DNA array analysis ofCandida albicansgene expression in response to adherence to polystyrene

Inhibition of cell cycle-dependent hyphal and biofilm formation by a novel cytochalasin 19,20‑epoxycytochalasin Q in Candida albicans

Biofilm-mediated drug resistance is a key virulence factor of pathogenic microbes that cause a serious global health threat especially in immunocompromised individuals. Here, we investigated the antihyphal and antibiofilm activity of 19,20‑epoxycytochalasin Q (ECQ), a cytochalasin actin inhibitor isolated from medicinal mushroom Xylaria sp. BCC1067 against Candida albicans. Remarkably, 256 µg/ml of ECQ inhibited over 95% of C. albicans hyphal formation after 24 h-treatment. Combined ECQ and lipid-based biosurfactant effectively enhanced the antihyphal activity, lowering required ECQ concentrations. Hyphal fragmentation and reduction of biofilm biomass, shown by SEM and AFM visualization of ECQ-treated biofilms, were well corelated to the reduced metabolic activities of young and 24 h-preformed C. albicans biofilms. Induced intracellular accumulation of reactive oxygen species (ROS) also occurred in accompany with the leakage of shrunken cell membrane and defective cell wall at increasing ECQ concentrations. Transcriptomic analyses via RNA-sequencing revealed a massive change (> 1300 genes) in various biological pathways, following ECQ-treatment. Coordinated expression of genes, associated with cellular response to drugs, filamentous growth, cell adhesion, biofilm formation, cytoskeleton organization, cell division cycle, lipid and cell wall metabolisms was confirmed via qRT-PCR. Protein-protein association tool identified coupled expression between key regulators of cell division cyclin-dependent kinases (Cdc19/28) and a gamma-tubulin (Tub4). They coordinated ECQ-dependent hyphal specific gene targets of Ume6 and Tec1 during different phases of cell division. Thus, we first highlight the antihyphal and antibiofilm property of the novel antifungal agent ECQ against one of the most important life-threatening fungal pathogens by providing its key mechanistic detail in biofilm-related fungal infection.

Proteomic profile of Candida albicans biofilm

Candida albicans biofilms are characterized by structural and cellular heterogeneity that confers antifungal resistance and immune evasion. Despite this, biofilm formation remains poorly understood. In this study, we used proteomic analysis to understand biofilm formation in C. albicans related to morphophysiological and architectural features. LC-MS/MS analysis revealed that 64 proteins were significantly modulated, of which 31 were upregulated and 33 were downregulated. The results indicate that metabolism (25 proteins), gene expression (13 proteins), stress response (7 proteins), and cell wall (5 proteins) composition are modulated. The rate of oxidative phosphorylation (OxPhos) and biosynthesis of UDP-N-acetylglucosamine, vitamin B6, and thiamine increased, while the rate of methionine biosynthesis decreased. There was a significant modification of the cell wall architecture due to higher levels of Sun41, Pir1 and Csh1 and increased glycosylation of proteins. It was observed that C. albicans induces hyphal growth by upregulating the expression of genes involved in cAMP-PKA and MAPK pathways. This study is significant in that it suggests an increase in OxPhos and alteration of cell wall architecture that could be contributing to the recalcitrance of C. albicans cells growing in biofilms. Nevertheless, a deeper investigation is needed to explore it further. SIGNIFICANCE: Candida sps is included in the list of pathogens with potential drug resistance threat due to the increased frequency especially colonization of medical devices, and tissues among the patients, in recent years. Significance of our study is that we are reporting traits like modulation in cell wall composition, amino acid and vitamin biosynthesis and importantly energy generation (OxPhos) etc. These traits could be conferring antifungal resistance, host immune evasion etc. and thus survival, in addition to facilitating biofilm formation. These findings are expected to prime the further studies on devising potent strategy against biofilm growth among the patients.

Suppressive effects of 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymer on the adherence of Candida species and MRSA to acrylic denture resin

Objectives

The effects of 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymer on the adherence of microorganisms such as non-Candida albicans Candida (NCAC) and methicillin-resistant Staphylococcus aureus (MRSA), frequently detected in oral infections in immunocompromised and/or elderly people, to denture resin material, are still unclear. Here, we report the effects of MPC-polymer on the adherence of C. albicans, NCAC, and MRSA to acrylic denture resin.

