Microevolution of Candida glabrata (Nakaseomyces glabrata) during an infection.

Candida glabrata (Nakaseomyces glabrata) is an emergent and opportunistic fungal pathogen that colonizes and persists in different niches within its human host. In this work, we studied five clinical isolates from one patient (P7), that have a clonal origin, and all of which come from blood cultures except one, P7-3, obtained from a urine culture. We found phenotypic variation such as sensitivity to high temperature, oxidative stress, susceptibility to two classes of antifungal agents, and cell wall porosity. Only isolate P7-3 is highly resistant to the echinocandin caspofungin while the other four isolates from P7 are sensitive. However, this same isolate P7-3, is the only one that displays susceptibility to fluconazole (FLC), while the rest of the isolates are resistant to this antifungal. We sequenced the PDR1 gene which encodes a transcription factor required to induce the expression of several genes involved in the resistance to FLC and found that all the isolates encode for the same Pdr1 amino acid sequence except for the last isolate P7-5, which contains a single amino acid change, G1099C in the putative Pdr1 transactivation domain. Consistent with the resistance to FLC, we found that the CDR1 gene, encoding the main drug efflux pump in C. glabrata, is highly overexpressed in the FLC-resistant isolates, but not in the FLC-sensitive P7-3. In addition, the resistance to FLC observed in these isolates is dependent on the PDR1 gene. Additionally, we found that all P7 isolates have a different proportion of cell wall carbohydrates compared to our standard strains CBS138 and BG14. In P7 isolates, mannan is the most abundant cell wall component, whereas ß-glucan is the most abundant component in our standard strains. Consistently, all P7 isolates have a relatively low cell wall porosity compared to our standard strains. These data show phenotypic and genotypic variability between clonal isolates from different niches within a single host, suggesting microevolution of C. glabrata during an infection.

Characterization of the Trr/Trx system in the fungal pathogen Candida glabrata.

C. glabrata, an opportunistic fungal pathogen, can adapt and resist to different stress conditions. It is highly resistant to oxidant stress compared to other Candida spp and to the phylogenetically related but non-pathogen Saccharomyces cerevisiae. In this work, we describe the Trx/Trr system of C. glabrata composed of Trr1 and Trr2 (thioredoxin reductases) and Trx2 (thioredoxin) that are localized in the cytoplasm and Trx3 present in the mitochondrion. The transcriptional induction of TRR2 and TRX2 by oxidants depends on Yap1 and Skn7 and TRR1 and TRX3 have a low expression level. Both TRR2 and TRX2 play an important role in the oxidative stress response. The absence of TRX2 causes auxotrophy of methionine and cysteine. Trr1 and Trr2 are necessary for survival at high temperatures and for the chronological life span of C. glabrata. Furthermore, the Trx/Trr system is needed for survival in the presence of neutrophils. The role of TRR1 and TRX3 is not clear, but in the presence of neutrophils, they have non-overlapping functions with their TRR2 and TRX2 paralogues.

Candida glabrata Hst1-Rfm1-Sum1 complex evolved to control virulence-related genes.

C. glabrata is an opportunistic fungal pathogen and the second most common cause of opportunistic fungal infections in humans, that has evolved virulence factors to become a successful pathogen: strong resistance to oxidative stress, capable to adhere and form biofilms in human epithelial cells as well as to abiotic surfaces and high resistance to xenobiotics. Hst1 (a NAD+-dependent histone deacetylase), Sum1 (putative DNA binding protein) and Rfm1 (connector protein) form a complex (HRS-C) and control the resistance to oxidative stress, to xenobiotics (the antifungal fluconazole), and adherence to epithelial cells. Hst1 is functionally conserved within the Saccharomycetaceae family, Rfm1 shows a close phylogenetic relation within the Saccharomycetaceae family while Sum1 displays a distant phylogenetic relation with members of the family and is not conserved functionally. CDR1 encodes for an ABC transporter (resistance to fluconazole) negatively controlled by HRS-C, for which its binding site is located within 223 bp upstream from the ATG of CDR1. The absence of Hst1 and Sum1 renders the cells hyper-adherent, possibly due to the overexpression of AED1, EPA1, EPA22 and EPA6, all encoding for adhesins. Finally, in a neutrophil survival assay, HST1 and SUM1, are not required for survival. We propose that Sum1 in the HRS-C diverged functionally to control a set of genes implicated in virulence: adherence, resistance to xenobiotics and oxidative stress.

