Identification and functional characterization of a lipid droplet protein CtLDP1 from an oleaginous yeast Candida tropicalis SY005.

Proteins residing in lipid droplets (LDs) of organisms exhibit diverse physiological roles. Since the LD proteins of yeasts are largely unexplored, we have identified a putative LD protein gene, CtLDP1 in the oleaginous yeast Candida tropicalis SY005 and characterized its function. The increased lipid accumulation in SY005 could be correlated with enhanced (~2.67-fold) expression of the CtLDP1 after low-nitrogen stress. The N-terminal transmembrane domain similar to perilipin proteins and the amphipathic α-helices predicted in silico, presumably aid in targeting the CtLDP1 to LD membranes. Heterologous expression of CtLDP1-mCherry fusion in Saccharomyces cerevisiae revealed localization in LDs, yet the expression of CtLDP1 did not show significant effect on LD formation in transformed cells. Molecular docking showed favourable interactions of the protein with sterol class of molecules, but not with triacylglycerol (TAG); and this was further experimentally verified by co-localization of the mCherry-tagged protein in TAG-deficient (but steryl ester containing) LDs. While oleic acid supplementation caused coalescence of LDs into supersized ones (average diameter = 1.19 ± 0.12 µm; n = 160), this effect was suppressed due to CtLDP1 expression, and the cells mostly exhibited numerous smaller LDs (average diameter = 0.46 ± 0.05 µm; n = 160). Moreover, CtLDP1 expression in pet10Δ knockout strain of S. cerevisiae restored multiple LD formation, indicating functional complementation of the protein. Overall, this study documents functional characterization of an LD-stabilizing protein from an oleaginous strain of Candida genus for the first time, and provides insights on the characteristics of LD proteins in oleaginous yeasts for future metabolic engineering.

ClCPI, a cysteine protease inhibitor purified from Cassia leiandra seeds has antifungal activity against Candida tropicalis by inducing disruption of the cell surface.

Infections caused by Candida tropicalis have increased significantly worldwide in parallel with resistance to antifungal drugs. To overcome resistance novel drugs have to be discovered. The objective of this work was to purify and characterize a cysteine protease inhibitor from the seeds of the Amazon rainforest tree Cassia leiandra and test its inhibitory effect against C. tropicalis growth. The inhibitor, named ClCPI, was purified after ion exchange and affinity chromatography followed by ultrafiltration. ClCPI is composed of a single polypeptide chain and is not a glycoprotein. The molecular mass determined by SDS-PAGE in the absence or presence of ß-mercaptoethanol and ESI-MS were 16.63 kDa and 18.362 kDa, respectively. ClCPI was stable in the pH range of 7.0-9.0 and thermostable up to 60 °C for 20 min. ClCPI inhibited cysteine proteases, but not trypsin, chymotrypsin neither alpha-amylase. Inhibition of papain was uncompetitive with a Ki of 4.1 × 10-7 M and IC50 of 8.5 × 10-7 M. ClCPI at 2.6 × 10-6 M reduced 50% C. tropicalis growth. ClCPI induced damages and morphological alterations in C. tropicalis cell surface, which led to death. These results suggest that ClCPI have great potential for the development of an antifungal drug against C. tropicalis.

CGA-N9, an antimicrobial peptide derived from chromogranin A: direct cell penetration of and endocytosis by Candida tropicalis.

CGA-N9 is a peptide derived from the N-terminus of human chromogranin A comprising amino acids 47-55. Minimum inhibitory concentration (MIC) assays showed that CGA-N9 had antimicrobial activity and exhibited time-dependent inhibition activity against Candida tropicalis, with high safety in human red blood cells (HRBCs) and mouse brain microvascular endothelial cells (bEnd.3). According to the results of transmission electron microscopy (TEM), flow cytometry and confocal microscopy, CGA-N9 accumulated in cells without destroying the integrity of the cell membrane; the peptide was initially localized to the cell membrane and subsequently internalized into the cytosol. An investigation of the cellular internalization mechanism revealed that most CGA-N9 molecules entered the yeast cells, even at 4°C and in the presence of sodium azide (NaN3), both of which block all energy-dependent transport mechanisms. In addition, peptide internalization was affected by the endocytic inhibitors 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), cytochalasin D (CyD) and heparin; chlorpromazine (CPZ) also had some effect on CGA-N9 internalization. Similar results were obtained in the MIC assays, whereby the anticandidal activity of CGA-N9 was blocked to different degrees in the presence of EIPA, CyD, heparin or CPZ. Therefore, most CGA-N9 passes through the C. tropicalis cell membrane via direct cell penetration, whereas the remainder enters through macropinocytosis and sulfate proteoglycan-mediated endocytosis, with a slight contribution from clathrin-mediated endocytosis.

