Metabolism Of Candida Albicans Research Articles

Glycogen Metabolism in Candida albicans Impacts Fitness and Virulence during Vulvovaginal and Invasive Candidiasis.

The polymorphic fungus Candida albicans remains a leading cause of both invasive and superficial mycoses, including vulvovaginal candidiasis (VVC). Metabolic plasticity, including carbohydrate catabolism, confers fitness advantages at anatomical site-specific host niches. C. albicans possesses the capacity to accumulate and store carbohydrates as glycogen and can consume intracellular glycogen stores when nutrients become limited. In the vaginal environment, estrogen promotes epithelial glycogen accumulation and C. albicans colonization. However, whether these factors are mechanistically linked is unexplored. Here, we characterized the glycogen metabolism pathways in C. albicans and investigated whether these impact the long-term survival of C. albicans, both in vitro and in vivo during murine VVC, or virulence during systemic infection. SC5314 and 6 clinical isolates demonstrated impaired growth when glycogen was used as the sole carbon source, suggesting that environmental glycogen acquisition is limited. The genetic deletion and complementation of key genes involved in glycogen metabolism in Saccharomyces cerevisiae confirmed that GSY1 and GLC3, as well as GPH1 and GDB1, are essential for glycogen synthesis and catabolism in C. albicans, respectively. Potential compensatory roles for a glucoamylase encoded by SGA1 were also explored. Competitive survival assays revealed that gsy1Δ/Δ, gph1Δ/Δ, and gph1Δ/Δ sga1Δ/Δ mutants exhibited long-term survival defects in vitro under starvation conditions and in vivo during vaginal colonization. A complete inability to catabolize glycogen (gph1Δ/Δ sga1Δ/Δ) also rendered C. albicans significantly less virulent during disseminated infections. This is the first study fully validating the glycogen metabolism pathways in C. albicans, and the results further suggest that intracellular glycogen catabolism positively impacts the long-term fitness of C. albicans in nutrient deficient environments and is important for full virulence. IMPORTANCE Glycogen is a highly branched polymer of glucose and is used across the tree of life as an efficient and compact form of energy storage. Whereas glycogen metabolism pathways have been studied in model yeasts, they have not been extensively explored in pathogenic fungi. Using a combination of microbiologic, molecular genetic, and biochemical approaches, we reveal orthologous functions of glycogen metabolism genes in the fungal pathogen Candida albicans. We also provide evidence that extracellular glycogen poorly supports growth across the Candida species and clinical isolates. Competitive fitness assays reveal that the loss of glycogen synthesis or catabolism significantly impacts survival during both in vitro starvation and the colonization of the mouse vagina. Moreover, a global glycogen catabolism mutant is rendered less virulent during murine invasive candidiasis. Therefore, this work demonstrates that glycogen metabolism in C. albicans contributes to survival and virulence in the mammalian host and may be a novel antifungal target.

Genetic and biochemical analysis of the reserve carbohydrate metabolism in Candida albicans and Candida rugosa

Genetic and biochemical analysis of the reserve carbohydrate metabolism in Candida albicans and Candida rugosa

Effects of fluconazole on the metabolomic profile of Candida albicans.

Little is known about the effects of fluconazole on the metabolism of Candida albicans. We performed LC/MS-based metabolomic profiling of the response of C. albicans cells to increasing doses of fluconazole. C. albicans cells were cultured to mid-logarithmic growth phase in liquid medium and then inoculated in replicate on to nitrocellulose filters under vacuum filtration. Organisms were cultured to mid-logarithmic growth phase and treated with 0-4 mg/L fluconazole. Following metabolic quenching at mid-logarithmic growth phase, intracellular metabolites were extracted and analysed by LC/MS. Changes in pool sizes of individual metabolites were verified by Student's t-test, adjusted for multiple hypothesis testing by Benjamini-Hochberg correction. Distribution of metabolites was analysed by the Kyoto Encyclopedia of Genes and Genomes metabolic pathways database. We reproducibly detected 64 metabolites whose identities were confirmed by comparison against a pure standard and a library of accurate mass-retention time pairs. These 64 metabolites were broadly representative of eukaryotic central metabolic pathways. Among them 12 had their mean abundance significantly altered in response to increasing fluconazole concentrations. Pool sizes of four intermediates of central carbon metabolism (α-ketoglutarate, glucose-6-phosphate, phenylpyruvate and ribose-5-phosphate) and mevalonate were increased by 0.5-1.5-fold (P ≤ 0.05). Five amino acids (glycine, proline, tryptophan, aminoisobutanoate and asparagine) and guanine were decreased by 0.5-0.75-fold (P ≤ 0.05). Fluconazole treatment of C. albicans resulted in increased central carbon and decreased amino acid synthesis intermediates, suggesting a rerouting of metabolic pathways. The function of these metabolomic changes remains to be elucidated; however, they may represent previously unrecognized mechanisms of metabolic injury induced by fluconazole against C. albicans.

