Metabolic Adaptation of Isocitrate Lyase in the Yeast Pathogen Candida albicans

The ICL1 gene, which encodes the glyoxylate cycle enzyme isocitrate lyase (Icl1), is required for the growth of Candida albicans on non-fermentable carbon sources and for this yeast to be virulent. The aim of this study is to test the stability of the Icl1 enzyme in response to glucose. Glucose was found to trigger the degradation of the ICL1 but the CaIcl1 was not destabilized by glucose. When CaIcl1 was expressed in Saccharomycess cerevisiae, it was not degraded in response to glucose, suggesting that CaIcl1 has lost the molecular signal that triggers destabilization in response to glucose. However, when ScIcl1 was expressed in C. albicans it was rapidly degraded in response to glucose indicating that C. albicans has retained the molecular apparatus for glucose-accelerated degradation of target proteins. ScIcl1 degradation was slowed in Caubi4/ubi4 in which ubiquitin-mediated protein turnover is reduced. Furthermore, the addition of putative ubiquitination site to the carboxyl-terminus of CaIcl1 led to the glucose-accelerated degradation of this protein. C. albicans has retained the apparatus for ubiquitin-mediated degradation of target protein in response to glucose. However, CaIcl1 has lost the Ubi-site that mediate glucose accelerated protein degradation, thereby allowing C. albicans to simultaneously assimilate alternative carbon sources and glucose

Carbon Sources Attribute to Pathogenicity in Candida albicans

This topic was to examine the impact of galactose or fructose upon the assimilation of secondary carbon sources by Candida albicans. C. albicans ICL1 gene is repressed upon addition of 2% galactose or fructose to lactate- and oleic acid-grown cells. Further studies on CaFOX2, CaFBP1 and CaMLS1 transcripts in response to galactose or fructose on assimilation of lactate and oleic acid resulted in repression of these genes. The CaICL1 gene, which encode the glyoxylate cycles enzymes isocitrate lyase are required for growth on non-fermentable carbon sources. However, the enzyme CaIcl1 was not destabilized by galactose, but was degraded in response to fructose. In contrast, S. cerevisiae Icl1 has retained the molecular apparatus of protein degradation in response to either galactose or fructose. Screening of ubiquitination site by http://www.ubpred.org/ showed that C. albicans lacks ubiquitination site in gluconeogenic and glyoxylate cycles enzymes as compare to S. cerevisiae. Addition of a putative S. cerevisiae ubiquitination site carboxy terminus of CaIcl1 led to galactose- accelerated degradation of this protein in C. albicans cell via a ubiquitin-dependent process. In the other hand, CaIcl prior to addition of ubiquitination site was degraded upon exposure to fructose; addition of S. cerevisiae ubiquitination site to CaIcl1 further increased the speed of protein degradation

Effects of different mycotoxins on humans, cell genome and their involvement in cancer (Review)

The chemical nature of most of the mycotoxins makes them highly liposoluble compounds that can be absorbed from the site of exposure such as from the gastrointestinal and respiratory tract to the blood stream where it can be dissimilated throughout the body and reach different organs such as the liver and kidneys. Mycotoxins have a strong tendency and ability to penetrate the human and animal cells and reach the cellular genome where it causes a major mutagenic change in the nucleotide sequence which leads to strong and permanent defects in the genome. This defect will eventually be transcribed, translated and lead to the development of cancer. In this review, the chemical and physical nature of mycotoxins, the action of mycotoxins on the cellular genome and its effect on humans, mycotoxins and their carcinogenicity and mycotoxins research gaps are discussed, and new research areas are suggested. The research review posed various questions. What are the different mycotoxins that can cause cancer, what is the role of mycotoxins in causing cancer and what types of cancers can be caused by mycotoxins? These questions have been selected due to the significant increase in the mycotoxin contamination and the cancer incidence rate in the contemporary world. By revealing and understanding the role of mycotoxins in developing cancer, measures to reduce the risks and incidents of cancer could be taken