Antifungal activity of spider venom-derived peptide lycosin-I against Candida tropicalis.

Candida species are a major cause of human mucosal and deep tissue fungal infections, but few antifungal treatments are available. Here, we showed that lycosin-I, a peptide isolated from venom of the spider Lycosa singoriensis, acted as a potent antifungal inhibitor against Candida species. The MIC50 values of lycosin-I reached 8 µg/mL to treat fluconazole-susceptible and fluconazole-resistant C. tropicalis isolates. Time-kill kinetics assays revealed that after a 2-hour exposure, lycosin-I reduced colony-forming units/mL in fluconazole-susceptible and fluconazole-resistant C. tropicalis isolates approximately 70%. Furthermore, salinity tolerance assays suggested that even in the presence of Mg2+, lycosin-I maintained its potent antifungal ability at a high concentration. When the concentration of lycosin-I was increased from 1 × MIC to 8 × MIC, a significant decrease of the biofilm metabolic activity was observed in both fluconazole-susceptible and fluconazole-resistant C. tropicalis isolates. Moreover, the biofilm inhibitory concentration 50 (BIC50) and the biofilm eradicating concentration 50 (BEC50) were approximately 32 µg/mL and 128 µg/mL, respectively. Confocal laser scanning microscopy showed the localization of CY5-labeled lycosin-I mainly in the cell cytoplasm, and lycosin-I was likely to be localized in the cytoplasm after its transportation across the cell wall and membrane. Overall, our work shows that lycosin-I is a potent antifungal agent with a high efficacy, a high salinity tolerance, and potent anti-biofilm properties.

Mechanistic investigations in ultrasound-assisted xylitol fermentation.

This study has investigated ultrasound-assisted xylitol production through fermentation of dilute acid (pentose-rich) hydrolysate of sugarcane bagasse using free cells of Candida tropicalis. Sonication of fermentation mixture at optimum conditions was carried out in ultrasound bath (37 kHz and 10% duty cycle). Time profiles of substrate and product in control (mechanical shaking) and test (mechanical shaking + sonication) fermentations were fitted to kinetic model using Genetic Algorithm (GA) optimization. Max. xylitol yield of 0.56 g/g and 0.61 g/g of xylose was achieved in control and test fermentations, respectively. The biomass yield also increased marginally (∼17%) with sonication. However, kinetics of fermentation increased drastically (2.5×) with sonication with 2× rise in xylose uptake and utilization by the cells. With comparative analysis of kinetic parameters in control and test experiments, this result was attributed to enhanced permeability of cell membrane that allowed faster diffusion of nutrients, substrates and products across cell membrane, higher enzyme-substrate affinity, dilution of toxic components and reduced inhibition of intracellular enzymes by substrate.

Comprehending the influence of critical cultivation parameters on the oleaginous behaviour of potent rotten fruit yeast isolates.

