Although morphological plasticity is a central virulence trait of Candida albicans, the number of filament-associated genes and the interplay of mechanisms regulating their expression remain unknown. By correlation-based network modeling of the transcriptional response to different defined external stimuli for morphogenesis we identified a set of eight genes with highly correlated expression patterns, forming a core filamentation response. This group of genes included ALS3, ECE1, HGT2, HWP1, IHD1 and RBT1 which are known or supposed to encode for cell- wall associated proteins as well as the Rac1 guanine nucleotide exchange factor encoding gene DCK1 and the unknown function open reading frame orf19.2457. The validity of network modeling was confirmed using a dataset of advanced complexity that describes the transcriptional response of C. albicans during epithelial invasion as well as comparing our results with other previously published transcriptome studies. Although the set of core filamentation response genes was quite small, several transcriptional regulators are involved in the control of their expression, depending on the environmental condition.
Candida albicans, a common fungal pathogen which diverged from the baker’s yeast Saccharomyces cerevisiae has the unique ability to utilise N-acetylglucosamine, an amino sugar and exhibits phenotypic differences. It has acquired intricate regulatory mechanisms at different levels in accordance with its life style. N-acetylglucosamine kinase, a component of the N-acetylglucosamine catabolic cascade is an understudied gene since Saccharomyces cerevisiae lacks it. We report HXK1 to act as both positive and negative regulator of transcription of genes involved in maintaining cellular homeostasis. It is involved in repression of hyphal specific genes in addition to metabolic genes. Its regulation of filamentation and GlcNAc metabolism is independent of the known classical regulators like EFG1, CPH1, RAS1, TPK2 or TUP1. Moreover, Hxk1-GFP is localised to cytoplasm, nucleus and mitochondria in a condition specific manner. By employing two-step affinity purification, we report the interaction of HXK1 with SIR2 under filamentation inducing conditions. Our work highlights a novel regulatory mechanism involved in filamentation repression and attempts to decipher the GlcNAc catabolic regulatory cascade in eukaryotes.
microRNAs (miRNAs), endogenous posttranscriptional repressors by base-pairing of their cognate mRNAs in plants and animals, have mostly been thought lost in the kingdom of fungi. Here, we report the identification of miRNAs from the fungus Cryptococcus neoformans. With bioinformatics and Northern blotting approaches, we found that these miRNAs and their hairpin precursors were present in this fungus. The size of miR1 and miR2 is 22 nt and 18 nt, respectively. The precursors are about ∼70 nt in length that is close to mammalian pre-miRNAs. Characteristic features of miRNAs are also found in miR1/2. We demonstrated that the identified miRNAs, miR1 and miR2, caused transgene silencing via the canonical RNAi pathway. Bioinformantics analysis helps to reveal a number of identical sequences of the miR1/2 in transposable elements (TEs) and pseudogenes, prompting us to think that fungal miRNAs might be involved in the regulation of the activity of transposons and the expression of pseudogenes. This study identified functional miRNAs in C. neoformans, and sheds light on the diversity and evolutionary origin of eukaryotic miRNAs.
Genomic plasticity is a mechanism for adaptation to environmental cues such as host responses and antifungal drug pressure in many fungi including the human pathogenic yeast Candida glabrata. In this study we evaluated the phenotypic and genotypic stability of the world-wide used C. glabrata reference strain CBS138/ATCC2001 under laboratory conditions. A set of ten lineages of this wild type strain and genetically modified progenies were obtained from different scientific laboratories, and analyzed for genotypic and phenotypic alterations. Even though the derivates were indistinguishable by multi locus sequence typing, different phenotypic groups that correlated with specific karyotypic changes were observed. In addition, modifications in the adherence capacity to plastic surface emerged that were shown to correlate with quantitative changes in adhesin gene expression rather than subtelomeric gene loss or differences in the number of macrosatellite repeats within adhesin genes. These results confirm the genomic plasticity of C. glabrata and show that chromosomal aberrations and functional adaptations may occur not only during infection and under antimicrobial therapy, but also under laboratory conditions without extreme selective pressures. These alterations can significantly affect phenotypic properties such as cell surface attributes including adhesion and the cell wall carbohydrate composition and therefore, if unnoticed, may adulterate the outcome of genetic studies.