Characterization of extracellular nucleotide metabolism in Candida albicans.

Candida albicans is the most frequent agent of human disseminated fungal infection. Ectophosphatase and ectonucleotidase activities are known to influence the infectious potential of several microbes, including other non-albicans species of Candida. With the present work we aim to characterize these ecto-enzymatic activities in C. albicans. We found that C. albicans does not have a classical ecto-5'-nucleotidase enzyme and 5'AMP is cleaved by a phosphatase instead of exclusively by a nucleotidase that also can use 3'AMP as a substrate. Moreover, these enzymatic activities are not dependent on secreted soluble enzymes and change when the yeast cells are under infection conditions, including low pH, and higher temperature and CO2 content.

The effect of thyme and tea tree oils on morphology and metabolism of Candida albicans.

Members of Candida species cause significant problems in medicine and in many industrial branches also. In order to prevent from Candida sp. development, essential oils are more and more frequently applied as natural, non-toxic, non-pollutive and biodegradable agents with a broad spectrum of antimicrobial activity. The aim of the research was to determine changes in morphology and metabolic properties of Candida albicans in the presence of thyme and tea tree oils. Changes of enzymatic activity of isolates were observed in the presence of both tested essential oils, and they were primarily associated with loss or decrease of activity of all enzymes detected for control. Furthermore, only for 3 out of 11 isolates additional activity of N-acetyl-β-glucosaminidase, α-mannosidase, α-fucosidase and trypsin was detected. Vivid changes in biochemical profiles were found after treatment with tea tree oil and they were related to loss of ability to assimilate D-xylose, D-sorbitol and D-trehalose. The main differences in morphology of isolates compared to the control strain concerned formation of pseudohyphae structures. Both examined essential oils caused changes in cell and colony morphology, as well as in the metabolism of Candida albicans. However, the extent of differences depends on the type and concentration of an essential oil. The most important finding is the broad spectrum of changes in yeast enzymatic profiles induced by thyme and tea tree oils. It can be supposed that these changes, together with loss of ability to assimilate saccharides could significantly impact Candida albicans pathogenicity.

Identification and functional characterization of mitochondrial carrier Mrs4 inCandida albicans

Iron is an essential nutrient required for the growth and metabolism in Candida albicans. Here, we for the first time identified Mrs4 as a new member of mitochondrial carrier family in C. albicans. Our experiments revealed that C. albicans Mrs4 (CaMrs4) is localized to the mitochondria and required for mitochondrial morphology. We found that CaMrs4 is required for cell growth, and the mrs4Δ/Δ mutant showed a more severe growth defect in iron deficiency. Deletion of MRS4 affected cellular iron content by altering the expression of iron regulon genes in C. albicans, such as AFT2, SMF3, FTR1 and ISU1. Candida albicans Aft2 factor functions as a negative regulator of MRS4 expression through the CACCC Aft-type sequence in a gene dose-dependent fashion. In addition, the mrs4Δ/Δ mutant exhibited hypersensitivity to oxidants and most metal ions, but decreased sensitivity to cobalt. Exogenous iron could suppress the sensitivity of the mrs4Δ/Δ mutant to oxidants and most metal ions, suggesting that the role of CaMrs4 is partially mediated by iron availability. Furthermore, deletion of MRS4 resulted in delayed filamentation under tested conditions. Taken together, these findings characterize a new mitochondrial carrier and provide a novel insight into the role of CaMrs4 in mitochondrial function.