Methods

Sixteen strains of C. albicans, seven strains of C. glabrata, two strains of C. tropicalis, one strain of C. parapsilosis, and six strains of MRSA were used. We cultured the fungal/bacterial strains and examined the cell growth and adherence of fungi/bacteria to mucin-coated acrylic denture resin plates (ADRP) with or without MPC-polymer coating, by scanning electron microscopy. The cell surface hydrophobicity of the fungal/bacterial strains was measured by the adsorption to hydrocarbons.

Results

MPC-polymer did not affect the growth of all strains of Candida species and MRSA, but significantly suppressed adherence to ADRP in most strains of C. albicans and all strains of NCAC and MRSA. A significant positive correlation was found between cell hydrophobicity and the reduction rates of microbial adherence to ADRP treated with 5% of MPC-polymer.

Conclusions

MPC-polymer treatment for acrylic resin material suppresses the adherence of C. albicans, NCAC and MRSA via their hydrophilicity interaction.

Clinical significance

The application of MPC-polymer for denture hygiene is potent to prevent oral candidiasis, denture stomatitis and opportunistic infection, caused by Candida species and MRSA, via suppressing the adherence of those fungus/bacteria.

Identifying Candida albicans Gene Networks Involved in Pathogenicity

Candida albicans is a normal member of the human microbiome. It is also an opportunistic pathogen, which can cause life-threatening systemic infections in severely immunocompromized individuals. Despite the availability of antifungal drugs, mortality rates of systemic infections are high and new drugs are needed to overcome therapeutic challenges including the emergence of drug resistance. Targeting known disease pathways has been suggested as a promising avenue for the development of new antifungals. However, <30% of C. albicans genes are verified with experimental evidence of a gene product, and the full complement of genes involved in important disease processes is currently unknown. Tools to predict the function of partially or uncharacterized genes and generate testable hypotheses will, therefore, help to identify potential targets for new antifungal development. Here, we employ a network-extracted ontology to leverage publicly available transcriptomics data and identify potential candidate genes involved in disease processes. A subset of these genes has been phenotypically screened using available deletion strains and we present preliminary data that one candidate, PEP8, is involved in hyphal development and immune evasion. This work demonstrates the utility of network-extracted ontologies in predicting gene function to generate testable hypotheses that can be applied to pathogenic systems. This could represent a novel first step to identifying targets for new antifungal therapies.

Serial Systemic Candida albicans Infection Highlighted by Proteomics

Candida albicans is the major pathogen isolated from nosocomial bloodstream infections, leading to higher mortality rates. Thus, due to its clinical relevance, studies aiming to understand host–pathogen interactions in C. albicans infection are necessary. Therefore, we performed proteomic analysis using a murine model of serial systemic infection by C. albicans to evaluate possible changes in the protein profile of the pathogen over time. Firstly, we observed a reduction in the median survival time of infected animals with increasing passage number, suggesting a higher pathogenicity acquired during repeated infections. By LC-MS/MS, it was possible to obtain protein profiles from the wild-type strain (WT) and compare them to proteins extracted from Candida cells recovered from infected tissues during passages one, three, and four (P1, P3, and P4). We obtained 56, 29, and 97 proteins in P1, P3, P4, respectively, all varying in abundance. Regarding biological processes, the majority of proteins were related to carbohydrate metabolism, stress responses and amino acid metabolism. The proteins were also categorized according to their potential role in virulence traits, such as biofilm production, yeast-to-hyphae transition, phenotypic switching, proteins related to stress responses, and uncharacterized proteins. Therefore, serial infection in combination with proteomic approach enabled us to deepen the existing knowledge about host-pathogen interactions.