Candida glabrata owes its success as a pathogen, in part, to a large repertoire of adhesins present on the cell surface. Our current knowledge of C. glabrata adhesins and their role in the interaction between host and pathogen is limited to work with only a single family of epithelial adhesins (Epa proteins). Here we report identification and characterization of a family of glycosylphosphatidylinositol (GPI) anchored cell wall proteins in C. glabrata. These proteins are absent in both S. cerevisiae and C. albicans suggesting that C. glabrata has evolved different mechanism(s) for interaction with host cells. In the current study we present data on the characterization of Pwp7p (PA14 domain containing Wall Protein) and Aed1p (Adherence to Endothelial cells) of this family in the interaction of C. glabrata with Human Umbilical Vein Endothelial Cells (HUVECs). Deletion of C. glabrata genes PWP7 and AED1 results in significant reduction in adherence to endothelial cells compared to the wild type parent. These data indicate that C. glabrata utilizes these proteins for adherence to endothelial cells in vitro. This also represents the first evidence that C. glabrata utilizes adhesins other than Epa proteins.
Candida; GPI; adhesin; PWP7; AED1; AED2
The intracellular enzyme urea amidolyase (Dur1,2p) enables C. albicans to utilize urea as a sole nitrogen source. Because deletion of the DUR1,2 gene reduces survival of C. albicans co-cultured with a murine macrophage cell line, we investigated the role of Dur1,2p in pathogenesis using a mouse model of disseminated candidiasis. A dur1,2Δ/dur1,2Δ strain was significantly less virulent than the wild-type strain, showing significantly higher survival rate, better renal function, and decreased and less sustained fungal colonization in kidney and brain. Complementation of the mutant restored virulence. DUR1,2 deletion resulted in a milder host inflammatory reaction. Immunohistochemistry, flow cytometry, and magnetic resonance imaging showed decreased phagocytic infiltration into infected kidneys. Systemic cytokine levels of wild-type mice infected with the dur1,2 mutant showed a more balanced systemic pro-inflammatory cytokine response. Host gene expression and protein analysis in infected kidneys revealed parallel changes in the local immune response. Significant differences were observed in the kidney IL-1 inflammatory pathway, IL-15 signaling, MAP kinase signaling, and the alternative complement pathway. We conclude that Dur1,2p is important for kidney colonization during disseminated candidiasis and contributes to an unbalanced host inflammatory response and subsequent renal failure. Therefore, this Candida-specific enzyme may represent a useful drug target to protect the host from kidney damage associated with disseminated candidiasis.
Understanding multicellular fungal structures is important for designing better strategies against human fungal pathogens. For example, the ability to form multicellular biofilms is a key virulence property of the yeast Candida albicans. C. albicans biofilms form on indwelling medical devices and are drug resistant, causing serious infections in hospital settings. Multicellular fungal communities are heterogeneous, consisting of cells experiencing different environments. Heterogeneity is likely important for the phenotypic characteristics of communities, yet it is poorly understood. Here we used colonies of the yeast Saccharomyces cerevisiae as a model fungal multicellular structure. We fractionated the outside colony layers from the cells in the center by FACS, using a Cit1-GFP marker expressed exclusively on the outside. Transcriptomics analysis of the two subpopulations revealed that the outside colony layers are actively growing by fermentative metabolism, while the cells residing on the inside are in a resting state and experience changes to mitochondrial activity. Our data shows several parallels with C. albicans biofilms providing insight into the contributions of heterogeneity to biofilm phenotypes. Hallmarks of C. albicans biofilms – the expression of ribosome and translation functions and activation of glycolysis and ergosterol biosynthesis occur on the outside of colonies, while expression of genes associates with sulfur assimilation is observed in the colony center. Cell wall restructuring occurs in biofilms, and cell wall functions are enriched in both fractions: the outside cells display enrichment of cell wall biosynthesis enzymes and cell wall proteins, while the inside cells express cell wall degrading enzymes. Our study also suggests that noncoding transcription and posttranscriptional mRNA regulation play important roles during growth of yeast in colonies, setting the scene for investigating these pathways in the development of multicellular fungal communities.