Target specificity of the Candida albicans Efg1 regulator

Efg1 is a central transcriptional regulator of morphogenesis and metabolism in Candida albicans. In vivo genome-wide ChIP chip and in vitro footprint analyses revealed the Efg1 recognition sequence (EGR-box) TATGCATA in the yeast growth form of this human fungal pathogen. Upstream regions of EFG1 and genes encoding transcriptional regulators of hyphal growth including TCC1, CZF1, TEC1, DEF1 and NRG1 contained EGR- and/or EGR-like boxes. Unexpectedly, after brief hyphal induction the genome-wide Efg1 binding pattern was completely altered and new binding sites of yet unknown specificity had appeared. Hyphal induction abolished Efg1 accumulation on EFG1 and TCC1 promoters and led to rapid decline of both transcripts, although the Efg1 protein persisted in cells. While EFG1 promoter activity in the yeast growth form did not depend on bound Efg1, its downregulation under hyphal induction depended on the presence of Efg1 and the protein kinase A isoform Tpk2. Deletion analyses of the EFG1 upstream region revealed that none of its resident EGR-boxes is uniquely responsible for EFG1 promoter downregulation. These results suggest different binding specificities of Efg1 in yeast growth and in hyphal induction and suggest a brief time window following hyphal induction, in which Efg1 exerts its repressive effect on target promoters.

Tea polyphenol epigallocatechin-3-gallate inhibits ergosterol synthesis by disturbing folic acid metabolism in Candida albicans

Elucidation of the mechanism of action of epigallocatechin-3-gallate (EGCG) against Candida albicans and demonstration of the connection between its antifolate activity and other metabolic pathways involved in C. albicans survival are the major objectives of this study. C. albicans ATCC 10231 and 12 clinical isolates were used. MICs of EGCG against C. albicans were determined according to NCCLS. C. albicans dihydrofolate reductase (DHFR) was purified using methotrexate-affinity chromatography and its inhibition by EGCG studied by spectroscopic techniques. Synergy experiments were performed by chequerboard tests by combining eight doubling concentrations of EGCG with another eight dilutions of azole compounds or terbinafine. Reversion experiments with leucovorin or S-adenosylmethionine were carried out, and the content of ergosterol was determined by a spectrophotometric method. EGCG is an efficient inhibitor of C. albicans DHFR (K(i) = 0.7 microM). As with other antifolates, the effects of EGCG on C. albicans can be highly attenuated by growing the cells in the presence of leucovorin. EGCG showed synergy with inhibitors of the ergosterol biosynthesis pathway in C. albicans such as azole antifungals and terbinafine. We demonstrate that by disturbing the folate metabolism, EGCG can inhibit ergosterol production. The molecular connection between the pathways is discussed. EGCG acts as an antifolate compound on C. albicans, disturbing its folic acid metabolism. This effect could explain the molecular mechanism for the synergy between EGCG and azole antifungals, and could represent a starting point for therapies involving antifolates and azoles used as an alternative for the treatment of C. albicans infections.

Regulation of sterol metabolism in Candida albicans by the UPC2 gene

Candida albicans is an important pathogenic fungus of humans, causing a range of infections. These infections are usually treated with antifungal drugs that target sterol metabolism. Resistance to these antifungals can result from overexpression of sterol biosynthetic genes. Therefore it is of interest to understand transcriptional regulation of sterol biosynthesis in C. albicans. Recently two reports [Silver, Oliver and White (2004) Eukaryot. Cell 3, 1391-1397; MacPherson, Akache, Weber, De Deken, Raymond and Turcotte (2005) Antimicrob. Agents Chemother. 49, 1745-1752] have identified and characterized a single C. albicans transcription factor gene UPC2 that regulates sterol metabolism. The details of both characterizations are compared and contrasted. These reports extend our understanding of sterol regulation in this important human pathogen.