Yeast infection and diabetes mellitus among pregnant mother in Malaysia

Background: Vaginal yeast infection refers to irritation of the vagina due to the presence of opportunistic yeast of the genus Candida (mostly Candida albicans). About 75% of women will have at least one episode of vaginal yeast infection during their lifetime. Several studies have shown that pregnancy and uncontrolled diabetes increase the infection risk. Reproductive hormone fluctuations during pregnancy and elevated glucose levels characteristic of diabetes provide the carbon needed for Candida overgrowth and infection. The goal of this study was to determine the prevalence of vaginal yeast infection among pregnant women with and without diabetes. Methods: This was a case-control study using cases reports from Kepala Batas Health Clinic,Penang State,Malaysia from 2006 to 2012. In total,740 pregnant ladies were chosen as sample of which 370 were diabetic and 370 were non-diabetic cases. Results: No relationship between diabetes and the occurrence of vaginal yeast infection in pregnant women was detected, and there was no significant association between infection and age group, race or education level. Conclusion: In conclusion, within radius of this study, vaginal yeast infection can occur randomly in pregnant women

In vitro modulation of probiotic bacteria on the biofilm of Candida glabrata

A conspicuous new concept of pathogens living as the microbial societies in the human host rather than free planktonic cells has raised considerable concerns among scientists and clinicians. Fungal biofilms are communities of cells that possess distinct characteristic such as increased resistance to the immune defence and antimycotic agents in comparison to their planktonic cells counterpart. Therefore, inhibition of the biofilm may represent a new paradigm for antifungal development. In this study, we aim to evaluate the in vitro modulation of vulvovaginal candidiasis (VVC)-causing Candida glabrata biofilms using probiotic lactobacilli strains. Probiotic Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 were shown to have completely inhibited C. glabrata biofilms and the results were corroborated by scanning electron microscopy (SEM), which revealed scanty structures of the mixed biofilms of C. glabrata and probiotic lactobacilli strains. In addition, biofilm-related C. glabrata genes EPA6 and YAK1 were downregulated in response to the probiotic lactobacilli challenges. The present study suggested that probiotic L. rhamnosus GR-1 and L. reuteri RC-14 strains inhibited C. glabrata biofilm by partially impeding the adherence of yeast cells and the effect might be contributed by the secretory compounds produced by these probiotic lactobacilli strains. Further investigations are required to examine and identify the biofilm inhibitory compounds and the mechanism of probiotic actions of these lactobacilli strains

Physiologically Relevant Alternative Carbon Sources Modulate Biofilm Formation, Cell Wall Architecture and the Stress and Antifungal Resistance of Candida glabrata

Acknowledgments: This study was funded by Fundamental Research Grant Scheme (FRGS) from Ministry of Education (MOE), Malaysia (Grant number: 01-01-14-1456FR). S.Y.C. is a recipient of the MyBrain 15 Scholarship from MOE, Malaysia. AB was supported by the UK Medical Research Council (www.mrc.ac.uk: MR/M026663/1), the Medical Research Council Centre for Medical Mycology (MR/N006364/1), the Wellcome Trust (www.wellcome.ac.uk: 097377), and the European Commission (FunHoMic: H2020-MSCA-ITN-2018-812969)Peer reviewedPublisher PD

Glyoxylate cycle gene ICL1 is essential for the metabolic flexibility and virulence of Candida glabrata

We would like to acknowledge Professor Karl Kuchler from Medical University of Vienna for the kind gifts of C. glabrata strains used in this study. This study was funded by Fundamental Research Grant Scheme (FRGS) from Ministry of Education (MOE), Malaysia (Grant number: 01-01-14-1456FR). S.Y. is a recipient of the MyBrain 15 Scholarship from MOE, Malaysia. A.B. was supported by the Medical Research Council Centre for Medical Mycology at the University of Aberdeen (MR/N006364/1), by a programme grant from the UK Medical Research Council (MR/M026663/1), by a Strategic Award from the Wellcome Trust (097377) and by a grant from the UK Biotechnology and Biological Sciences Research Council (BB/P020119/1).Peer reviewedPublisher PD

Growth, biofilm formation, antifungal susceptibility and oxidative stress resistance of Candida glabrata are affected by different glucose concentrations

Glucose is an important fuel source to support many living organisms. Its importance in the physiological fitness and pathogenicity of Candida glabrata, an emerging human fungal pathogen has not been extensively studied. The present study aimed to investigate the effects of glucose on the growth, biofilm formation, antifungal susceptibility and oxidative stress resistance of C. glabrata. In addition, its effect on the expression of a putative high affinity glucose sensor gene, SNF3 was also investigated. Glucose concentrations were found to exert effects on the physiological responses of C. glabrata. The growth rate of the species correlated positively to the amount of glucose. In addition, low glucose environments were found to induce C. glabrata to form biofilm and resist amphotericin B. Conversely, high glucose environments promoted oxidative stress resistance of C. glabrata. The expression of CgSNF3 was found to be significantly up-regulated in low glucose environments. The expression of SNF3 gene in clinical isolates was found to be higher compared to ATCC laboratory strains in low glucose concentrations, which may explain the better survivability of clinical isolates in the low glucose environment. These observations demonstrated the impact of glucose in directing the physiology and virulence fitness of C. glabrata through the possible modulation by SNF3 as a glucose sensor, which in turn aids the species to adapt, survive and thrive in hostile host environment