Candida albicans is the most frequently encountered human fungal pathogen, causing both superficial infections and life-threatening systemic diseases. Functional genomic studies performed in this organism have mainly used knock-out mutants and extensive collections of overexpression mutants are still lacking. Here, we report the development of a first generation C. albicans ORFeome, the improvement of overexpression systems and the construction of two new libraries of C. albicans strains overexpressing genes for components of signaling networks, in particular protein kinases, protein phosphatases and transcription factors. As a proof of concept, we screened these collections for genes whose overexpression impacts morphogenesis or growth rates in C. albicans. Our screens identified genes previously described for their role in these biological processes, demonstrating the functionality of our strategy, as well as genes that have not been previously associated to these processes. This article emphasizes the potential of systematic overexpression strategies to improve our knowledge of regulatory networks in C. albicans. The C. albicans plasmid and strain collections described here are available at the Fungal Genetics Stock Center. Their extension to a genome-wide scale will represent important resources for the C. albicans community.
The ability of Candida albicans to survive in the presence of nitrosative stress during the initial contact with the host immune system is crucial for its ability to colonize mammalian hosts. Thus, this fungus must activate robust mechanisms to neutralize and repair nitrosative-induced damage. Until now, very little was known regarding the regulatory circuits associated with reactive nitrogen species detoxification in fungi. To gain insight into the transcriptional regulatory networks controlling nitrosative stress response (NRS) in C. albicans a compilation of transcriptional regulator-defective mutants were screened. This led to the identification of Cwt1p as a negative regulator of NSR. By combining genome-wide location and expression analyses, we have characterized the Cwt1p regulon and demonstrated that Cwt1p is directly required for proper repression of the flavohemoglobin Yhb1p, a key NO-detoxification enzyme. Furthermore, Cwt1p operates both by activating and repressing genes of specific functions solicited upon NSR. Additionally, we used Gene Set Enrichment Analysis to reinvestigate the C. albicans NSR-transcriptome and demonstrate a significant similarity with the transcriptional profiles of C. albicans interacting with phagocytic host-cells. In summary, we have characterized a novel negative regulator of NSR and bring new insights into the transcriptional regulatory network governing fungal NSR.
The human opportunistic pathogen Candida albicans undergoes a reversible morphological transition between the yeast and hyphal states in response to a variety of signals. One such environmental trigger is growth within a semisolid matrix such as agar medium. This growth condition is of interest because it may mimic the growth of C. albicans in contact with host tissue during infection. During growth within a semisolid matrix, hyphal growth is positively regulated by the transcriptional regulator Czf1p and negatively by a second key transcriptional regulator, Efg1p. Genetic studies indicate that Czf1p, a member of the zinc-cluster family of transcriptional regulators, exerts its function by opposing the inhibitory influence of Efg1p on matrix-induced filamentous growth. We examined the importance of the two known activities of Czf1p, DNA-binding and interaction with Efg1p. We found that the two activities were separable by mutation allowing us to demonstrate that the DNA-binding activity of Czf1p was essential for its role as a positive regulator of morphogenesis. Surprisingly, however, interactions with Efg1p appeared to be largely dispensable. Our studies provide the first evidence of a key role for the DNA-binding activity of Czf1p in the morphological yeast-to-hyphal transition triggered by matrix-embedded growth.
