Immunochemical characterization of Candida albicans cell wall antigens: specific determinant of Candida albicans serotype A mannan

We investigated the chemical structure of the specific determinant in the mannan of Candida albicans M-1012 (serotype A) strain. Acetolysis of the mannan, obtained by alkali extraction and purified as the copper complex, gave mannose and six oligosaccharides (from di- to hexasaccharide) and a small amount of a heptasaccharide. We examined the inhibition by these oligosaccharides up to hexaose of the precipitin reaction between anti-factor 6 serum specific for serotype A and homologous mannan, and found that the mannohexaose was the most effective inhibitor. These, and results obtained by proton magnetic resonance (PMR) spectroscopy, methylation analysis, and other structural studies, suggest that the main component of this hexaose consists of one terminal alpha (1-3) linkage in addition to four alpha (1-2) linkages, and that this alpha (1-3)-containing mannohexaose may be responsible for the specificity of antigenic factor 6. Further results obtained by analyses of polarimetry, PMR spectroscopy, and chromium trioxide oxidation-methylation of C. albicans M-1012 mannan has a beta-linkage in addition to alpha-linkages, and that the mode of the beta-linkage is mainly (1-6) linkage. Further evidence obtained by Smith degradation-methylation analysis and by quantitative precipitin reactions of intact and acid-degraded mannan suggests that the antigenic determinant of antigenic factor 6 may be bound, via the beta (1-6) linkage, to C-6 of mannose residues involved in oligosaccharide side chains of serotype A mannan.     

A characterization of pH-regulated dimorphism in Candida albicans

When cells of the dimorphic yeast Candida albicans are grown to stationary phase in defined liquid medium at 25°C, they accumulate as singlets in G_l of the cell cycle. When these pluripotent, stationary phase singlets are released into fresh medium at 37°C, they synchronously evaginate after an average period of 135 to 140 minutes and form either buds or mycelia, depending upon the pH of the medium into which they are released. This method of dimorphic regulation offers the distinct advantage of comparability and serves as a very precise method for temporal comparisons of molecular and cytological events related to the establishment of the alternate growth phenotypes. In the present report, we have carefully examined the effects of individually varying pH or temperature on the length of the pre-evagination period, the population synchrony for evagination, and the phenotype of daughter cells. Exact phenotypic transition points, optima, and upper limits are defined for both temperature and pH. In addition, a method of pH-regulated dimorphism is developed in which the original temperature shift is removed from the inductive process. Finally, a common transition phenotype is described for cells reverting from the initial mycelial to budding phenotype when either pH or temperature traverse their respective transition points. The advantages as well as limitations of pH-regulated dimorphism are discussed in detail.     

The effect of aculeacin A and papulacandin B on morphology and cell wall ultrastructure in Candida albicans

Transmission (TEM) and scanning electron microscopy (SEM) of Candida albicans cultures treated with the cell wall active antibiotics aculeacin A and papulacandin B (10 micrograms/mL) revealed highly distorted, wrinkled, and collapsed cells. Dividing cells failed to separate properly and aggregates of enlarged and elongated forms were often seen. TEM sections revealed thick and layered cell walls in the treated cultures and bud cross walls failed to segregate completely. Approximately 20% of the cells demonstrated complete cell necrosis accompanied with cytoplasmic deterioration, layered and distorted walls, and improperly formed buds and scars.     

Regulatory mechanisms controlling morphology and pathogenesis in Candida albicans

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A study of the Candida albicans cell wall proteome

Considering the importance of proteins in the structure and function of the cell wall of Candida albicans, we analyzed the cell wall subproteome of this important human pathogen by LC coupled to MS (LC-MS) using different protein extraction procedures. The analyzed samples included material extracted by hydrogen fluoride-pyridine (HF-pyridine), and whole SDS-extracted cell walls. The use of this latter innovative procedure gave similar data as compared to the analysis of HF-pyridine extracted proteins. A total of 21 cell wall proteins predicted to contain a signal peptide were identified, together with a high content of potentially glycosylated Ser/Thr residues, and the presence of a GPI motif in 19 of them. We also identified 66 "atypical" cell wall proteins that lack the above-mentioned characteristics. After tryptic removal of the most accessible proteins in the cell wall, several of the same expected GPI proteins and the most commonly found "atypical" wall proteins were identified. This result suggests that proteins are located not only at the cell wall surface, but are embedded within the cell wall itself. These results, which include new identified cell wall proteins, and comparison of proteins in blastospore and mycelial walls, will help to elucidate the C. albicans cell wall architecture.     