Fungal-specific subunits of the Candida albicans mitochondrial complex I drive diverse cell functions including cell wall synthesis

Our published research has focused on the role of Goa1p, an apparent regulator of the Candida albicans mitochondrial complex I (CI). Lack of Goa1p affects optimum cell growth, CI activity and virulence. Eukaryotic CI is composed of a core of 14 alpha-proteobacterial subunit proteins and a variable number of supernumerary subunit proteins. Of the latter group of proteins, one (NUZM) is fungal specific and the other (NUXM) is found in fungi, algae and plants, but is not a mammalian CI subunit protein. We have established that NUXM is orf19.6607 and NUZM is orf19.287 in C. albicans. Herein, we validate both subunit proteins as NADH:ubiquinone oxidoreductases (NUO) and annotate their gene functions. To accomplish these objectives, we compared null mutants of each with wild type (WT) and gene-reconstituted strains. Genetic mutants of genes NUO1 (orf19.6607) and NUO2 (orf19.287), not surprisingly, each had reduced oxygen consumption, decreased mitochondrial redox potential, decreased CI activity, increased reactive oxidant species (ROS) and decreased chronological ageing in vitro. Loss of either gene results in disassembly of CI. Transcriptional profiling of both mutants indicated significant down-regulation of genes of carbon metabolism, as well as up-regulation of mitochondrial-associated gene families that may occur to compensate for the loss of CI activity. Profiling of both mutants also demonstrated a loss of cell wall β-mannosylation but not in a conserved CI subunit (ndh51Δ). The profiling data may indicate specific functions driven by the enzymatic activity of Nuo1p and Nuo2p. Of importance, each mutant is also avirulent in a murine blood-borne, invasive model of candidiasis associated with their reduced colonization of tissues. Based on their fungal specificity and roles in virulence, we suggest both as drug targets for antifungal drug discovery.

Human serum potentiates the expression of genes associated with antifungal drug resistance in C. albicans biofilms on central venous catheters

Candida albicans is a major agent of fungaemias and frequently causes systemic disease through seeded, blood stream dissemination. These infections, particularly common in hospitalized patients with central venous catheters (CVCs), appear to persevere due to biofilm reservoirs of the yeast that tend to develop on the device. Although it is known that candidal biofilms are intrinsically resistant to antifungals compared with their planktonic counterparts, there is a paucity of data on the expression of antifungal drug resistance genes (DRGs) in candidal biofilms in CVC reservoirs. Furthermore, notwithstanding the fact that CVCs are constantly bathed in human serum, there are no studies on the effect of the latter on the DRG expression in candidal biofilms. Hence, we developed in vitro biofilms of three different C. albicans strains on silicone CVC discs immersed in human serum and evaluated the temporal expression of nine antifungal DRGs. In an attempt to evaluate the effect of hyphal elements on DRG expression, we incorporated a hyphal mutant (HM) and its wild-type (WT) counterpart, as well as a fresh clinical isolate in the studies. Human serum significantly up-regulated DRG transcripts in Candida biofilms on CVCs, at different stages of biofilm growth, while the WT strain over-expressed more DRGs than the HM strain. Here, we report, for the first time, that both human serum and the hyphal elements of the yeast have a profound modulatory effect on DRG expression in C. albicans biofilms on CVCs.

Human serum promotes Candida albicans biofilm growth and virulence gene expression on silicone biomaterial

Objectives

Systemic candidal infections are a common problem in hospitalized patients due to central venous catheters fabricated using silicone biomaterial (SB). We therefore evaluated the effect of human serum on C. albicans biofilm morphology, growth, and the expression of virulence-related genes on SB in vitro.

Methods

We cultivated C. albicans SC5314 (wild-type strain, WT) and its derivative HLC54 (hyphal mutant, HM) for 48 h in various conditions, including the presence or absence of SB discs, and human serum. The growth of planktonic and biofilm cells of both strains was monitored at three time points by a tetrazolium salt reduction assay and by scanning electron microscopy. We also analyzed by RT-PCR its expression of the virulence-related genes ALS3, HWP1, EAP1, ECE1, SAP1 - SAP10, PLB1, PLB2, PLC and PLD.