AIMS: Oleaginous yeasts were isolated from five different rotten fruits and their oleaginous behaviour was characterized with varying carbon source and concentration (C/N) to identify their possible future applicabilities. METHODS AND RESULTS: Sixteen yeasts were isolated, those accumulating around 20% of their cell dry weights as lipids were screened and identified as Candida tropicalis and Pichia kudriavzevii. Among glucose, maltose and sucrose, glucose was found favourable carbon source in terms of biomass yield and lipid content. Carbon concentration corresponding to C/N ratio 100/2 (C. tropicalis) and 120/2 (P. kudriavzevii) exhibited highest lipid contents-81·2 and 75·7%-and lipid yields-1·1 and 3 g l-1 , respectively. Lipids contained 16-28 types of triacylglycerols, and major fatty acids detected were caprylic, caparate, lauric, stearic palmitic, oleic, linoleic, aracidic and erucic acid with caprylic acid as predominant one. Fatty acid profile also witnessed variations with changing C/N. CONCLUSIONS: Noteworthy lipid contents were achieved in the two isolates higher than any existing reports on them. Pichia kudriavzevii exhibited reasonable overall lipid yield extending the opportunity of improvement upon changing the cultivation conditions. The lipids contained a range of fatty acids with a predominance of caprylic acid having unequivocal biotechnological importance. SIGNIFICANCE AND IMPACT OF THE STUDY: Two potent oleaginous yeast isolates were studied, and this is the only successive report describing oleaginous behaviour of P. kudriavzevii. The cultivation parameters such as C source, concentration and C/N ratio which critically influence the oleaginous behaviour, lipid content, yield and composition have been accessed so as to provide comprehensive understanding on single cell oil production from these isolates. Study progressively contributes to current and upcoming researches in microbial oils and the characteristic fatty acid, and TAG profile provides important leads for their putative applicabilities.

In vitro effects of promethazine on cell morphology and structure and mitochondrial activity of azole-resistant Candida tropicalis.

The aim of this study was to evaluate the effect of promethazine on the antifungal minimum inhibitory concentrations against planktonic cells and mature biofilms of Candida tropicalis, as well as investigate its potential mechanisms of cell damage against this yeast species. Three C. tropicalis isolates (two azole-resistant and one azole-susceptible) were evaluated for their planktonic and biofilm susceptibility to promethazine alone and in combination with itraconazole, fluconazole, voriconazole, amphotericin B, and caspofungin. The antifungal activity of promethazine against C. tropicalis was investigated by performing time-kill curve assays and assessing rhodamine 6G efflux, cell size/granularity, membrane integrity, and mitochondrial transmembrane potential, through flow cytometry. Promethazine showed antifungal activity against planktonic cells and biofilms at concentrations of 64 and 128 µg/ml, respectively. The addition of two subinhibitory concentrations of promethazine reduced the antifungal MICs for all tested azole drugs against planktonic growth, reversing the resistance phenotype to all azoles. Promethazine decreased the efflux of rhodamine 6G in an azole-resistant strain. Moreover, promethazine decreased cell size/granularity and caused membrane damage, and mitochondrial membrane depolarization. In conclusion, promethazine presented synergy with azole antifungals against resistant C. tropicalis and exhibited in vitro cytotoxicity against C. tropicalis, altering cell size/granularity, membrane integrity, and mitochondrial function, demonstrating potential mechanisms of cell damage against this yeast species.

γ-irradiation from radiotherapy improves the virulence potential of Candida tropicalis.

AIM: To evaluate if radiation used in radiotherapy can cause changes in the virulence potential of Candida tropicalis ATCC 750. MATERIALS & METHODS: C. tropicalis was exposed in vitro to identical dose and scheme of irradiation would be used in patients with head and neck cancer. Some virulence parameters were analyzed before and after irradiation. RESULTS: Colony morphologies were irreversibly affected by irradiation. Increase in growth rate, filamentation, adhesion on cell lines and phagocytosis process were also observed. Overall the irradiated C. tropicalis cells became more efficient at causing systemic infection in mice. CONCLUSION: γ-radiation induced important changes in C. tropicalis increasing its virulence profile, which could directly affect the relationship between yeasts and hosts.

Ultrasonic irradiation of low intensity with a mode of sweeping frequency enhances the membrane permeability and cell growth rate of Candida tropicalis.