APSES Proteins Regulate Morphogenesis and Metabolism in Candida albicans

APSES Proteins Regulate Morphogenesis and Metabolism in Candida albicans

APSES proteins regulate morphogenesis and metabolism in Candida albicans.

Fungal APSES proteins regulate morphogenetic processes, including filamentation and differentiation. The human fungal pathogen Candida albicans contains two APSES proteins: the regulator Efg1p and its homologue Efh1p, described here. Overexpression of EFG1 or EFH1 led to similar phenotypes, including pseudohypha formation and opaque-white switching. An efh1 deletion generated no phenotype under most conditions but caused hyperfilamentation in an efg1 background under embedded or hypoxic conditions. This suggests cooperation of these APSES proteins in the suppression of an alternative morphogenetic signaling pathway. Genome-wide transcriptional profiling revealed that EFG1 and EFH1 regulate partially overlapping sets of genes associated with filament formation. Unexpectedly, Efg1p not only regulates genes involved in morphogenesis but also strongly influences the expression of metabolic genes, inducing glycolytic genes and repressing genes essential for oxidative metabolism. Using one- and two-hybrid assays, we further demonstrate that Efg1p is a repressor, whereas Efh1p is an activator of gene expression. Overall, the results suggest that Efh1p supports the regulatory functions of the primary regulator, Efg1p, and indicate a dual role for these APSES proteins in the regulation of fungal morphogenesis and metabolism.

Influence of W-7, a calmodulin antagonist on phospholipid biosynthesis in Candida albicans.

This study was undertaken to investigate the role of calmodulin in phospholipid biosynthesis in Candida albicans using W-7, a calmodulin antagonist. Cells were grown as shake cultures in the absence and presence of W-7 at different concentrations. Changes in cell mass, phospholipid content and incorporation of labelled precursor into phospholipid and activities of respective enzymes have been studied. Decreased incorporation of labelled acetate into total lipids and phospholipids was observed in the presence of 40 microm of W-7 which was not as a consequence of altered growth of Candida in the presence of calmodulin antagonist. Further, a significant decrease in the levels of calmodulin and CaM dependent protein kinase activity was observed in cells grown with different concentrations of W-7. This was accompanied by decreased/increased activity of phosphatidic acid phosphatase and phospholipase A, respectively in W-7 grown cells as compared to controls. These findings suggest definite involvement of calmodulin in the regulation of phospholipid metabolism in Candida albicans.

Influence of sub-inhibitory concentrations of conventional antifungals on metabolism of Candida albicans and on its adherence to polystyrene and extracellular matrix proteins

Influence of sub-inhibitory concentrations of conventional antifungals on metabolism of Candida albicans and on its adherence to polystyrene and extracellular matrix proteins

Glycine metabolism in Candida albicans: characterization of the serine hydroxymethyltransferase (SHM1, SHM2) and threonine aldolase (GLY1) genes.

Genes encoding the mitochondrial (SHM1) and cytosolic (SHM2) serine hydroxymethyltransferases, and the L-threonine aldolase gene (GLY1) from Candida albicans were cloned and sequenced. All three genes are involved in glycine metabolism. The C. albicans Shm1 protein is 82% identical to that from Saccharomyces cerevisiae and 56% identical to that from Homo sapiens. The corresponding identities for the Shm2 proteins are 68% and 53%. The Gly1 protein shares significant identity with the S. cerevisiae L-threonine aldolase (55%) and also with threonine aldolases from Aeromonas jandiae (36%) and Escherichia coli (36%). Genetic ablation experiments show that GLY1 is a non-essential gene in C. albicans and that L-threonine aldolase plays a lesser role in glycine metabolism than it does in S. cerevisiae. GenBank Accession Nos of the C. albicans SHM1 and SHM2 are AF009965 and AF009966, respectively. Accession No. for C. albicans GLY1 is AF009967.

D-arabitol metabolism in Candida albicans: construction and analysis of mutants lacking D-arabitol dehydrogenase.