Small heat shock proteins (sHsps) have multiple cellular functions. However, the biological function of sHsps in pathogenic microorganisms is largely unknown. In the present study we identified and characterized the novel sHsp Hsp21 of the human fungal pathogen Candida albicans. Using a reverse genetics approach we demonstrate the importance of Hsp21 for resistance of C. albicans to specific stresses, including thermal and oxidative stress. Furthermore, a hsp21Δ/Δ mutant was defective in invasive growth and formed significantly shorter filaments compared to the wild type under various filament-inducing conditions. Although adhesion to and invasion into human-derived endothelial and oral epithelial cells was unaltered, the hsp21Δ/Δ mutant exhibited a strongly reduced capacity to damage both cell lines. Furthermore, Hsp21 was required for resisting killing by human neutrophils. Measurements of intracellular levels of stress protective molecules demonstrated that Hsp21 is involved in both glycerol and glycogen regulation and plays a major role in trehalose homeostasis in response to elevated temperatures. Mutants defective in trehalose and, to a lesser extent, glycerol synthesis phenocopied HSP21 deletion in terms of increased susceptibility to environmental stress, strongly impaired capacity to damage epithelial cells and increased sensitivity to the killing activities of human primary neutrophils. Via systematic analysis of the three main C. albicans stress-responsive kinases (Mkc1, Cek1, Hog1) under a range of stressors, we demonstrate Hsp21-dependent phosphorylation of Cek1 in response to elevated temperatures. Finally, the hsp21Δ/Δ mutant displayed strongly attenuated virulence in two in vivo infection models. Taken together, Hsp21 mediates adaptation to specific stresses via fine-tuning homeostasis of compatible solutes and activation of the Cek1 pathway, and is crucial for multiple stages of C. albicans pathogenicity. Hsp21 therefore represents the first reported example of a small heat shock protein functioning as a virulence factor in a eukaryotic pathogen.
The pathogenic fungus Candida albicans switches from yeast growth to filamentous growth in response to genotoxic stresses, in which phosphoregulation of the checkpoint kinase Rad53 plays a crucial role. Here we report that the Pph3/Psy2 phosphatase complex, known to be involved in Rad53 dephosphorylation, is required for cellular responses to the DNA-damaging agent methyl methanesulfonate (MMS) but not the DNA replication inhibitor hydroxyurea (HU) in C. albicans. Deletion of either PPH3 or PSY2 resulted in enhanced filamentous growth during MMS treatment and continuous filamentous growth even after MMS removal. Moreover, during this growth, Rad53 remained hyperphosphorylated, MBF-regulated genes were downregulated, and hypha-specific genes were upregulated. We have also identified S461 and S545 on Rad53 as potential dephosphorylation sites of Pph3/Psy2 that are specifically involved in cellular responses to MMS. Therefore, our studies have identified a novel molecular mechanism mediating DNA damage response to MMS in C. albicans.
The next generation magnetic nanoparticles (MNPs) with theranostic applications have attracted significant attention and will greatly improve nanomedicine in cancer therapeutics. Such novel MNP formulations must have ultra-low particle size, high inherent magnetic properties, effective imaging, drug targeting, and drug delivery properties. To achieve these characteristic properties, a curcumin-loaded MNP (MNP-CUR) formulation was developed.
MNPs were prepared by chemical precipitation method and loaded with curcumin (CUR) using diffusion method. The physicochemical properties of MNP-CUR were characterized using dynamic light scattering, transmission electron microscopy, and spectroscopy. The internalization of MNP-CUR was achieved after 6 hours incubation with MDA-MB-231 breast cancer cells. The anticancer potential was evaluated by a tetrazolium-based dye and colony formation assays. Further, to prove MNP-CUR results in superior therapeutic effects over CUR, the mitochondrial membrane potential integrity and reactive oxygen species generation were determined. Magnetic resonance imaging capability and magnetic targeting property were also evaluated.