Here we report the enhancement of both cellular permeability and cell growth rate of Candida tropicalis after treatment with the ultrasonic irradiation of low intensity using a mode of sweeping frequency (UILS) generated by a self-developed ultrasonic device in our lab. After the ultrasonic treatment, remarkable biomass enhancement of the yeast was observed; the hyphae became significantly longer; the seeped cellular protein and nucleic acid from the yeast increased and the cellular Ca2+ content became lower. Illumina transcriptome sequencing showed that the ultrasonic treatment affected the expression of genes involved in diverse cellular components, biological processes and molecular functions. RT-PCR and Western blotting further confirmed the up-/down-regulation of genes in the ultrasound-treated yeasts. The optimal conditions of the ultrasonic treatment for the maximum biomass addition were determined as follows: the yeast was treated for 1h at the mid logarithmic phase, the frequency was 28±2kHz and the power density was 120W/L. Under these conditions, the Candida tropicalis biomass increased by 142.5% compared with the untreated yeast.

Antifungal Activity of Condensed Tannins from Stryphnodendron adstringens: Effect on Candida tropicalis Growth and Adhesion Properties.

Candida species are some of the most common causes of fungal infection worldwide. The limited efficacy of clinically available antifungals warrants the search for new compounds for treating candidiasis. This study evaluated the effect of condensed tannin-rich fraction (F2 fraction) of Stryphnodendron adstringens on in vitro and in vivo growth of Candida tropicalis, and on yeast adhesion properties. F2 exhibited a fungistatic effect with the minimum inhibitory concentration ranging from 0.5 to 8.0 µg/mL. A significant reduction in biofilm mass was observed after either pretreatment of planktonic cells for 2 h (mean reduction of 46.31±8.17%) or incubation during biofilm formation (mean reduction of 28.44±13.38%) with 4x MIC of F2. Prior exposure of planktonic cells to this F2 concentration also significantly decreased yeast adherence on HEp-2 cells (mean reduction of 43.13±14.29%), cell surface hydrophobicity (mean reduction of 25.89±10.49%) and mRNA levels of the genes ALST1-3 (2.9-, 1.8- and 1.8-fold decrease, respectively). Tenebrio molitor larvae, which are susceptible to C. tropicalis infection, were used for in vivo testing. Treatment with 128 and 256 µg/mL F2 significantly increased the survival of infected larvae. These results indicate a combined effect of F2 on inhibition of yeast growth and interference in yeast adhesion, which may contribute to the suppression of infection caused by C. tropicalis, thus reinforcing the potential of the condensed tannins from S. adstringens for the development of novel antifungal agents.

Aerobic decolorization and degradation of Acid Orange G (AOG) by suspended growing cells and immobilized cells of a yeast strain Candida tropicalis TL-F1.

In this study, aerobic decolorization and degradation of azo dye Acid Orange G (AOG) by both suspended growing cells and immobilized cells of a yeast strain Candida tropicalis TL-F1 were studied. The effects of different parameters on decolorization of AOG by both growing suspended and immobilized strain TL-F1 were investigated. Furthermore, a possible decolorization mechanism of AOG was proposed through analyzing metabolic intermediates using UV-vis and high-performance liquid chromatography-mass spectrometry (HPLC-MS) methods. Strain TL-F1 could decolorize AOG in both liquid and solid mediums through degradation. The optimal conditions for decolorization with suspended growing cells of strain TL-F1 were as follows: 6-10 g/L sucrose, 5-7 g/L urea, ≥6 % (v/v) inoculation size, ≥160 rpm, 35-40 °C, and pH 5.0-6.0; and those for immobilized cells, the conditions were as follows: 4-6 g/L glucose, 0.2-0.4 g/L urea, 6-10 g/L (wet cell pellets) inoculation size, ≥160 rpm, 35-40 °C, and pH 5.0-7.0. Results of UV-vis scanning spectra suggested that AOG was decolorized through biodegradation, and the possible pathway was proposed through the results of HPLC-MS analysis and related literature. This is a systematic research on aerobic decolorization and degradation of AOG by both suspended and immobilized cells of a C. tropicalis strain.

The antibiotic and membrane-damaging activities of cellobiose lipids and sophorose lipids.