Analysis of Volatile Molecules Present in the Secretome of the Fungal Pathogen Candida glabrata.

Candida albicans, Candida glabrata, Candida parapsilosis and Candida tropicalis are the four most common human fungal pathogens isolated that can cause superficial and invasive infections. It has been shown that specific metabolites present in the secretomes of these fungal pathogens are important for their virulence. C. glabrata is the second most common isolate world-wide and has an innate resistance to azoles, xenobiotics and oxidative stress that allows this fungal pathogen to evade the immune response and persist within the host. Here, we analyzed and compared the C. glabrata secretome with those of C. albicans, C. parapsilosis, C. tropicalis and the non-pathogenic yeast Saccharomyces cerevisiae. In C. glabrata, we identified a different number of metabolites depending on the growth media: 12 in synthetic complete media (SC), 27 in SC-glutamic acid and 23 in rich media (YPD). C. glabrata specific metabolites are 1-dodecene (0.09 ± 0.11%), 2,5-dimethylundecane (1.01 ± 0.19%), 3,7-dimethyldecane (0.14 ± 0.15%), and octadecane (0.4 ± 0.53%). The metabolites that are shared with C. albicans, C. glabrata, C. parapsilosis, C. tropicalis and S. cerevisiae are phenylethanol, which is synthesized from phenylalanine, and eicosane and nonanoic acid (identified as trimethylsilyl ester), which are synthesized from fatty acid metabolism. Phenylethanol is the most abundant metabolite in all fungi tested: 26.36 ± 17.42% (C. glabrata), 46.77 ± 15.58% (C. albicans), 49.76 ± 18.43% (C. tropicalis), 5.72 ± 0.66% (C. parapsilosis.) and 44.58 ± 27.91% (S. cerevisiae). The analysis of C. glabrata's secretome will allow us to further our understanding of the possible role these metabolites could play in its virulence.

Candida glabrata peroxiredoxins, Tsa1 and Tsa2, and sulfiredoxin, Srx1, protect against oxidative damage and are necessary for virulence.

Candida glabrata is an opportunistic fungal pathogen that can cause life-threatening infections in immunocompromised patients. To ensure a successful infection, C. glabrata has evolved a variety of strategies to avoid killing within the host. One of these strategies is the resistance to oxidative stress. Here we show that the sulfiredoxin Srx1 and the peroxiredoxins, Tsa1 and Tsa2, are implicated in the oxidative stress response (OSR) and required for virulence. We analyzed null mutations in SRX1, TSA1 and TSA2 and showed that TSA2 and SRX1 are required to respond to oxidative stress. While TSA1 expression is constitutive, SRX1 and TSA2 are induced in the presence of H2O2 in a process dependent on H2O2 concentration and on both transcription factors Yap1 and Skn7. Msn2 and Msn4 are not necessary for the regulation of SRX1, TSA1 and TSA2. Interestingly, TSA1 and TSA2, which are localized in the cytoplasm, are induced in the presence of neutrophils and required for survival in these phagocytic cells.

Npa3/ScGpn1 carboxy-terminal tail is dispensable for cell viability and RNA polymerase II nuclear targeting but critical for microtubule stability and function.

Genetic deletion of the essential GTPase Gpn1 or replacement of the endogenous gene by partial loss of function mutants in yeast is associated with multiple cellular phenotypes, including in all cases a marked cytoplasmic retention of RNA polymerase II (RNAPII). Global inhibition of RNAPII-mediated transcription due to malfunction of Gpn1 precludes the identification and study of other cellular function(s) for this GTPase. In contrast to the single Gpn protein present in Archaea, eukaryotic Gpn1 possesses an extension of approximately 100 amino acids at the C-terminal end of the GTPase domain. To determine the importance of this C-terminal extension in Saccharomyces cerevisiae Gpn1, we generated yeast strains expressing either C-terminal truncated (gpn1ΔC) or full-length ScGpn1. We found that ScGpn1ΔC was retained in the cell nucleus, an event physiologically relevant as gpn1ΔC cells contained a higher nuclear fraction of the RNAPII CTD phosphatase Rtr1. gpn1ΔC cells displayed an increased size, a delay in mitosis exit, and an increased sensitivity to the microtubule polymerization inhibitor benomyl at the cell proliferation level and two cellular events that depend on microtubule function: RNAPII nuclear targeting and vacuole integrity. These phenotypes were not caused by inhibition of RNAPII, as in gpn1ΔC cells RNAPII nuclear targeting and transcriptional activity were unaffected. These data, combined with our description here of a genetic interaction between GPN1 and BIK1, a microtubule plus-end tracking protein with a mitotic function, strongly suggest that the ScGpn1 C-terminal tail plays a critical role in microtubule dynamics and mitotic progression in an RNAPII-independent manner.