Candida albicans produces large amounts of the acyclic pentitol D-arabitol in culture and in infected animals and humans, and most strains also grow on minimal D-arabitol medium. An earlier study showed that the major metabolic precursor of D-arabitol in C. albicans was D-ribulose-5-PO4 from the pentose pathway, that C. albicans contained an NAD-dependent D-arabitol dehydrogenase (ArDH), and that the ArDH structural gene (ARD) encoded a 31-kDa short-chain dehydrogenase that catalyzed the reaction D-arabitol + NAD <=> D-ribulose + NADH. In the present study, we disrupted both ARD chromosomal alleles in C. albicans and analyzed the resulting mutants. The ard null mutation was verified by Southern hybridization, and the null mutant's inability to produce ArDH was verified by Western immunoblotting. The ard null mutant grew well on minimal glucose medium, but it was unable to grow on minimal D-arabitol or D-arabinose medium. Thus, ArDH catalyzes the first step in D-arabitol utilization and a necessary intermediate step in D-arabinose utilization. Unexpectedly, the ard null mutant synthesized D-arabitol from glucose. Moreover, 13C nuclear magnetic resonance studies showed that the ard null mutant and its wild-type parent synthesized D-arabitol via the same pathway. These results imply that C. albicans synthesizes and utilizes D-arabitol via separate metabolic pathways, which was not previously suspected for fungi.

D-arabitol metabolism in Candida albicans: studies of the biosynthetic pathway and the gene that encodes NAD-dependent D-arabitol dehydrogenase

Candida albicans produces large amounts of the pentitol D-arabitol in culture and in infected mammalian hosts, but the functional and pathogenic significance of D-arabitol in C. albicans is not known. In this study, we sought to elucidate the pathway by which C. albicans synthesizes D-arabitol and to identify and characterize key enzymes in this pathway. C. albicans B311 produced D-[14C-1]arabitol from [14C-2]glucose; this finding implies on structural grounds that D-ribulose-5-PO4 from the pentose pathway is the major metabolic precursor of D-arabitol. NAD- or NADP-dependent pentitol dehydrogenases catalyze the final steps in D-arabitol biosynthesis in other fungi; therefore, lysates of C. albicans B311 were tested for enzymes of this class and were found to contain a previously unknown NAD-dependent D-arabitol dehydrogenase (ArDH). The ArDH structural gene was cloned by constructing a new D-arabitol utilization pathway in Escherichia coli. The C. albicans ArDH gene expressed in E. coli and Saccharomyces cerevisiae an enzyme that catalyzes the reaction D-arabitol + NAD <-->D-ribulose + NADH; this gene was present as a single copy per haploid genome, and its deduced peptide sequence was homologous with sequences of several members of the short-chain dehydrogenase family of enzymes. These results suggest that (i) C. albicans synthesizes D-arabitol by dephosphorylating and reducing the pentose pathway intermediate D-ribulose-5-PO4 and (ii) ArDH catalyzes the final step in this pathway.

Perturbation of growth and metabolism in Candida albicans by 4-bromobenzyl isothiocyanate and iodoacetate.

The inhibition by PBBI of growing Candida albicans was studied; additional information was obtained from the analysis of regeneration. The type of the growth inhibition depended on the cell suspension. At more than 107 cells per ml, the inhibition was transient; the inhibitor was taken up rapidly by the cells to a limit of 37 nmoles per mg dry wet. At higher doses, the growth was inhibited permanently, and then, and only then, a lethal effect was observed. At sublethal doses of the inhibitor, the following effects were observed: Inhibition of respiration without apprecciable .change in R.Q., of incorporation of labelled precursors into proteins and nucleic acids, and of eight of fourteen enzymes studied; the level of total free thiol groups was lowered; and a cross- over between hexose monophosphates and fructose diphosphate was induced. The original activities of the enzymes and metabolic processes inhibited were restored coincidentally with the reappearance of growth of the cells. Inhibition of G-6-PDH, PFK and of an early step in the oxidation of NAD(P)H appeared to be determinative for the growth. In the cells inhibited transiently by iodocetate, GAPDH and ADH were the most sensitive enzymes. The activity of the latter but not of the former was readily restored. The R.Q. was lowered, and was restored later than growth. The cells which recovered from the inhibition by iodoacetate appeared to be physiologically different from the control.