Antibiotic activity was compared for Cryptococcus humicola cellobiose lipids, the mixture of 2,3,4-О-triacetyl-ß-D-glucopyranosyl-(1→4)-(6-О-acetyl-ß-D-glucopyranosyl-(1→16)-2,16-dihydroxyhexodecanoic acid and 2,3,4-О-triacetyl-ß-D-glucopyranosyl-(1→4)-(6-О-acetyl-ß-D-glucopyranosyl-(1→16)-2,17,18-trihydroxyoctotodecanoic acid, and the commercial sophorose lipid mixture of a mono-acetylated acidic sophorose lipid and a di-acetylated acidic sophorose lipid, both containing the C18:1 fatty acid residue. The MIC values of cellobiose lipids were 0.005 and 0.04 mg/mL for Filobasidiella neoformans and Candida tropicalis, respectively. The MIC values of sophorose lipids were 1 and 15 mg/mL for F. neoformans and C. tropicalis, respectively. MIC values for some bacteria were in the range of 10-30 mg/mL for both glycolipid preparations. Both sophorose lipids and cellobiose lipids displayed a membrane-damaging activity against F. neoformans. The treatment with these glycolipids reduces the content of ATP in the cells of test cultures and results in their staining with ethidium bromide.

Parasexuality and ploidy change in Candida tropicalis.

Candida species exhibit a variety of ploidy states and modes of sexual reproduction. Most species possess the requisite genes for sexual reproduction, recombination, and meiosis, yet only a few have been reported to undergo a complete sexual cycle including mating and sporulation. Candida albicans, the most studied Candida species and a prevalent human fungal pathogen, completes its sexual cycle via a parasexual process of concerted chromosome loss rather than a conventional meiosis. In this study, we examine ploidy changes in Candida tropicalis, a closely related species to C. albicans that was recently revealed to undergo sexual mating. C. tropicalis diploid cells mate to form tetraploid cells, and we show that these can be induced to undergo chromosome loss to regenerate diploid forms by growth on sorbose medium. The diploid products are themselves mating competent, thereby establishing a parasexual cycle in this species for the first time. Extended incubation (>120 generations) of C. tropicalis tetraploid cells under rich culture conditions also resulted in instability of the tetraploid form and a gradual reduction in ploidy back to the diploid state. The fitness levels of C. tropicalis diploid and tetraploid cells were compared, and diploid cells exhibited increased fitness relative to tetraploid cells in vitro, despite diploid and tetraploid cells having similar doubling times. Collectively, these experiments demonstrate distinct pathways by which a parasexual cycle can occur in C. tropicalis and indicate that nonmeiotic mechanisms drive ploidy changes in this prevalent human pathogen.

Determination of biofilm production by Candida tropicalis isolated from hospitalized patients and its relation to cellular surface hydrophobicity, plastic adherence and filamentation ability.

Candida tropicalis is an emerging virulent species. The aim of this study is to determine the biofilm-forming ability of 29 strains of C. tropicalis isolated from inpatients, and to examine its relation with other virulence factors such as cellular surface hydrophobicity (CSH), immediate (15 min, IA) and late (24 h, LA) plastic adherence and filamentation ability. The study was performed in parallel using two incubation temperatures - 37 and 22 °C - to determine the effect of growth temperature variations on these pathogenic attributes of C. tropicalis. Biofilm formation (BF) was measured by optical density (OD) and by XTT reduction (XTT); Slime index (SI), which includes growth as a correction factor in BF, was calculated in both methods. All strains were hydrophobic and adherent - at 15 min and 24 h - at both temperatures, with higher values for 22 °C; the adhered basal yeast layer appears to be necessary to achieve subsequent development of biofilm. Filamentation ability varied from 76.2% of strains at 37 °C to 26.6% at 22 °C. All C. tropicalis strains were biofilm producers, with similar results obtained using OD determination and XTT measurement to evaluation methods; SI is useful when good growth is not presented. BF at 37 °C was similar at 24 h and 96 h incubation; conversely, at 22 °C, the highest number of biofilm-producing strains was detected at 96 h. CSH is an important pathogenic factor which is involved in adherence, is influenced by the filamentation of yeast, and plays a critical role in BF.