Molecular characterization of the silencing complex SIR in Candida glabrata hyperadherent clinical isolates.

An important virulence factor for the fungal pathogen Candida glabrata is the ability to adhere to the host cells, which is mediated by the expression of adhesins. Epa1 is responsible for ∼95% of the in vitro adherence to epithelial cells and is the founding member of the Epa family of adhesins. The majority of EPA genes are localized close to different telomeres, which causes transcriptional repression due to subtelomeric silencing. In C. glabrata there are three Sir proteins (Sir2, Sir3 and Sir4) that are essential for subtelomeric silencing. Among a collection of 79 clinical isolates, some display a hyperadherent phenotype to epithelial cells compared to our standard laboratory strain, BG14. These isolates also express several subtelomeric EPA genes simultaneously. We cloned the SIR2, SIR3 and SIR4 genes from the hyperadherent isolates and from the BG14 and the sequenced strain CBS138 in a replicative vector to complement null mutants in each of these genes in the BG14 background. All the SIR2 and SIR4 alleles tested from selected hyper-adherent isolates were functional and efficient to silence a URA3 reporter gene inserted in a subtelomeric region. The SIR3 alleles from these isolates were also functional, except the allele from isolate MC2 (sir3-MC2), which was not functional to silence the reporter and did not complement the hyperadherent phenotype of the BG14 sir3Δ. Consistently, sir3-MC2 allele is recessive to the SIR3 allele from BG14. Sir3 and Sir4 alleles from the hyperadherent isolates contain several polymorphisms and two of them are present in all the hyperadherent isolates analyzed. Instead, the Sir3 and Sir4 alleles from the BG14 and another non-adherent isolate do not display these polymorphisms and are identical to each other. The particular combination of polymorphisms in sir3-MC2 and in SIR4-MC2 could explain in part the hyperadherent phenotype displayed by this isolate.

P2X7 from j774 murine macrophages acts as a scavenger receptor for bacteria but not yeast.

We studied the effects of extracellular ATP and Ca2+ on uptake of bacteria (Staphylococcus aureus or Escherichia coli) and live yeast (Candida glabrata) by J774 macrophages to determine the role of endogenous P2X7 receptors in phagocytosis. Our findings show that phagocytosis of bio-particles coated with S. aureus or E. coli was blocked by ATP and the P2X7 receptor agonist BzATP, while yeast phagocytosis was not. A438079, an antagonist of P2X7 receptors, partially reverted the effects of ATP on bacterial phagocytosis. To determine if P2X7-mediated Ca2+ entry into macrophages was blocking the engulfment of bacteria, we measured phagocytic activity in the absence or presence of 2 mM extracellular Ca2+ with or without ATP. Ca2+, in the absence of ATP, was required for engulfment of E. coli and C. glabrata but not S. aureus. Adding ATP inhibited phagocytosis of S. aureus and E. coli regardless of Ca2+, suggesting that Ca2+ entry was not important for inhibiting phagocytosis. On the other hand, phagocytosis of normal or hyper-adherent C. glabrata mutants had an absolute requirement for extracellular Ca2+ due to yeast adhesion to macrophages mediated by Ca2+-dependent adhesion proteins. We conclude that unstimulated P2X7 from J774 cells act as scavenger receptor for the uptake of S. aureus and E. coli but not of yeast; Ca2+ entry via P2X7 receptors play no role in phagocytosis of S. aureus and E. coli; while the effect of Ca2+ on C. glabrata phagocytosis was mediated by the adhesins Epa1, Epa6 and Epa7.

