3071 ◽  
Author(s):  
Claudia Timpel ◽  
Sigrid Zink ◽  
Sabine Strahl-Bolsinger ◽  
Klaus Schröppel ◽  
Joachim Ernst
Keyword(s):  
Candida Albicans ◽  
Fungal Pathogen ◽  
Systemic Infection ◽  
Iron Chelator ◽  
Secreted Proteins ◽  
Adhesive Properties ◽  
Cell Extracts ◽  
Hydroxyphenylacetic Acid ◽  
Hyphal Formation ◽  
Mutant Phenotypes

ABSTRACT Protein mannosyltransferases (Pmt proteins) initiate O glycosylation of secreted proteins in fungi. We have characterizedPMT6, which encodes the second Pmt protein of the fungal pathogen Candida albicans. The residues of Pmt6p are 21 and 42% identical to those of C. albicans Pmt1p and S. cerevisiae Pmt6p, respectively. Mutants lacking one or twoPMT6 alleles grow normally and contain normal Pmt enzymatic activities in cell extracts but show phenotypes including a partial block of hyphal formation (dimorphism) and a supersensitivity to hygromycin B. The morphogenetic defect can be suppressed by overproduction of known components of signaling pathways, including Cek1p, Cph1p, Tpk2p, and Efg1p, suggesting a specific Pmt6p target protein upstream of these components. Mutants lacking bothPMT1 and PMT6 are viable and showpmt1 mutant phenotypes and an additional sensitivity to the iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid). The lack of Pmt6p significantly reduces adherence to endothelial cells and overall virulence in a mouse model of systemic infection. The results suggest that Pmt6p regulates a more narrow subclass of proteins in C. albicans than Pmt1p, including secreted proteins responsible for morphogenesis and antifungal sensitivities.

scholarly journals Defective Hyphal Development and Avirulence Caused by a Deletion of the SSK1 Response Regulator Gene in Candida albicans

2000 ◽  
Vol 68 (2) ◽  
pp. 518-525 ◽  
Author(s):  
José Antonio Calera ◽  
Xiao-Jiong Zhao ◽  
Richard Calderone
Keyword(s):  
Candida Albicans ◽  
Nitrogen Availability ◽  
Response Regulator ◽  
Hyphal Development ◽  
Isolation And Characterization ◽  
Solid Media ◽  
Functional Homolog ◽  
Good Target ◽  
Two Component ◽  
Hyphal Formation

ABSTRACT In a previous study, we reported the isolation and characterization of the two-component response regulator SSK1 gene ofCandida albicans. This gene is a structural but not a functional homolog of the SSK1 andmcs4 + genes of Saccharomyces cerevisiae and Schizosaccharomyces pombe, respectively. In the present study, we have constructed and phenotypically characterized Δssk1 mutants of C. albicans. The results confirmed our previous observation thatCaSSK1, unlike SSK1 ormcs4 +, does not regulate cellular responses to either osmotic or oxidative stress. Instead, Δssk1 null strains showed severely reduced hyphal formation on serum agar and were totally defective in hyphal development on other solid media, such as medium 199 (pH 7.5) and Spider medium. In contrast, under conditions of low nitrogen availability on solid media, Δssk1 null strains dramatically hyperinvaded the agar. However, while forming germ tubes and hyphae in liquid media similar to those of the wild type, Δssk1 null strains flocculated in a manner similar to that of Δchk1 two-component histidine kinase mutants, which we have previously described. Finally, virulence studies indicated that SSK1 is essential for the pathogenesis ofC. albicans, suggesting that the Ssk1p response regulator could be a good target for antifungal therapy.

scholarly journals A steep phosphoinositide bis-phosphate gradient forms during fungal filamentous growth

2012 ◽  
Vol 198 (4) ◽  
pp. 711-730 ◽  
Author(s):  
Aurélia Vernay ◽  
Sébastien Schaub ◽  
Isabelle Guillas ◽  
Martine Bassilana ◽  
Robert A. Arkowitz
Keyword(s):  
Long Range ◽  
Membrane Lipids ◽  
Pathogenic Fungus ◽  
Filamentous Growth ◽  
Asymmetric Distribution ◽  
Cell Morphogenesis ◽  
Membrane Diffusion ◽  
Cellular Processes ◽  
Human Pathogenic Fungus

Membrane lipids have been implicated in many critical cellular processes, yet little is known about the role of asymmetric lipid distribution in cell morphogenesis. The phosphoinositide bis-phosphate PI(4,5)P2 is essential for polarized growth in a range of organisms. Although an asymmetric distribution of this phospholipid has been observed in some cells, long-range gradients of PI(4,5)P2 have not been observed. Here, we show that in the human pathogenic fungus Candida albicans a steep, long-range gradient of PI(4,5)P2 occurs concomitant with emergence of the hyphal filament. Both sufficient PI(4)P synthesis and the actin cytoskeleton are necessary for this steep PI(4,5)P2 gradient. In contrast, neither microtubules nor asymmetrically localized mRNAs are critical. Our results indicate that a gradient of PI(4,5)P2, crucial for filamentous growth, is generated and maintained by the filament tip–localized PI(4)P-5-kinase Mss4 and clearing of this lipid at the back of the cell. Furthermore, we propose that slow membrane diffusion of PI(4,5)P2 contributes to the maintenance of such a gradient.

scholarly journals Niche-Specific Activation of the Oxidative Stress Response by the Pathogenic Fungus Candida albicans