MNP-CUR exhibited individual particle grain size of ~9 nm and hydrodynamic average aggregative particle size of ~123 nm. Internalized MNP-CUR showed a preferential uptake in MDA-MB-231 cells in a concentration-dependent manner and demonstrated accumulation throughout the cell, which indicates that particles are not attached on the cell surface but internalized through endocytosis. MNP-CUR displayed strong anticancer properties compared to free CUR. MNP-CUR also amplified loss of potential integrity and generation of reactive oxygen species upon treatment compared to free CUR. Furthermore, MNP-CUR exhibited superior magnetic resonance imaging characteristics and significantly increased the targeting capability of CUR.
MNP-CUR exhibits potent anticancer activity along with imaging and magnetic targeting capabilities. This approach can be extended to preclinical and clinical use and may have importance in cancer treatment and cancer imaging in the future. Further, if these nanoparticles can functionalize with antibody/ligands, they will serve as novel platforms for multiple biomedical applications.
magnetic nanoparticles; drug delivery systems; magnetic resonance imaging; nanomedicine; cancer therapeutics; biomedical applications
We report here the identification and characterization of a previously uncharacterized, two-component response regulator gene (orf19.5843) from Candida albicans. Because of its apparent functions in stress adaptation, we have named this gene SRR1 (stress response regulator 1). Disruption of SRR1 causes defects in hyphal development, reduced resistance to stress, and severe virulence attenuation in the mouse model of disseminated candidiasis.
Acquired resistance to antifungal agents now supports the introduction of susceptibility testing for species-drug combinations for which this was previously thought unnecessary. For pathogenic yeasts, conventional phenotypic testing needs at least 24 h. Culture on a porous aluminum oxide (PAO) support combined with microscopy offers a route to more rapid results.
Microcolonies of Candida species grown on PAO were stained with the fluorogenic dyes Fun-1 and Calcofluor White and then imaged by fluorescence microscopy. Images were captured by a charge-coupled device camera and processed by publicly available software. By this method, the growth of yeasts could be detected and quantified within 2 h. Microcolony imaging was then used to assess the susceptibility of the yeasts to amphotericin B, anidulafungin and caspofungin (3.5 h culture), and voriconazole and itraconazole (7 h culture).
Overall, the results showed good agreement with EUCAST (86.5% agreement; n = 170) and E-test (85.9% agreement; n = 170). The closest agreement to standard tests was found when testing susceptibility to amphotericin B and echinocandins (88.2 to 91.2%) and the least good for the triazoles (79.4 to 82.4%). Furthermore, large datasets on population variation could be rapidly obtained. An analysis of microcolonies revealed subtle effects of antimycotics on resistant strains and below the MIC of sensitive strains, particularly an increase in population heterogeneity and cell density-dependent effects of triazoles. Additionally, the method could be adapted to strain identification via germ tube extension. We suggest PAO culture is a rapid and versatile method that may be usefully adapted to clinical mycology and has research applications.
The fungus C. albicans uses adhesins to interact with human epithelial surfaces in the processes of colonization and pathogenesis. The C. albicans ALS (agglutinin-like sequence) gene family encodes eight large cell-surface glycoproteins (Als1-Als7 and Als9) that have adhesive function. This study utilized C. albicans Δals mutant strains to investigate the role of the Als family in oral epithelial cell adhesion and damage, cytokine induction and activation of a MAPK-based (MKP1/c-Fos) signaling pathway that discriminates between yeast and hyphae. Of the eight Δals mutants tested, only the Δals3 strain showed significant reductions in oral epithelial cell adhesion and damage, and cytokine production. High fungal:epithelial cell multiplicities of infection were able to rescue the cell damage and cytokine production phenotypes, demonstrating the importance of fungal burden in mucosal infections. Despite its adhesion, damage and cytokine induction phenotypes, the Δals3 strain induced MKP1 phosphorylation and c-Fos production to a similar extent as control cells. Our data demonstrate that Als3 is involved directly in epithelial adhesion but indirectly in cell damage and cytokine induction, and is not the factor targeted by oral epithelial cells to discriminate between the yeast and hyphal form of C. albicans.