Candida glabrata binds to glycosylated and lectinic receptors on the coronary endothelial luminal membrane and inhibits flow sense and cardiac responses to agonists.

Candida glabrata (CG) is an opportunistic fungal pathogen that initiates infection by binding to host cells via specific lectin-like adhesin proteins. We have previously shown the importance of lectin-oligosaccharide binding in cardiac responses to flow and agonists. Because of the lectinic-oligosaccharide nature of CG binding, we tested the ability of CG to alter the agonist- and flow-induced changes in cardiac function in isolated perfused guinea pig hearts. Both transmission and scanning electron microscopy showed strong attachment of CG to the coronary endothelium, even after extensive washing. CG shifted the coronary flow vs. auricular-ventricular (AV) delay relationship upward, indicating that greater flow was required to achieve the same AV delay. This effect was completely reversed with mannose, partially reversed with galactose and N-acetylgalactosamine, but hyaluronan had no effect. Western blot analysis was used to determine binding of CG to isolated coronary endothelial luminal membrane (CELM) receptors, and the results indicate that flow-sensitive CELM receptors, ANG II type I, α-adrenergic 1A receptor, endothelin-2, and VCAM-1 bind to CG. In addition, CG inhibited agonist-induced effects of bradykinin, angiotensin, and phenylephrine on AV delay, coronary perfusion pressure, and left ventricular pressure. Mannose reversed the inhibitory effects of CG on the agonist responses. These results suggest that CG directly binds to flow-sensitive CELM receptors via lectinic-oligosaccharide interactions with mannose and disrupts the lectin-oligosaccharide binding necessary for flow-induced cardiac responses.

Candida glabrata encodes a longer variant of the mating type (MAT) alpha2 gene in the mating type-like MTL3 locus, which can form homodimers.

The fungal pathogen Candida glabrata is a haploid asexual yeast. Candida glabrata contains orthologs of the genes that control mating and cell-type identity in other fungi, which encode putative transcription factors localized in the MAT locus in Saccharomyces cerevisiae or MTL in other fungi. Candida glabrata contains three copies of the CgMTL locus but only CgMTL1 correctly expresses the information encoded in it. CgMTL1 can encode the Cg A1: gene ( A: information), or the Cgalpha1 and Cgalpha2 genes (alpha information). CgMTL2 contains an identical copy of the Cg A1: gene. CgMTL3 contains an identical copy of the Cgalpha1 gene but a longer variant of the Cgalpha2 gene that we termed Cgalpha3. In S. cerevisiae diploid cells, that express Sc A: and Scalpha information, Sc A1: and Scalpha2 proteins form a heterodimer, which represses genes expressed only in haploid cells and some genes involved in stress response. We constructed C. glabrata strains that simultaneously express Cg A1: and Cgalpha2 or Cg A1: and Cgalpha3 genes. We did not find any phenotype in these strains when grown under a large variety of stress and nutritional conditions. However, we detected an interaction between Cg A1: and Cgalpha2 but not between Cg A1: and Cgalpha3 by Bimolecular Fluorescence Complementation and co-immunoprecipitation assays.

The superoxide dismutases of Candida glabrata protect against oxidative damage and are required for lysine biosynthesis, DNA integrity and chronological life survival.

The fungal pathogen Candida glabrata has a well-defined oxidative stress response, is extremely resistant to oxidative stress and can survive inside phagocytic cells. In order to further our understanding of the oxidative stress response in C. glabrata, we characterized the superoxide dismutases (SODs) Cu,ZnSOD (Sod1) and MnSOD (Sod2). We found that Sod1 is the major contributor to total SOD activity and is present in cytoplasm, whereas Sod2 is a mitochondrial protein. Both SODs played a central role in the oxidative stress response but Sod1 was more important during fermentative growth and Sod2 during respiration and growth in non-fermentable carbon sources. Interestingly, C. glabrata cells lacking both SODs showed auxotrophy for lysine, a high rate of spontaneous mutation and reduced chronological lifespan. Thus, our study reveals that SODs play an important role in metabolism, lysine biosynthesis, DNA protection and aging in C. glabrata.

The EPA2 adhesin encoding gene is responsive to oxidative stress in the opportunistic fungal pathogen Candida glabrata.