Results

At each time point, planktonic cells of WT strain cultured in yeast nitrogen base displayed a much higher expression of EAP1 and HWP1, and a moderately higher ALS3 expression, than HM cells. In planktonic cells, expression of the ten SAP genes was higher in the WT strain initially, but were highly expressed in the HM strain by 48 h. Biofilm growth of both strains on SB was promoted in the presence of human serum than in its absence. Significant upregulation of ALS3, HWP1, EAP1, ECE1, SAP1, SAP4, SAP6 - SAP10, PLB1, PLB2 and PLC was observed for WT biofilms grown on serum-treated SB discs for at least one time point, compared with biofilms on serum-free SB discs.

Conclusions

Human serum stimulates C. albicans biofilm growth on SB discs and upregulates the expression of virulence genes, particularly adhesion genes ALS3 and HWP1, and hydrolase-encoding genes SAP, PLB1 and PLB2. This response is likely to promote the colonization of this versatile pathogen within the human host.

Intermolecular interactions of the malate synthase of Paracoccidioides spp

Background

The fungus Paracoccidioides spp is the agent of paracoccidioidomycosis (PCM), a pulmonary mycosis acquired by the inhalation of fungal propagules. Paracoccidioides malate synthase (PbMLS) is important in the infectious process of Paracoccidioides spp because the transcript is up-regulated during the transition from mycelium to yeast and in yeast cells during phagocytosis by murine macrophages. In addition, PbMLS acts as an adhesin in Paracoccidioides spp. The evidence for the multifunctionality of PbMLS indicates that it could interact with other proteins from the fungus and host. The objective of this study was to identify and analyze proteins that possibly bind to PbMLS (PbMLS-interacting proteins) because protein interactions are intrinsic to cell processes, and it might be possible to infer the function of a protein through the identification of its ligands.

Results

The search for interactions was performed using an in vivo assay with a two-hybrid library constructed in S. cerevisiae; the transcripts were sequenced and identified. In addition, an in vitro assay using pull-down GST methodology with different protein extracts (yeast, mycelium, yeast-secreted proteins and macrophage) was performed, and the resulting interactions were identified by mass spectrometry (MS). Some of the protein interactions were confirmed by Far-Western blotting using specific antibodies, and the interaction of PbMLS with macrophages was validated by indirect immunofluorescence and confocal microscopy. In silico analysis using molecular modeling, dynamics and docking identified the amino acids that were involved in the interactions between PbMLS and PbMLS-interacting proteins. Finally, the interactions were visualized graphically using Osprey software.

Conclusion

These observations indicate that PbMLS interacts with proteins that are in different functional categories, such as cellular transport, protein biosynthesis, modification and degradation of proteins and signal transduction. These data suggest that PbMLS could play different roles in the fungal cell.

Comparative transcriptome analysis of Paracoccidioides brasiliensis during in vitro adhesion to type I collagen and fibronectin: identification of potential adhesins

Paracoccidioidomycosis is caused by the dimorphic fungus Paracoccidioides brasiliensis. The extracellular matrix (ECM) plays an important role in regulation of cell adhesion, differentiation, migration and proliferation of cells. An in vitro binding assay of P. brasiliensis yeast cells adhering to type I collagen and fibronectin was performed in order to identify novel adhesins. Representational difference analysis (RDA) was employed to identify genes upregulated under adhesion-inducing conditions. Expressed sequence tags (ESTs) from cDNA libraries generated by the RDA technique were analyzed. Genes related to functional categories, such as metabolism, transcription, energy, protein synthesis and fate, cellular transport and biogenesis of cellular components were upregulated. Transcripts encoding the P. brasiliensis protein enolase (PbEno) and the high-affinity cooper transporter (PbCtr3) were identified and further characterized. The recombinant enolase (rPbEno) and a synthetic peptide designed for PbCtr3 were obtained and demonstrated to be able to bind ECM components. Immunofluorescence assays demonstrated that rPbEno specifically binds to the macrophage surface, reinforcing the role of this molecule in the P. brasiliensis interaction with host cells. In addition, upregulation of selected genes was demonstrated by qRT-PCR. In synthesis, the strategy can be useful in characterization of potential P. brasiliensis adhesins.