Candida albicans is an opportunistic pathogen that proliferates in the intestinal tract of critically ill patients where it continues to be a major cause of infectious-related mortality. The precise cues that shift intestinal C. albicans from its ubiquitous indolent colonizing yeast form to an invasive and lethal filamentous form remain unknown. We have previously shown that severe phosphate depletion develops in the intestinal tract during extreme physiologic stress and plays a major role in shifting intestinal Pseudomonas aeruginosa to express a lethal phenotype via conserved phosphosensory-phosphoregulatory systems. Here we studied whether phosphate dependent virulence expression could be similarly demonstrated for C. albicans. C. albicans isolates from the stool of critically ill patients and laboratory prototype strains (SC5314, BWP17, SN152) were evaluated for morphotype transformation and lethality against C. elegans and mice during exposure to phosphate limitation. Isolates ICU1 and ICU12 were able to filament and kill C. elegans in a phosphate dependent manner. In a mouse model of intestinal phosphate depletion (30% hepatectomy), direct intestinal inoculation of C. albicans caused mortality that was prevented by oral phosphate supplementation. Prototype strains displayed limited responses to phosphate limitation; however, the pho4Δ mutant displayed extensive filamentation during low phosphate conditions compared to its isogenic parent strain SN152, suggesting that mutation in the transcriptional factor Pho4p may sensitize C. albicans to phosphate limitation. Extensive filamentation was also observed in strain ICU12 suggesting that this strain is also sensitized to phosphate limitation. Analysis of the sequence of PHO4 in strain ICU12, its transcriptional response to phosphate limitation, and phosphatase assays confirmed that ICU12 demonstrates a profound response to phosphate limitation. The emergence of strains of C. albicans with marked responsiveness to phosphate limitation may represent a fitness adaptation to the complex and nutrient scarce environment typical of the gut of a critically ill patient.
Background & objectives:
HIV infection is characterized by a perturbation in T cell homeostasis, leading to alteration in T cell subsets. In addition to alteration in differentiation, HIV infection also leads to change in T cell survival and regenerative capacity, as suggested by differential expression of CD127 and CD57. We evaluated the expression patterns of CD127 and CD57 on CD4 and CD8 effector, memory and naïve T cell subsets in HIV-infected and uninfected individuals.
We characterized T cell subsets based on expression of these markers, and compared their expression pattern in HIV infected subjects and uninfected controls. We further assessed therapy generated changes in these subsets and expression of CD127 and CD57 on them.
There was a generalized decrease in naïve CD4 and CD8 T cells in HIV infected subjects. These changes in T cell subset distribution were related to antigen load. CD127 expression was significantly reduced in T cells from HIV infected subject. In association to this, HIV infected subjects had higher percentage of T cell subsets expressing CD57. Increased CD57 and reduced CD127 expression correlated with plasma viraemia and CD8 T cell activation state. Incomplete restoration of T cell subset proportions was observed, despite suppression of viral replication and increase in CD4 T cell counts. Further, the improvement was more pronounced in CD127 expression.
Interpretation & conclusions:
HIV infected subjects have reduced T cell regenerative capacity along with increased senescence, highlighting decreased proliferation and effector activities.
CD57; CD127; HIV-1 viral load; T cell activation; T cell subset
Recent studies report curcumin nanoformulation(s) based on polylactic-co-glycolic acid (PLGA), β-cyclodextrin, cellulose, nanogel, and dendrimers to have anticancer potential. However, no comparative data are currently available for the interaction of curcumin nanoformulations with blood proteins and erythrocytes. The objective of this study was to examine the interaction of curcumin nanoformulations with cancer cells, serum proteins, and human red blood cells, and to assess their potential application for in vivo preclinical and clinical studies.