Candida glabrata has emerged as an important opportunistic pathogen in both mucosal and bloodstream infections. C. glabrata contains 67 adhesin-like glycosylphosphatidylinositol-cell-wall proteins (GPI-CWPs), which are classified into seven groups and the largest is the Epa family. Epa proteins are very diverse and their expression is differentially regulated. Like many of the EPA genes, EPA2 is localized in a subtelomeric region where it is subject to chromatin-based transcriptional silencing and its role remains largely unexplored. In this study, we show that EPA2 gene is induced specifically in vitro in the presence of oxidative stress generated by H2O2. This induction is dependent on both Yap1 and Skn7, whereas Msn4 represses EPA2 expression. Interestingly, EPA2 is not induced during phagocytosis, but its expression can be identified in the liver in a murine model of systemic infection. Epa2 has no effect on the virulence of C. glabrata. The work presented herein provides a foundation for future studies to dissect the molecular mechanism(s) by which EPA2 of C. glabrata can be induced in the presence of oxidative stress in a region subject to subtelomeric silencing.

Expression vectors for C-terminal fusions with fluorescent proteins and epitope tags in Candida glabrata.

Candida glabrata is a haploid yeast considered the second most common of the Candida species found in nosocomial infections, accounting for approximately 18% of candidemias worldwide. Even though molecular biology methods are easily adapted to study this organism, there are not enough vectors that will allow probing the transcriptional and translational activity of any gene of interest in C. glabrata. In this work we have generated a set of expression vectors to systematically tag any gene of interest at the carboxy-terminus with three different fluorophores (CFP, YFP and mCherry) or three epitopes (HA, FLAG or cMyc) independently. This system offers the possibility to generate translational fusions in three versions: under the gene's own promoter integrated in its native locus in genome, on a replicative plasmid under its own promoter, or on a replicative plasmid under a strong promoter to overexpress the fusions. The expression of these translational fusions will allow determining the transcriptional and translational activity of the gene of interest as well as the intracellular localization of the protein. We have tested these expression vectors with two biosynthetic genes, HIS3 and TRP1. We detected fluorescence under the microscope and we were able to immunodetect the fusions using the three different versions of the system. These vectors permit coexpression of several different fusions simultaneously in the same cell, which will allow determining protein-protein and protein-DNA interactions. This set of vectors adds a new toolbox to study expression and protein interactions in the fungal pathogen C. glabrata.

Local and regional chromatin silencing in Candida glabrata: consequences for adhesion and the response to stress.

Candida glabrata is a fungal pathogen frequently found as a commensal in humans. To colonize and disseminate successfully in the mammalian host, C. glabrata must detect signals within the host and reprogram gene expression to respond appropriately to hostile environmental conditions. One of the layers of regulation of expression of many virulence-related genes (adhesin-encoding genes, genes involved in response to oxidative stress and xenobiotics) is achieved through epigenetic mechanisms. Local and regional silencing is mediated by the activity of two NAD(+)-dependent histone deacetylases, Hst1 and Sir2, respectively, repressing many virulence genes. Hst1 and Sir2 interact with different repressor complexes to achieve regional or local silencing. Sir2 can associate with Sir4, which is then recruited to the telomere by Rap1 and yKu. Deacetylation of the histone tails creates high affinity binding sites for new molecules of the Sir complex, thereby spreading the silent domain over >20 kb. Many of the adhesin-encoding EPA genes are subject to this regulation. Hst1 in turn associates with the Sum1-Rfm1 complex. Sum1 is a DNA-binding protein, which recognizes specific sites at individual promoters, recruiting Hst1 to specific genes involved in the response to oxidative stress and xenobiotics, which results in their repression.

Local silencing controls the oxidative stress response and the multidrug resistance in Candida glabrata.

In Candida glabrata, the sirtuins Sir2 and Hst1 control the expression of a wide number of genes including adhesins required for host colonization and niacin transporters needed for growth. Given that these sirtuins can be inactivated during infection, we asked if their inhibition could modify the response of C. glabrata to other stressful conditions. Here, we found that deletion of HST1 decreases susceptibility of C. glabrata to fluconazole and hydrogen peroxide. The transcription factor Pdr1 and the ABC transporter Cdr1 mediated the fluconazole resistance phenotype of the hst1Δ cells, whereas the transcriptional activator Msn4 and the catalase Cta1 are necessary to provide oxidative stress resistance. We show that the transcription factor Sum1 interacts with Hst1 and participate in the regulation of these genes. Interestingly, even though C. glabrata and Saccharomyces cerevisiae are closely related phylogenetically, deletion of HST1 decreased susceptibility to fluconazole and hydrogen peroxide only in C. glabrata but not in S. cerevisiae, indicating a different transcriptional control by two similar sirtuins. Our findings suggest that Hst1 acts as a regulator of stress resistance associated-genes.