Effect of calcium ion uptake on Candida albicans morphology

In liquid culture using a synthetic medium, added magnesium but not calcium was required for exponential growth of Candida albicans yeast cells. However, medium without added divalent cations supported 2-3 generations of yeast growth or germ tube induction. The addition of calcium ions (1.0 mM) at any stage during the induction of germ tube formation caused reversion to a yeast mode of growth, in contrast to the effect of zinc and cobalt ions which were toxic to all growth. Inhibition of germ tube formation by calcium was not observed in the presence of either magnesium (10 microM) or manganese (100 microM). The presence of either of these ions caused inhibition of 45Ca uptake in yeast cultures. We conclude that unrestricted calcium uptake resulted in the specific inhibition of C. albicans mycelial growth, indicating a critical role for calcium in the regulation of C. albicans morphogenesis.     

家族传播的口腔白色念珠菌基因型多态性分析

目的检测家族传播的口腔白色念珠菌基因多态性。方法采集35个家庭（119个样本）的口腔牙菌斑,采用PCR ITS1-ITS2基因分型方法,检测、分析家族传播的口腔白色念珠菌基因多态性。结果 18个家庭（18/35,61%）,34个样本（34/119,28.6%）有白色念珠菌感染,11个家庭存在家族传播（11/18,61%）。在5个母子（父子）垂直传播的家庭成员中,白色念珠菌基因型均不一致。在3个呈水平传播的家庭成员中,两家基因型一致,1家不一致。在3个垂直-水平传播的家庭成员中,两家基因型一致,1家不一致。白色念珠菌家族传播基因型差异有显著统计学意义（χ2=26.571,P〈0.01）。白色念珠菌感染与年龄、性别、学历、吸烟、饮酒、义齿和龋病均无显著相关。结论白色念珠菌在口腔定植,受宿主自身遗传背景影响较大,在家族垂直传播中呈明显的基因多态性。呈水平传播的白色念珠菌菌种具有较高的传染性,基因型可保持不变。     

Variability of colonial morphology in benomyl-induced morphological mutants from Candida albicans

Abstract Colonies of Candida albicans wild-type strain 1001 were white and glossy, and this character was rather stably maintained. In contrast, 2 benomyl (methyl benzimidazole-2-yl-carbamate)-induced mutant strains, B17 and B14, that grew as long filamentous forms and displayed a rough-wrinkled colonial phenotype, switched to other colonial morphologies at significant frequencies. Clonal populations of B17 segregated smooth or sectored (rough/smooth) colonies at a frequency of 1.85%, when plated in nutrient-agar. Strains derived from these rough or smooth segregants switched back to one or the other phenotype at similar frequencies. Colonial variability in C. albicans B14 was not restricted to spontaneous switching from rough to smooth or vice versa, but eventually other types of variants, characterized as 'wavy' and 'fuzzy' were obtained, and shown to have their own capacity to switch. Smooth variants, derived from B14, were essentiallt unicellular, whereas fuzzy strains consisted only of long thin filaments, wavy and rough clones apparently being intermediate in their degree of filamentation. It is concluded that the capacity for colonial variation shown to exist in natural isolates could be activated by benomyl in others, such as 1001, which are quite stable and do not switch colonial morphology spontaneously.     

Value of morphotyping for the characterization of Candida albicans clinical isolates

Until recently, morphotyping, a method evaluating fringe and surface characteristics of streak colonies grown on malt agar, has been recommended as a simple and unexpensive typing method for Candida albicans isolates. The discriminatory power and reproducibility of Hunter's modified scheme of Phongpaichit's morphotyping has been evaluated on 28 C. albicans isolates recovered from the oral cavity of asymptomatic human immunodeficiency virus-positive subjects, and compared to two molecular typing methods: randomly amplified polymorphic DNA (RAPD) fingerprinting, and contour clamped homogeneous electric field (CHEF) electrophoretic karyotyping. Morphological features of streak colonies allowed to distinguish 11 different morphotypes while RAPD fingerprinting yielded 25 different patterns and CHEF electrophoresis recognized 9 karyotypes. The discriminatory power calculated with the formula of Hunter and Gaston was 0.780 for morphotyping, 0.984 for RAPD fingerprinting, and 0.630 for karyotyping. Reproducibility was tested using 43 serial isolates from 15 subjects (2 to 6 isolates per subject) and by repeating the test after one year storage of the isolates. While genetic methods generally recognized a single type for all serial isolates from each of the subjects studied, morphotyping detected strain variations in five subjects in the absence of genetic confirmation. Poor reproducibility was demonstrated repeating morphotyping after one year storage of the isolates since differences in at least one character were detected in 92.9% of the strains.     