The cellular uptake of curcumin nanoformulations was assessed by measuring curcumin levels in cancer cells using ultraviolet-visible spectrophotometry. Protein interaction studies were conducted using particle size analysis, zeta potential, and Western blot techniques. Curcumin nanoformulations were incubated with human red blood cells to evaluate their acute toxicity and hemocompatibility.
Cellular uptake of curcumin nanoformulations by cancer cells demonstrated preferential uptake versus free curcumin. Particle sizes and zeta potentials of curucumin nanoformulations were varied after human serum albumin adsorption. A remarkable capacity of the dendrimer curcumin nanoformulation to bind to plasma protein was observed, while the other formulations showed minimal binding capacity. Dendrimer curcumin nanoformulations also showed higher toxicity to red blood cells compared with the other curcumin nanoformulations.
PLGA and nanogel curcumin nanoformulations appear to be very compatible with erythrocytes and have low serum protein binding characteristics, which suggests that they may be suitable for application in the treatment of malignancy. These findings advance our understanding of the characteristics of curcumin nanoformulations, a necessary component in harnessing and implementing improved in vivo effects of curcumin.
nanoparticle; curcumin; chemotherapy; cellular uptake; protein binding; hemocompatibility
The opportunistic human pathogenic fungus Aspergillus fumigatus is able to produce the dark brown pigment pyomelanin by degradation of L-tyrosine. Pyomelanin was shown to protect the fungus against reactive oxygen intermediates as well as cell wall disturbing compounds and is therefore assumed to protect against immune effector cells during the infection process. Several genes for tyrosine degradation and pyomelanin formation are organized in a cluster in the genome of A. fumigatus. Here, we aimed at further analyzing tyrosine degradation and a possible role of pyomelanin in virulence. For this purpose, the function of two not yet characterized genes of the cluster, i.e., hmgX and hmgR, was analyzed. Generation of corresponding gene deletion mutants and reconstituted strains revealed that hmgX and hmgR are essential for tyrosine degradation. Both mutants, ΔhmgX and ΔhmgR, were not able to use tyrosine as sole carbon or nitrogen source and revealed impaired pyomelanin production. HmgR harbors a Zn(II)2Cys6-DNA binding domain. Analyses of the steady state mRNA levels revealed that HmgR acts as a transcriptional activator for the genes of the tyrosine degradation cluster. Consistently, an HmgR-eGFP fusion protein was localized in the nucleus of A. fumigatus cells. By contrast, HmgX was found to be localized in the cytoplasm and does not contribute to regulation of gene transcription. HPLC analyses showed that HmgX is crucial for the conversion of p-hydroxyphenylpyruvate to homogentisic acid, the main intermediate in pyomelanin formation. Thus, HmgX is supposed to function as an accessory factor to mediate specific activity of HppD. Remarkably, the ability to degrade tyrosine and to form pyomelanin is dispensable for virulence of A. fumigatus in a murine infection model.
Timely access to antiretroviral therapy is a key to controlling HIV infection. Late diagnosis and presentation to care diminish the benefits of antiretrovirals and increase risk of transmission. We aimed to identify late presenters in patients sent for first CD4 T cell count after HIV diagnosis, for therapy initiation evaluation. Further we aimed at identifying patient factors associated with higher risk of late presentation.
Retrospective data collection and analysis was done for 3680 subjects visiting the laboratory for CD4 T cell counts between 2001 and 2007. We segregated the patients on basis of their CD4 T cell counts after first HIV diagnosis. Factors associated with risk of late presentation to CD4 T cell counts after HIV diagnosis were identified using univariate analysis, and the strength of association of individual factor was assessed by calculation of odds ratios.