Characterization of a New Immunosuppressive and Antimicrobial Peptide, DRS-DA2, Isolated from the Mexican Frog, Pachymedusa dacnicolor.

Inflammatory and antimicrobial diseases constitute a major burden for society, and fighting them is a WHO strategic priority. Most of the treatments available to fight inflammatory diseases are anti-inflammatory drugs, such as corticosteroids or immunomodulators that lack cellular specificity and lead to numerous side effects. In addition to suppressing undesired inflammation and reducing disease progression, these drugs lessen the immune system protective functions. Furthermore, treating infectious diseases is more and more challenging due to the rise of microbial resistance to antimicrobial drugs. Thus, controlling the inflammatory process locally without compromising the ability to combat infections is an essential feature in the treatment of inflammatory diseases. We isolated three forms (DRS-DA2N, DRS-DA2NE, and DRS-DA2NEQ) of the same peptide, DRS-DA2, which belongs to the dermaseptin family, from the Mexican tree frog Pachymedusa dacnicolor. Interestingly, DRS-DA2N and DRS-DA2NEQ exhibit a dual activity by inducing the death of leukocytes as well as that of Gram-negative and Gram-positive bacteria, including multiresistant strains, without affecting other cells such as epithelial cells or erythrocytes. We showed that the death of both immune cells and bacteria is induced rapidly by DRS-DA2 and that the membrane is permeabilized, leading to the loss of membrane integrity. We also validated the capacity of DRS-DA2 to regulate the pool of inflammatory cells in vivo in a mouse model of noninfectious peritonitis. After the induction of peritonitis, a local injection of DRS-DA2N could decrease the number of inflammatory cells locally in the peritoneal cavity without inducing a systemic effect, as no changes in the number of inflammatory cells could be detected in blood or in the bone marrow. Collectively, these data suggest that this peptide could be a promising tool in the treatment of inflammatory diseases, such as inflammatory skin diseases, as it could reduce the number of inflammatory cells locally without suppressing the ability to combat infections.

Role of glutathione in the oxidative stress response in the fungal pathogen Candida glabrata.

Candida glabrata, an opportunistic fungal pathogen, accounts for 18-26 % of all Candida systemic infections in the US. C. glabrata has a robust oxidative stress response (OSR) and in this work we characterized the role of glutathione (GSH), an essential tripeptide-like thiol-containing molecule required to keep the redox homeostasis and in the detoxification of metal ions. GSH is synthesized from glutamate, cysteine, and glycine by the sequential action of Gsh1 (γ-glutamyl-cysteine synthetase) and Gsh2 (glutathione synthetase) enzymes. We first screened for suppressor mutations that would allow growth in the absence of GSH1 (gsh1∆ background) and found a single point mutation in PRO2 (pro2-4), a gene that encodes a γ-glutamyl phosphate reductase and catalyzes the second step in the biosynthesis of proline. We demonstrate that GSH is important in the OSR since the gsh1∆ pro2-4 and gsh2∆ mutant strains are more sensitive to oxidative stress generated by H2O2 and menadione. GSH is also required for Cadmium tolerance. In the absence of Gsh1 and Gsh2, cells show decreased viability in stationary phase. Furthermore, C. glabrata does not contain Saccharomyces cerevisiae high affinity GSH transporter ortholog, ScOpt1/Hgt1, however, our genetic and biochemical experiments show that the gsh1∆ pro2-4 and gsh2∆ mutant strains are able to incorporate GSH from the medium. Finally, GSH and thioredoxin, which is a second redox system in the cell, are not essential for the catalase-independent adaptation response to H2O2.

Sir3 Polymorphisms in Candida glabrata clinical isolates.