Tualang honey improves human corneal epithelial progenitor cell migration and cellular resistance to oxidative stress in vitro

Stem cells with enhanced resistance to oxidative stress after in vitro expansion have been shown to have improved engraftment and regenerative capacities. Such cells can be generated by preconditioning them with exposure to an antioxidant. In this study we evaluated the effects of Tualang honey (TH), an antioxidant-containing honey, on human corneal epithelial progenitor (HCEP) cells in culture. Cytotoxicity, gene expression, migration, and cellular resistance to oxidative stress were evaluated. Immunofluorescence staining revealed that HCEP cells were holoclonal and expressed epithelial stem cell marker p63 without corneal cytokeratin 3. Cell viability remained unchanged after cells were cultured with 0.004, 0.04, and 0.4% TH in the medium, but it was significantly reduced when the concentration was increased to 3.33%. Cell migration, tested using scratch migration assay, was significantly enhanced when cells were cultured with TH at 0.04% and 0.4%. We also found that TH has hydrogen peroxide (H2O2) scavenging ability, although a trace level of H2O2 was detected in the honey in its native form. Preconditioning HCEP cells with 0.4% TH for 48 h showed better survival following H2O2-induced oxidative stress at 50 µM than untreated group, with a significantly lower number of dead cells (15.3 ± 0.4%) were observed compared to the untreated population (20.5 ± 0.9%, p<0.01). Both TH and ascorbic acid improved HCEP viability following induction of 100 µM H2O2, but the benefit was greater with TH treatment than with ascorbic acid. However, no significant advantage was demonstrated using 5-hydroxymethyl-2-furancarboxaldehyde, a compound that was found abundant in TH using GC/MS analysis. This suggests that the cellular anti-oxidative capacity in HCEP cells was augmented by native TH and was attributed to its antioxidant properties. In conclusion, TH possesses antioxidant properties and can improve cell migration and cellular resistance to oxidative stress in HCEP cells in vitro

Metabolic adaptation via regulated enzyme degradation in the pathogenic yeast Candida albicans

The virulence of Candida albicans is dependent upon fitness attributes as well as virulence factors. These attributes include robust stress responses and metabolic flexibility. The assimilation of carbon sources is important for growth and essential for the establishment of infections by C. albicans. Previous studies showed that the C. albicans ICL1 genes, which encode the glyoxylate cycle enzymes isocitratelyase are required for growth on non-fermentable carbon sources such as lactate and oleic acid and were repressed by 2% glucose. In contrast to S. cerevsiae, the enzyme CaIcl1 was not destabilised by glucose, resulting with its metabolite remaining at high levels. Further glucose addition has caused CaIcl1 to lose its signal and mechanisms that trigger destabilization in response to glucose. Another purpose of this study was to test the stability of the Icl1 enzyme in response to the dietary sugars, fructose, and galactose. In the present study, the ICL1 mRNAs expression was quantified using Quantitative Real Time PCR, whereby the stability of protein was measured and quantified using Western blot and phosphoimager, and the replacing and cloning of ICL1 ORF by gene recombination and ubiquitin binding was conducted via co-immuno-precipitation. Following an analogous experimental approach, the analysis was repeated using S. cerevisiaeas a control. Both galactose and fructose were found to trigger the degradation of the ICL1 transcript in C. albicans. The Icl1 enzyme was stable following galactose addition but was degraded in response to fructose. C. albicans Icl1 (CaIcl1) was also subjected to fructose-accelerated degradation when expressed in S. cerevisiae, indicating that, although it lacks a ubiquitination site, CaIcl1 is sensitive to fructose-accelerated protein degradation. The addition of an ubiquitination site to CaIcl1 resulted in this enzyme becoming sensitive to galactose-accelerated degradation and increases its rate of degradation in the presence of fructose. It can be concluded that ubiquitin-independent pathways of fructose-accelerated enzyme degradation exist in C. albicans