Of 3680 subjects, 2936 (83.37%) were defined as late presenters. Late testing varied among age groups, transmission categories, and gender. Males were twice as likely to present late as compared to females. We found significant positive association of heterosexual transmission route (p < 0.001), and older age groups of 45 years and above (p = 0.0004) to late presentation. Female sex, children below 14 years of age and sexual contact with HIV positive spouse were associated with significantly lower risks to presenting late. Intravenous drug users were also associated with lower risks of late presentation, in comparison to heterosexual transmission route.
The study identifies HIV infected population groups at a higher risk of late presentation to care and treatment. The risk factors identified to be associated with late presentation should be utilised in formulating targeted public health interventions in order to improve early HIV diagnosis.
Using a Tn7 transposon library of Candida albicans, we have identified a mutant that exhibited sensitivity in drop plate assays to oxidants such as menadione and hydrogen peroxide. To verify the role of the mutated gene in stress adaptation, null mutants were constructed and phenotypically characterized. Because of its apparent functions in growth and oxidant adaptation, we have named the gene GOA1. Goa1p appears to be unique to the CTG subclade of the Saccharomycotina, including C. albicans. Mutants of C. albicans lacking goa1 (strain GOA31) were more sensitive to 6 mM H2O2 and 0.125 mM menadione than the wild type (wt) or a gene-reconstituted (GOA32) strain. The sensitivity to oxidants correlated with reduced survival of the GOA31 mutant in human neutrophils and avirulence compared to control strains. Other phenotypes of GOA31 include reduced growth and filamentation in 10% serum, Spider, and SLAD agar media and an inability to form chlamydospores. Since Goa1p has an N-terminal mitochondrion localization site, we also show that green fluorescent protein-tagged Goa1p shows a mitochondrionlike distribution during oxidant or osmotic stress. Further, the inability of GOA31 to grow in medium containing lactate, ethanol, or glycerol as the sole carbon source indicates that the mitochondria are defective in the mutant. To determine how Goa1p contributes to mitochondrial function, we compared the wt, GOA32, and GOA31 strains for mitochondrial electrical membrane potential, respiration, and oxidative phosphorylation. We now show that GOA31, but not the wt or GOA32, had decreased respiration and mitochondrial membrane potential such that mutant cells are unable to drive oxidative phosphorylation. This is the first report in C. albicans of a respiratory defect caused by a loss of mitochondrial membrane potential.
The Ssk1p response regulator of Candida albicans is required for oxidant adaptation, survival in human neutrophils, and virulence in a disseminated murine model of candidiasis. The activities of the Ssk1p are signaled through the HOG1 MAP kinase pathway (HOG=hyperosmotic glycerol). Further, we have previously shown that the amino acid residues D556 and D513 of the Ssk1p receiver domain are critical to the activities of the Ssk1p in oxidant stress adaptation and morphogenesis. Herein, we use transcriptional profiling to explain the oxidant sensitivity and defect in morphogenesis of two point mutants (D556N and D513K, respectively) compared to a WT strain. In the D556N mutant compared to WT cells during oxidative stress (5mM H2O2), a down regulation of genes associated with redox homeostasis and oxidative stress occurred that accounted for about 5% of all gene changes, including among others, SOD1 (superoxide dismutase), CAP1 (transcription factor required for some forms of oxidant adaptation), and three genes encoding glutathione biosynthesis proteins (GLR1, GSH1, and GSH2). Mutant SSK26 (D513K) was not sensitive to peroxide but was impaired in its yeast to hyphal transition. We noted down regulation of genes associated with morphogenesis and cell elongation. Virulence of each mutant was also evaluated in a rat vaginitis model of candidiasis. Clearance of the SSK1 null mutant (strain SSK21) and SSK25 from the vaginal canal was significantly greater than wild type (CAF2-1) or the D513K mutant (D513K), indicating that a specific change in a single amino acid of the Ssk1p may alter the ability of this strain to colonize the rat vaginal mucosa.
response regulator; two-component proteins; point mutants