Adherence of Candida albicans and Candida parapsilosis to epithelial cells correlates with fungal cell surface carbohydrates

Many studies have described the adherence of Candida albicans to epithelial cells but little is known about Candida parapsilosis adhesion and its role in host cell surface recognition. This study was designed to evaluate the correlation between the adherence of 20 C. albicans and 12 C. parapsilosis strains to human buccal epithelial cells and the expression of fungal cell surface carbohydrates using lectin histochemistry. Adherence assays were carried out by incubating epithelial cells in yeast suspensions (10(7) cells ml(-1) ) and peroxidase conjugated lectins (Con A, WGA, UEA I and PNA at 25 μg ml(-1) ) were used for lectin histochemistry. The results showed that adherence was overall greater for C. albicans than for C. parapsilosis (P < 0.01) and that the individual strain differences correlated with a high content of cell surface α-l-fucose residues as indicated by the UEA I staining pattern. Based on the saccharide specificity of the lectins used, these results suggest that l-fucose residues on cell surface glycoconjugates may represent recognition molecules for interactions between the yeast strain studied and the host (r = 0.6985, P = 0.0045). In addition, our results indicated the presence of α-d-glucose/α-d-mannose, N-acetyl-D-glucosamine/N-acetylneuraminic acid and D-galactose/N-acetyl-D-galactosamine in fungal cell wall.

Response of sessile cells to stress: from changes in gene expression to phenotypic adaptation

A better understanding of the genotypic and phenotypic adaptation of sessile (biofilm-associated) microorganisms to various forms of stress is required in order to develop more effective antibiofilm strategies. This review presents an overview of what high-throughput transcriptomic analyses have taught us concerning the response of various clinically relevant microorganisms (including Pseudomonas aeruginosa, Burkholderia cenocepacia and Candida albicans) to treatment with antibiotics or disinfectants. In addition, several problems associated with identifying gene expression patterns in biofilms in general and their implications for identifying the response to stress are discussed (with a focus on heterogeneity in microbial biofilms and the role of small RNAs in microbial group behavior).

A Candida albicans early stage biofilm detachment event in rich medium

BACKGROUND

Dispersal from Candida albicans biofilms that colonize catheters is implicated as a primary factor in the link between contaminated catheters and life threatening blood stream infections (BSI). Appropriate in vitro C. albicans biofilm models are needed to probe factors that induce detachment events.

RESULTS

Using a flow through system to culture C. albicans biofilms we characterized a detachment process which culminates in dissociation of an entire early stage biofilm from a silicone elastomer surface. We analyzed the transcriptome response at time points that bracketed an abrupt transition in which a strong adhesive association with the surface is weakened in the initial stages of the process, and also compared batch and biofilm cultures at relevant time points. K means analysis of the time course array data revealed categories of genes with similar patterns of expression that were associated with adhesion, biofilm formation and glycoprotein biosynthesis. Compared to batch cultures the biofilm showed a pattern of expression of metabolic genes that was similar to the C. albicans response to hypoxia. However, the loss of strong adhesion was not obviously influenced by either the availability of oxygen in the medium or at the silicone elastomer surface. The detachment phenotype of mutant strains in which selected genes were either deleted or overexpressed was characterized. The microarray data indicated that changes associated with the detachment process were complex and, consistent with this assessment, we were unable to demonstrate that transcriptional regulation of any single gene was essential for loss of the strong adhesive association.

CONCLUSION

The massive dispersal of the early stage biofilm from a biomaterial surface that we observed is not orchestrated at the level of transcriptional regulation in an obvious manner, or is only regulated at this level by a small subpopulation of cells that mediate adhesion to the surface.

Candida albicans cell wall proteins

The Candida albicans cell wall maintains the structural integrity of the organism in addition to providing a physical contact interface with the environment. The major components of the cell wall are fibrillar polysaccharides and proteins. The proteins of the cell wall are the focus of this review. Three classes of proteins are present in the candidal cell wall. One group of proteins attach to the cell wall via a glycophosphatidylinositol remnant or by an alkali-labile linkage. A second group of proteins with N-terminal signal sequences but no covalent attachment sequences are secreted by the classical secretory pathway. These proteins may end up in the cell wall or in the extracellular space. The third group of proteins lack a secretory signal, and the pathway(s) by which they become associated with the surface is unknown. Potential constituents of the first two classes have been predicted from analysis of genome sequences. Experimental analyses have identified members of all three classes. Some members of each class selected for consideration of confirmed or proposed function, phenotypic analysis of a mutant, and regulation by growth conditions and transcription factors are discussed in more detail.