Morphogenesis and cell cycle progression in Candida albicans

Candida albicans, an opportunistic human pathogen, displays three modes of growth: yeast, pseudohyphae and true hyphae, all of which differ both in morphology and in aspects of cell cycle progression. In particular, in hyphal cells, polarized growth becomes uncoupled from other cell cycle events. Yeast or pseudohyphae that undergo a cell cycle delay also exhibit polarized growth, independent of cell cycle progression. The Spitzenk?rper, an organelle composed of vesicles associated with hyphal tips, directs continuous hyphal elongation in filamentous fungal species and also in C. albicans hyphae. A polarisome mediates cell cycle dependent growth in yeast and pseudohyphae. Regulation of morphogenesis and cell cycle progression is dependent upon specific cyclins, all of which affect morphogenesis and some of which function specifically in yeast or hyphal cells. Future work will probably focus on the cell cycle checkpoints involved in connecting morphogenesis to cell cycle progression.     

A glucose sensor in Candida albicans

The Hgt4 protein of Candida albicans (orf19.5962) is orthologous to the Snf3 and Rgt2 glucose sensors of Saccharomyces cerevisiae that govern sugar acquisition by regulating the expression of genes encoding hexose transporters. We found that HGT4 is required for glucose induction of the expression of HGT12, HXT10, and HGT7, which encode apparent hexose transporters in C. albicans. An hgt4Delta mutant is defective for growth on fermentable sugars, which is consistent with the idea that Hgt4 is a sensor of glucose and similar sugars. Hgt4 appears to be sensitive to glucose levels similar to those in human serum ( approximately 5 mM). HGT4 expression is repressed by high levels of glucose, which is consistent with the idea that it encodes a high-affinity sugar sensor. Glucose sensing through Hgt4 affects the yeast-to-hyphal morphological switch of C. albicans cells: hgt4Delta mutants are hypofilamented, and a constitutively signaling form of Hgt4 confers hyperfilamentation of cells. The hgt4Delta mutant is less virulent than wild-type cells in a mouse model of disseminated candidiasis. These results suggest that Hgt4 is a high-affinity glucose sensor that contributes to the virulence of C. albicans.     

Functional characterization of myosin I tail regions in Candida albicans

The molecular motor myosin I is required for hyphal growth in the pathogenic yeast Candida albicans. Specific myosin I functions were investigated by a deletion analysis of five neck and tail regions. Hyphal formation requires both the TH1 region and the IQ motifs. The TH2 region is important for optimal hyphal growth. All of the regions, except for the SH3 and acidic (A) regions that were examined individually, were required for the localization of myosin I at the hyphal tip. Similarly, all of the domains were required for the association of myosin I with pelletable actin-bound complexes. Moreover, the hyphal tip localization of cortical actin patches, identified by both rhodamine-phalloidin staining and Arp3-green fluorescent protein signals, was dependent on myosin I. Double deletion of the A and SH3 domains depolarized the distribution of the cortical actin patches without affecting the ability of the mutant to form hyphae, suggesting that myosin I has distinct functions in these processes. Among the six myosin I tail domain mutants, the ability to form hyphae was strictly correlated with endocytosis. We propose that the uptake of cell wall remodeling enzymes and excess plasma membrane is critical for hyphal formation.     

白念珠菌铁通透酶基因CaFTH1的功能研究

[目的]白念珠菌CaFTH1是一种铁通透酶编码基因.为了研究CaFTH1对胞内铁代谢和液泡功能的影响,构建fth1△/△单基因缺失菌株和fth1△/△fet33△/△双基因缺失菌株.[方法]利用生物信息学软件对CaFTH1进行序列比对和分析;通过实时荧光定量PCR技术研究铁离子丰度对CaFTH1表达的影响;利用PCR介导的同源重组方法构建基因缺失菌株;利用原子吸收光谱方法测定基因缺失菌株胞内铁含量的变化,并对基因缺失菌株在缺铁条件和菌丝诱导条件下的生长状况进行研究;通过代谢转换实验,研究CaFTH1对细胞液泡功能的影响.[结果]序列比对结果表明白念珠菌CaFth1蛋白属于铁通透酶Ftr1超家族,与酿酒酵母液泡膜蛋白ScFth1具有最高的同源性.铁匮乏条件会诱导CaFTH1的表达,而富铁条件则会抑制其表达.白念珠菌CaFTH1的缺失会导致胞内铁含量的降低,fth1△/△突变菌株基础上CaFET33的缺失则会进一步降低胞内铁含量.在缺铁条件下,fth1△/△fet33△/△双基因缺失菌株在一定程度上表现出代谢转换能力的缺陷.另外,在某些固体菌丝诱导培养条件下,fth1△/△fet33△/△缺失菌株菌落表面形成褶皱能力显著增强;而在液体菌丝诱导条件下,则表现为增强的菌丝聚集能力.[结论]CaFTH1是一种低铁应答基因,在维持白念珠菌胞内铁离子稳态及液泡功能方面具有重要作用.CaFTH1和CaFET33基因的双缺失会对白念珠菌的菌落形态和菌丝聚集产生影响.     