Efecto combinado del aceite esencial de Cinnamomum zeylanicum blume y nistatina sobre cepas de Candida no-albicans / Combined effect of Cinnamomum zeylanicum blume essential oil and nystatin on strains of non-albicans Candida

Introduction: considering the emergence of resistant species of albicans and non-albicans Candida to agents therapeutically available as a result of the increased number of immunocompromised population and of the increasingly frequent use of prophylaxis and empirical treatment with antifungals, it's verified that there is a clear and emerging need to introduce new antimicrobials agents in the therapeutic arsenal. The purpose of this study was to evaluate the antifungal activity of essential oil of Cinnamomum zeylanicum Blume alone and combined with Nystatin on strains of C. tropicalis and C. krusei. Methods: this was an experimental research in laboratory. It was determined the Minimum Inhibitory Concentration, using the microdilution method, as well as the Fractional Inhibitory Concentration to determine the possible synergistic effects of the association. Strains of C. tropicalis ATCC 40147 and C. krusei ATCC 40042 were used in the tests. When assessed separately, C. zeylanicum essential oil and Nystatin presented Minimum Inhibitory Concentration of 312,5 µg/mL and 64 µg/mL, respectively, on both tested strains. Results: When combined, were found Minimum Inhibitory Concentration of 39 µg/mL and 32 µg/mL for the essential oil and for Nystatin, respectively. The Fractional Inhibitory Concentration value was 0,6024 for both tested strains, indicating additivity of the inhibitory effect on fungal growth. Conclusions: the results indicate that C. zeylanicum essential oil has antifungal activity against the strains of non-albicans Candida evaluated and that its association with Nystatin potentiates this effect(AU)

Introducción: es necesaria la introducción de nuevos agentes antimicrobianos por el surgimiento de especies de Candida albicans y no albicans resistentes a los agentes terapéuticos disponibles .El objetivo del estudio fue evaluar la actividad antifúngica del aceite esencial de Cinnamomum zeylanicum Blume aislado y asociado con nistatina sobre cepas Candida tropicalis y Candida krusei. Métodos: se realizó una investigación experimental de laboratorio. La concentración mínima inhibitoria fue determinada utilizando el método de microdilución, y la concentración inhibitoria fraccionada se usó para determinar los posibles efectos sinérgicos de la asociación. Para las pruebas fueron utilizadas las cepas de C. tropicalis ATCC 40147 y C. krusei ATCC 40042. Se usaron el aceite esencial de C. zeylanicum y nistatina. Cuando fueron evaluados por separado presentaron la concentración mínima inhibitoria de 312,5 µg/mL y de 64 µg/mL, respectivamente, sobre ambas cepas ensayadas. Resultados: una vez asociados, la concentración mínima inhibitoria fue de 39 µg/mL para el aceite esencial y de 32 µg/mL para la nistatina. El valor de la concentración inhibitoria fraccionada para ambas cepas probadas fue de 0,6024, lo que indica adicción del efecto inhibidor sobre el crecimiento de hongos. Conclusiones: los resultados indican que el aceite esencial de C. zeylanicum tiene actividad antifúngica frente a las cepas de Candida no albicans y que la asociación del mismo con la nistatina promueve la potenciación de este efecto(AU)

Aerobic decolorization and degradation of azo dyes by growing cells of a newly isolated yeast Candida tropicalis TL-F1.

The aim of this work was to investigate the decolorization and degradation of azo dyes by growing cells of a new yeast strain TL-F1 which was isolated from the sea mud. Strain TL-F1 was identified as Candida tropicalis on the basis of 28S rDNA analysis. Various azo dyes (20mg/L) were efficiently decolorized through aerobic degradation. Meantime, the effects of different parameters on both decolorization of Acid Brilliant Scarlet GR and growth of strain TL-F1 were investigated. Furthermore, possible degradation pathway of the dye GR was proposed through analysis of metabolic products using UV-Vis spectroscopy and HPLC-MS methods. As far as it is known, it is the first systematic research on a C. tropicalis strain which is capable of efficiently decolorizing various azo dyes under aerobic condition. This work provides a potentially useful microbial strain TL-F1 for treatment of azo dye contaminated wastewater.

Evaluation of corncob hemicellulosic hydrolysate for xylitol production by adapted strain of Candida tropicalis.