ANTIMICROBIAL PROPERTIES OF CERTAIN GLUCOSAMINE DERIVATIVES.

Forty glucosamine derivatives were tested for antimicrobial properties. Five of these were shown to possess significant activity against a number of bacteria, yeasts, and fungi in vitro. These were 5-bromosalicylidene-D-glucosamine (No. 103), cinnamylidene-D-glucosamine (No. 112), 3,5-dibromosalicylidene-D-glucosamine (No. 104), 3,5-dibromosalicylidene-D-glucosamine oxime (No. 130), and 3-nitro-5-chlorosalicylidene-D-glucosamine (No. 119). The acute LD50 of each compound in mice was approximately 200, 400, 400, 600, and &gt; 1000 mg/kg for 119, 104, 130, 103, and 112, respectively. Studies on mode of action indicated that 103, 104, and 130 may interfere with glucosamine metabolism in Candida albicans; ultrastructural changes in this organism were also produced by these three derivatives. Numbers 103, 104, 119, and 112 were phosphorylated by yeast hexokinase, and all except 112 depressed the rate of glycolysis in a cell-free extract.

Studies on the mode of action of antifungal agents

A study was conducted to determine the mode of action of antifungal agents in respect to the relationships between the antifungal activities and morphological effects, drug resistance and their effects on the metabolism of pathogenic fungi. The results obtained were as follows : The antifungal activities and morphological effects of 36 compounds were tested against 8 different strains of pathogenic fungi, such as Trichophyton, Aspergillus, Candida, etc. by the agar plate-streaking method. These compounds can be classified into 6 groups in terms of the relationships between the antifungal activities and morphological effects. Several compounds which showed strong antifungal activity exhibited a griseofulvin-like action on the fungi, a morphologic change. In view of such results obtained, the examination of an in vitro antifungal activity of drugs should be tested in addition to observing any morphologic changes which occur. The newly isolated strains of fungi were first examined for their susceptibility to nystatin, amphotericin B, trichomycin, variotin and merzonin; Trichophyton mentagrophytes, T. rubrum and Aspergillus fumigatus showed, more or less, differences in susceptibilities to these drugs. The differences in susceptibilities observed may have depended upon the strains employed; A. fumigatus was especially conspicuous in this sense. All of the test drugs employed did not produce a significant degree of increase to resistance in all strains of A. fumigatus tested. The population of the resistant cells of A. fumigatus was determined by the replica plating method. Cells which were highly resistant to amphotericin B or trichomycin were much more numerous than those resistant to nystatin, variotin or merzonin, and the drug resistance of these isolated cells were stable as demonstrated by ten successive transfers on drug-free agar media. Thus, it might be concluded that the pathogenic fungi have a difficulty in acquiring drug resistance to antifungal agents; however, the existence of highly resistant strains and cells may demonstrate the acquisition of an increase in drug resistance, similar to bacteria and other microorganisms, if such drugs were to be used extensively. The effects of antifungal agents, especially polyene antibiotics, such as nystatin, trichomycin and amphotericin B, and, also, for comparison, pentachlorophenol, a synthetic drug, on the metabolism of Candida albicans or Candida pseudotropicalis were investigated in preliminary experiments in order to determine the primary action of these antifungal agents. The endogenous respiration, the O2 uptake by the utilization of glucose, the 32P-phosphate incorporation into the cells and into several kinds of metabolites, and the incorporation of 14C-amino acids mixture into the cells were examined in the presence of antifungal agents of concentration which inhibited the growth of 50% or more cells. Neither stimulation nor inhibition was observed in the endogenous respiration and the O2 uptake by the oxidation of glucose in the presence of the employed drugs. The incorporation of 32P-phosphate into the cells was markedly suppressed by these drugs, especially by the polyene antibiotics. Marked suppression of the incorporation of 32P-phosphate into the TCA-soluble fraction and a slight inhibition of it into the phospholipid and RNA fractions were demonstrated. The incorporation of 14C-amino acids into the cells was also inhibited.

Candida albicansの二形現象と物質代謝

Candida albicansの二形現象と物質代謝