Engineered control of cell morphology in vivo reveals distinct roles for yeast and filamentous forms of Candida albicans during infection

It is widely assumed that the ability of Candida albicans to switch between different morphologies is required for pathogenesis. However, most virulence studies have used mutants that are permanently locked into either the yeast or filamentous forms which are avirulent but unsuitable for discerning the role of morphogenetic conversions at the various stages of the infectious process. We have constructed a strain in which this developmental transition can be externally modulated both in vitro and in vivo. This was achieved by placing one copy of the NRG1 gene (a negative regulator of filamentation) under the control of a tetracycline-regulatable promoter. This modified strain was then tested in an animal model of hematogenously disseminated candidiasis. Mice injected with this strain under conditions permitting hyphal development succumbed to the infection, whereas all of the animals injected under conditions that inhibited this transition survived. Importantly, fungal burdens were almost identical in both sets of animals, indicating that, whereas filament formation appears to be required for the mortality resulting from a deep-seated infection, yeast cells play an important role early in the infectious process by extravasating and disseminating to the target organs. Moreover, these infecting Candida yeast cells still retained their pathogenic potential, as demonstrated by allowing this developmental transition to occur at various time points postinfection. We demonstrate here the importance of morphogenetic conversions in C. albicans pathogenesis. This engineered strain should provide a useful tool in unraveling the individual contributions of the yeast and filamentous forms at various stages of the infectious process.     

Role of glycosides as epithelial cell receptors for Candida albicans

The effect of various lectins and sugars on adhesion of five strains of Candida albicans to buccal and vaginal epithelial cells in vitro was investigated. Adhesion of C. albicans GDH 2346 was inhibited primarily by L-fucose and winged-pea lectin, whereas adhesion of strain GDH 2023 was inhibited by N-acetyl-D-glucosamine, or D-glucosamine, and wheat-germ agglutinin. Three other strains of C. albicans (MRL 3153, GRI 681 and GRI 682) gave results similar to those obtained with strain GDH 2346. Extracellular polymeric material (EP) isolated from strain GDH 2346 inhibited adhesion of strains MRL 3153, GRI 681 and GRI 682 by more than 50%, but that of strain GDH 2023 by only 30%. EP from strain GDH 2023 had little or no effect on the adhesion of any other yeast strain. Lectin-like proteins with affinities for L-fucose, N-acetyl-D-glucosamine and D-mannose were detected in EP from all five strains in different amounts. These results indicate that there are at least two types of adhesion mechanism and that glycosides containing L-fucose or N-acetyl-D-glucosamine can function as epithelial cell receptors for C. albicans.     

Selection and characterization of acriflavine-induced mutants of Candida albicans

Acriflavine-treated cells of C. albicans plated on a medium containing glucose as the principal carbon source gave rise to numerous colonies, most of which grew when replica-plated onto a similar medium containing sodium acetate substituted for glucose. Of the small fraction of colonies from the glucose medium which failed to replicate, some were found to be true petites, deficient for cytochromes a and b; others possessed complete cytochrome spectra, like those of their wild-type parents, but, nevertheless, respired at reduced rates on both fermentable and non-fermentable substrates. The role of the conventional cytochrome system in a wild-type culture was indicated by the strong inhibition of its respiration by cyanide, azide and antimycin A.     

Role of cell surface hydrophobicity in Candida albicans biofilm

Overall cell surface hydrophobicity (CSH) is predicted to play an important role during biofilm formation in Candida albicans but is the result of many expressed proteins. This study compares the CSH status and CSH1 gene expression in C. albicans planktonic cells, sessile biofilm, and dispersal cells. Greater percentages of hydrophobic cells were found in non-adhered (1.5 h) and dispersal forms (24 or 48 h) (41.34±4.17% and 39.52±7.45%, respectively), compared with overnight planktonic cultures (21.69±3.60%). Results from quantitative real-time PCR confirmed greater up-regulation of the CSH1 gene in sessile biofilm compared with both planktonic culture and dispersal cells. Up-regulation was also greater in dispersal cells compared with planktonic culture. The markedly increased CSH found both in C. albicans biofilm, and in cells released during biofilm formation could provide an advantage to dispersing cells building new biofilm.