CTA4 transcription factor mediates induction of nitrosative stress response in Candida albicans

This work has identified regulatory elements in the major fungal pathogen Candida albicans that enable response to nitrosative stress. Nitric oxide (NO) is generated by macrophages of the host immune system and commensal bacteria, and the ability to resist its toxicity is one adaptation that promotes survival of C. albicans inside the human body. Exposing C. albicans to NO induces upregulation of the flavohemoglobin Yhb1p. This protein confers protection by enzymatically converting NO to harmless nitrate, but it is unknown how C. albicans is able to detect NO in its environment and thus initiate this defense only as needed. We analyzed this problem by incrementally mutating the YHB1 regulatory region to identify a nitric oxide-responsive element (NORE) that is required for NO sensitivity. Five transcription factor candidates of the Zn(II)2-Cys6 family were then isolated from crude whole-cell extracts by using magnetic beads coated with this DNA element. Of the five, only deletion of the CTA4 gene prevented induction of YHB1 transcription during nitrosative stress and caused growth sensitivity to the NO donor dipropylenetriamine NONOate; Cta4p associates in vivo with NORE DNA from the YHB1 regulatory region. Deletion of CTA4 caused a small but significant decrease in virulence. A CTA4-dependent putative sulfite transporter encoded by SSU1 is also implicated in NO response, but C. albicans ssu1 mutants were not sensitive to NO, in contrast to findings in Saccharomyces cerevisiae. Cta4p is the first protein found to be necessary for initiating NO response in C. albicans.

Candida albicans VPS1 contributes to protease secretion, filamentation, and biofilm formation

To investigate the pre-vacuolar secretory pathway in Candida albicans, we cloned and analyzed the C. albicans homolog of the Saccharomyces cerevisiae vacuolar protein sorting gene VPS1. C. albicans VPS1 encodes a predicted 694-aa dynamin-like GTPase that is 73.3% similar to S. cerevisiae Vps1p. Plasmids bearing C. albicans VPS1 complemented the temperature-sensitive growth, abnormal class F vacuolar morphology, and carboxypeptidase missorting of a S. cerevisiae vps1 null mutant. To study VPS1 function in C. albicans, a conditional mutant strain (tetR-VPS1) was generated by deleting the first allele of VPS1 and placing the second allele under control of a tetracycline-regulatable promoter. With doxycycline, the tetR-VPS1 mutant was hyper-susceptible to sub-inhibitory concentrations of fluconazole, but not amphotericin B, 5-fluorocytosine, or non-specific osmotic stresses. The repressed tetR-VPS1 mutant was defective in filamentation and secreted less extracellular protease activity. Biofilm production and filamentation within the biofilm were markedly reduced. These results suggest that C. albicans VPS1 has a key role in several important virulence-related phenotypes.

Proteomic analysis reveals metabolic changes during yeast to hypha transition in Yarrowia lipolytica

Fungal dimorphism is important for survival in different environments and has been related to virulence. The ascomycete Yarrowia lipolytica can grow as yeast, pseudomycelial or mycelial forms. We have used a Y. lipolytica parental strain and a Deltahoy1 mutant, which is unable to form hypha, to set up a model for dimorphism and to characterize in more depth the yeast to hypha transition by proteomic techniques. A two-dimensional gel electrophoresis (2-DE) based differential expression analysis of Y. lipolytica yeast and hyphal cells was performed, and 45 differentially expressed proteins were detected; nine with decreased expression in hyphal cells were identified. They corresponded to the S. cerevisiae homologues of Imd4p, Pdx3p, Cdc19, Sse1p, Sol3p, Sod2p, Xpt1p, Mdh1p and to the unknown protein YALIOB00924g. Remarkably, most of these proteins are involved in metabolic pathways, with four showing oxidoreductase activity. Furthermore, taking into account that this is the first report of 2-DE analysis of Y. lipolytica protein extracts, 35 more proteins from the 2D map of soluble yeast proteins, which were involved in metabolism, cell rescue, energy and protein synthesis, were identified.