2007 ◽  
Vol 75 (5) ◽  
pp. 2143-2151 ◽  
Author(s):  
Brice Enjalbert ◽  
Donna M. MacCallum ◽  
Frank C. Odds ◽  
Alistair J. P. Brown
Keyword(s):  
Oxidative Stress ◽  
Candida Albicans ◽  
Stress Response ◽  
Fluorescent Protein ◽  
Ex Vivo ◽  
Pathogenic Fungus ◽  
Systemic Infection ◽  
Oxidative Stress Response ◽  
Mammalian Host ◽  
Phagocytic Cells

ABSTRACT Candida albicans is a major opportunistic pathogen of humans. The pathogenicity of this fungus depends upon its ability to deal effectively with the host defenses and, in particular, the oxidative burst of phagocytic cells. We have explored the activation of the oxidative stress response in C. albicans in ex vivo infection models and during systemic infection of a mammalian host. We have generated C. albicans strains that contain specific green fluorescent protein (GFP) promoter fusions and hence act as biosensors of environmental oxidative stress at the single-cell level. Having confirmed that CTA1-, TRX1-, and TTR1/GRX2-GFP reporters respond specifically to oxidative stress, and not to heat shock, nitrosative, or osmotic stresses, we used these reporters to show that individual C. albicans cells activate an oxidative stress response following phagocytosis by neutrophils, but not by macrophages. Significantly, only a small proportion of C. albicans cells (about 4%) activated an oxidative stress response during systemic infection of the mouse kidney. The response of these cells was generally equivalent to exposure to 0.4 mM hydrogen peroxide in vitro. We conclude that most C. albicans cells are exposed to an oxidative stress when they come into contact with neutrophils in the bloodstream of the host but that oxidative killing is no longer a significant threat once an infection has been established in the kidney.

scholarly journals Hgc1 Mediates Dynamic Candida albicans-Endothelium Adhesion Events during Circulation

2009 ◽  
Vol 9 (2) ◽  
pp. 278-287 ◽  
Author(s):  
Duncan Wilson ◽  
Bernhard Hube
Keyword(s):  
Blood Pressure ◽  
Endothelial Cells ◽  
Candida Albicans ◽  
Pathogenic Fungus ◽  
Interaction Model ◽  
Serum Factors ◽  
Content Type ◽  
Disseminated Candidiasis ◽  
Human Pathogenic Fungus

ABSTRACT Common iatrogenic procedures can result in translocation of the human pathogenic fungus Candida albicans from mucosal surfaces to the bloodstream. Subsequent disseminated candidiasis and infection of deep-seated organs may occur if the fungus is not eliminated by blood cells. In these cases, fungal cells adhere to the endothelial cells of blood vessels, penetrate through endothelial layers, and invade deeper tissue. In this scenario, endothelial adhesion events must occur during circulation under conditions of physiological blood pressure. To investigate the fungal and host factors which contribute to this essential step of disseminated candidiasis, we have developed an in vitro circulatory C. albicans-endothelium interaction model. We demonstrate that both C. albicans yeast and hyphae can adhere under flow at a pressure similar to capillary blood pressure. Serum factors significantly enhanced the adhesion potential of viable but not killed C. albicans cells to endothelial cells. During circulation, C. albicans cells produced hyphae and the adhesion potential first increased, then decreased with time. We provide evidence that a specific temporal event in the yeast-to-hyphal transition, regulated by the G1 cyclin Hgc1, is critical for C. albicans-endothelium adhesion during circulation.

scholarly journals MNN5 Encodes an Iron-Regulated α-1,2-Mannosyltransferase Important for Protein Glycosylation, Cell Wall Integrity, Morphogenesis, and Virulence in Candida albicans

2006 ◽  
Vol 5 (2) ◽  
pp. 238-247 ◽  
Author(s):  
Chen Bai ◽  
Xiao-Li Xu ◽  
Fong-Yee Chan ◽  
Raymond Teck Ho Lee ◽  
Yue Wang
Keyword(s):  
Cell Wall ◽  
Candida Albicans ◽  
Iron Homeostasis ◽  
Pathogenic Fungus ◽  
Hyphal Growth ◽  
Protein Glycosylation ◽  
Host Cells ◽  
Microbial Pathogens ◽  
Solid Media ◽  
Wide Range

ABSTRACT The cell walls of microbial pathogens mediate physical interactions with host cells and hence play a key role in infection. Mannosyltransferases have been shown to determine the cell wall properties and virulence of the pathogenic fungus Candida albicans. We previously identified a C. albicans α-1,2-mannosyltransferase, Mnn5, for its novel ability to enhance iron usage in Saccharomyces cerevisiae. Here we have studied the enzymatic properties of purified Mnn5 and characterized its function in its natural host. Mnn5 catalyzes the transfer of mannose to both α-1,2- and α-1,6-mannobiose, and this activity requires Mn2+ as a cofactor and is regulated by the Fe2+ concentration. An mnn5Δ mutant showed a lowered ability to extend O-linked, and possibly also N-linked, mannans, hypersensitivity to cell wall-damaging agents, and a reduction of cell wall mannosylphosphate content, phenotypes typical of many fungal mannosyltransferase mutants. The mnn5Δ mutant also exhibited some unique defects, such as impaired hyphal growth on solid media and attenuated virulence in mice. An unanticipated phenotype was the mnn5Δ mutant's resistance to killing by the iron-chelating protein lactoferrin, rendering it the first protein found that mediates lactoferrin killing of C. albicans. In summary, MNN5 deletion impairs a wide range of cellular events, most likely due to its broad substrate specificity. Of particular interest was the observed role of iron in regulating the enzymatic activity, suggesting an underlying relationship between Mnn5 activity and cellular iron homeostasis.

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