The opportunistic fungal pathogen Candida glabrata adheres tightly to epithelial cells in culture, mainly through the adhesin Epa1. EPA1 is the founding member of a family of up to 23 putative adhesin-encoding genes present in the C. glabrata genome. The majority of the EPA genes are localized close to the telomeres, where they are repressed by subtelomeric silencing that depends on the Sir, Ku, Rif1, and Rap1 proteins. EPA6 and EPA7 also encode functional adhesins that are repressed in vitro. EPA1 expression in vitro is tightly controlled both positively and negatively, and in addition, presents high cell-to-cell heterogeneity, which depends on Sir-mediated silencing. In this work, we characterized the ability to adhere to HeLa epithelial cells and the expression of several EPA genes in a collection of 79 C. glabrata clinical isolates from several hospitals in Mexico. We found 11 isolates that showed increased adherence to mammalian cells compared with our reference strain under conditions where EPA1 is not expressed. The majority of these isolates displayed over-expression of EPA1 and EPA6 or EPA7, but did not show increased biofilm formation. Sequencing of the SIR3 gene of several hyper-adherent isolates revealed that all of them contain several polymorphisms with respect to the reference strain. Interestingly, two isolates have polymorphisms in positions flanked by clusters of amino acids required for silencing in the Saccharomyces cerevisiae Sir3 protein. Our data show that there is a large variability in adhesin expression and adherence to epithelial cells among different C. glabrata clinical isolates.

Subtelomeric Chromatin Structure by Chromosome Conformation Capture (3C)-qPCR Methodology in Candida glabrata.

Chromatin architecture has an enormous impact on gene regulation, DNA replication, repair, and packaging. Chromatin is organized in a complex hierarchical manner in which distant fragments of DNA can interact with each other through DNA loops. DNA loops can interact between themselves to form topologically associated domains (TADs) that are further organized into functional compartments. In the last two decades, Chromatin Conformation Capture (3C technology) and its high-throughput derivatives allowed detailed analysis of the chromatin architecture. The 3C method is based on ligation of distant fragments brought together by DNA looping. The method analyzes a particular genomic region of interest and quantifies the interactions between a defined fragment with all the surrounding fragments of the region. It consists of four steps: (1) The long-distance interacting chromatin fragments are fixed with formaldehyde in whole cells which are then lysed; (2) the fixed chromatin is digested with a carefully chosen restriction enzymes to separate intervening DNA fragments; (3) the fragments brought into proximity by DNA looping are ligated in conditions favoring intramolecular ligation; and (4) the interactions are quantified by quantitative PCR using the TaqMan technology and unidirectional primers. Herein, we describe the use of this methodology to analyze the chromatin conformation at a subtelomeric locus containing three genes encoding adhesins and several cis-regulatory elements, in the pathogenic yeast Candida glabrata.

Subtelomeric silencing of the MTL3 locus of Candida glabrata requires yKu70, yKu80, and Rif1 proteins.

Candida glabrata is a haploid opportunistic fungal pathogen that is phylogenetically related to Saccharomyces cerevisiae. Even though C. glabrata has no known sexual cycle, it contains, like S. cerevisiae, three mating type-like loci (MTL) called MTL1, MTL2, and MTL3, as well as most of the genes required for mating, meiosis, and sporulation. MTL1 is localized at an internal position on chromosome B and is thought to be the locus corresponding to the MAT locus in S. cerevisiae. MTL2 and MTL3 are localized close to two telomeres on different chromosomes (29.4 kb from Chr E-L and 10.5 kb from Chr B-L, respectively). By using URA3 reporter gene insertions at the three MTL loci, we found that in contrast to the case for S. cerevisiae, only MTL3 is subject to transcriptional silencing while MTL2 is transcriptionally active, and this is in agreement with previously reported data. We found that the silencing of MTL3 is nucleated primarily at the left telomere of chromosome B and spreads over 12 kb to MTL3, rather than nucleating at flanking, closely positioned cis-acting silencers, like those flanking HMR and HML of S. cerevisiae. Interestingly, the silencing of MTL3 absolutely requires the yKu70, yKu80, and Rif1 proteins, in sharp contrast to the silencing of the HM loci of S. cerevisiae. In addition, we found that several cell type-specific genes are expressed in C. glabrata regardless of the presence, or even absence, of mating type information at any of the MTL loci.