Disruption of Candida albicans IFF4 gene involves modifications of the cell electrical surface properties

During the past two decades, the prevalence of candidiasis has increased markedly and Candida albicans has now become one of the most important causes of nosocomial infections, especially after colonization of inert surfaces such as catheters or prostheses. In a previous report, we demonstrated the overexpression of 35 unidentified genes in response to adherence of C. albicans germ tubes to plastic. Therefore, a bioinformatic analysis was performed searching for genes encoding surface proteins potentially involved in adherence. Nineteen genes were thus selected, and one of them, CaIFF4, was further investigated. The deduced protein of this CaIFF4 gene revealed a glycosylphosphatidylinositol (GPI)-anchored site as well as the presence of a N-terminal signal peptide. Disruption of both alleles of CaIFF4 gene from C. albicans parent strain BWP17 was performed by PCR method. Then investigations of properties of null mutant for CaIFF4 gene showed a decrease of adherence of germ tubes to plastic in comparison to the parent strain BWP17. Besides, electrophoretic mobilities of germ tubes of CaIFF4 null mutant and of parental strain BWP17 were measured. Data were then analysed with soft particles analysis theory. Results point out a less important electrophoretic mobility of germ tubes of CaIFF4 null mutant in comparison to germ tubes of BWP17 parental strain.

Optimized candidal biofilm microtiter assay

Microtiter based candidal biofilm formation is commonly being used. Here we describe the analysis of factors influencing the development of candidal biofilms such as the coating with serum, growth medium and pH. The data reported here show that optimal candidal biofilm formation is obtained when grown in unbuffered YNB at pH 7, in wells that have been coated with Fetal Calf Serum or Fetal Bovine Serum.

Development and evaluation of different normalization strategies for gene expression studies in Candida albicans biofilms by real-time PCR

BACKGROUND

Candida albicans biofilms are commonly found on indwelling medical devices. However, the molecular basis of biofilm formation and development is not completely understood. Expression analysis of genes potentially involved in these processes, such as the ALS (Agglutinine Like Sequence) gene family can be performed using quantitative PCR (qPCR). In the present study, we investigated the expression stability of eight housekeeping genes potentially useful as reference genes to study gene expression in Candida albicans (C. albicans) biofilms, using the geNorm Visual Basic Application (VBA) for Microsoft Excel. To validate our normalization strategies we determined differences in ALS1 and ALS3 expression levels between C. albicans biofilm cells and their planktonic counterparts.

RESULTS

The eight genes tested in this study are ranked according to their expression stability (from most stable to least stable) as follows: ACT1 (beta-actin)/PMA1 (adenosine triphosphatase), RIP (ubiquinol cytochrome-c reductase complex component), RPP2B (cytosolic ribosomal acidic protein P2B), LSC2 (succinyl-CoA synthetase beta-subunit fragment), IMH3 (inosine-5'-monophosphate dehydrogenase fragment), CPA1 (carbamoyl-phosphate synthethase small subunit) and GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Our data indicate that five genes are necessary for accurate and reliable normalization of gene expression data in C. albicans biofilms. Using different normalization strategies, we found a significant upregulation of the ALS1 gene and downregulation of the ALS3 gene in C. albicans biofilms grown on silicone disks in a continous flow system, the CDC reactor (Centre for Disease Control), for 24 hours.

CONCLUSION

In conclusion, we recommend the use of the geometric mean of the relative expression values from the five housekeeping genes (ACT1, PMA1, RIP, RPP2B and LSC2) for normalization, when analysing differences in gene expression levels between C. albicans biofilm cells and planktonic cells. Validation of the normalization strategies described above showed that the ALS1 gene is overexpressed and the ALS3 gene is underexpressed in C. albicans biofilms grown on silicone in the CDC reactor for 24 hours.