A maximum xylose extraction of 21.98 g/L was obtained in hydrolysate with a solid to liquid ratio of 1:8 (w/v) at 1% H(2)SO(4) and treated for 30 min. The optimized and treated corncob hemicellulosic hydrolysate medium supplemented with (g/L) yeast extract 5.0, KH(2)PO(4) 2.0, MgSO(4)·7H(2)O 0.3 and methanol 10 mL whose pH was adjusted to 4.5 acts as production medium. Under this condition; the adapted strain of C. tropicalis resulted in 1.22-fold increase in xylitol yield and 1.70-fold enhancement in volumetric productivity was obtained as compared to parent strain of C. tropicalis. On concentrating the hydrolysate under vacuum using rotavapor proves to be efficient in terms of improved xylitol yield and productivity over microwave assisted concentration using adapted strain of C. tropicalis. The immobilized cells of C. tropicalis resulted in more than 70% efficiency up to third cycle. The xylitol production could be scaled up to 10 L fermentor.

Xylitol production from corncob hydrolysate using polyurethane foam with immobilized Candida tropicalis.

Polyurethane foam (PUF) was used as a carrier for Candida tropicalis (C. tropicalis) in the multi-batches fermentation of xylitol from xylose-containing corncob hemicellulose hydrolysate. After washing and sterilization, PUF (density of 320 kgm(-3), specific surface area of 1.5-2.0 × 10(5) m(2) m(-3), average porosity of 95%, pore diameter of 0.03 mm and cubic length of 5mm) was mixed with the culture medium at appropriate proportion followed by the inoculation. The fermentation parameters such as initial cell concentration, PUF dosage, pH value and temperature were controlled to study the effects on xylitol fermentation. In the 21-day durability tests, the optimal xylitol yield and volumetric productivity reached to 71.2% and 2.10 gL(-1)h(-1) respectively. Moreover, the average xylitol yield and volumetric productivity were 66.3% and 1.90 gL(-1)h(-1) for ten batchwise operations. The current research demonstrated that the PUF immobilization could serve as an efficient method for improving the cells vitality and enzyme reactivity in the continuous operation of fermentation.

N-acetylglucosamine induces white-to-opaque switching and mating in Candida tropicalis, providing new insights into adaptation and fungal sexual evolution.

Pathogenic fungi are capable of switching between different phenotypes, each of which has a different biological advantage. In the most prevalent human fungal pathogen, Candida albicans, phenotypic transitions not only improve its adaptation to a continuously changing host microenvironment but also regulate sexual mating. In this report, we show that Candida tropicalis, another important human opportunistic pathogen, undergoes reversible and heritable phenotypic switching, referred to as the "white-opaque" transition. Here we show that N-acetylglucosamine (GlcNAc), an inducer of white-to-opaque switching in C. albicans, promotes opaque-cell formation and mating and also inhibits filamentation in a number of natural C. tropicalis strains. Our results suggest that host chemical signals may facilitate this phenotypic switching and mating of C. tropicalis, which had been previously thought to reproduce asexually. Overexpression of the C. tropicalis WOR1 gene in C. albicans induces opaque-cell formation. Additionally, an intermediate phase between white and opaque was observed in C. tropicalis, indicating that the switching could be tristable.

Interdigital ulcer: an unusual presentation of Candida infection.

Interdigital ulcer is an exceptionally rare condition while erosio interdigitalis blastomycetica is common for candidiasis. Four Chinese patients with Candida interdigital ulcers were reported. The exudates were examined directly and cultured for fungi. Skin biopsies were stained with haematoxylin-eosin and periodic acid Schiff. There were a man and three women (age range: 34-56 years) who presented with 1- to 3-month history of chronic cutaneous ulcer on the interdigital web of hand or foot. The lesions were located on hand for one woman, and on the left foot for the rest. The patients had poor response to the previous treatment of topical steroids and oral antimicrobials. Candida albicans was isolated from a man and two women, Candida tropicalis from another woman. Biopsy specimens revealed yeast and mycelium as well as inflammatory infiltrate in necrotic tissue in two patients; only inflammatory cells in the other two. The patients had complete remission with oral itraconazole and topical bifonazole cream therapy for 3- to 5-week. Candida species may cause interdigital ulcer on hand or foot. Oral itraconazole and topical bifonazole may be an optional therapy for such an ulcer.