Transcriptional Regulation of Carbohydrate Metabolism in the Human Pathogen Candida albicans

Glycolysis is a metabolic pathway that is central to the assimilation of carbon for either respiration or fermentation and therefore is critical for the growth of all organisms. Consequently, glycolytic transcriptional regulation is important for the metabolic flexibility of pathogens in their attempts to colonize diverse niches. We investigated the transcriptional control of carbohydrate metabolism in the human fungal pathogen Candida albicans and identified two factors, Tye7p and Gal4p, as key regulators of glycolysis. When respiration was inhibited or oxygen was limited, a gal4tye7 C. albicans strain showed a severe growth defect when cultured on glucose, fructose or mannose as carbon sources. The gal4tye7 strain displayed attenuated virulence in both Galleria and mouse models as well, supporting the connection between pathogenicity and metabolism. Chromatin immunoprecipitation coupled with microarray analysis (ChIP-CHIP) and transcription profiling revealed that Tye7p bound the promoter sequences of the glycolytic genes and activated their expression during growth on either fermentable or non-fermentable carbon sources. Gal4p also bound the glycolytic promoter sequences and activated the genes although to a lesser extent than Tye7p. Intriguingly, binding and activation by Gal4p was carbon source-dependent and much stronger during growth on media containing fermentable sugars than on glycerol. Furthermore, Tye7p and Gal4p were responsible for the complete induction of the glycolytic genes under hypoxic growth conditions. Tye7p and Gal4p also regulated unique sets of carbohydrate metabolic genes; Tye7p bound and activated genes involved in trehalose, glycogen, and glycerol metabolism, while Gal4p regulated the pyruvate dehydrogenase complex. This suggests that Tye7p represents the key transcriptional regulator of carbohydrate metabolism in C. albicans and Gal4p provides a carbon source-dependent fine-tuning of gene expression while regulating the metabolic flux between respiration and fermentation pathways

Reverse genetics in Candida albicans predicts ARF cycling is essential for drug resistance and virulence

Peer reviewedPublisher PD

Review: Biofilm as a major factor in contamination of milk and dairy products with thermoduric bacteria

The primary source of thermoduric bacteria for contamination of milk and dairy products is raw milk. Contamination sources of raw milk are the surface of udder, milking-, cooling- and storage equipments. Inadequate cleaning and storage of milking equipment may cause formation of biofilm on the surfaces which are in contact with milk. Thermoduric bacteria are divided on the basis of their physiological characteristics from thermophilic, mesophilic and psychrophilic bacteria. Thermoduric bacteria in biofilm have favourable conditions for reproduction. Bacteria in biofilm are much more resistant to temperatures and chemicals used on cleaning of equipment. Characteristics of bacteria cells, the cell-surface properties and the properties of fluid suspending bacteria influenced binding of bacteria in biofilm formed on the surface of the equipment. Outgrowth of thermoduric bacteria and contamination of processed milk take place from biofilm formed on the surfaces of regeneration and cooling sections of pasteurizes and from biofilms formed on the surfaces of separators and buffer tanks, which were in contact with milk. Thermoduric bacteria in raw milk undergo the necessary heat treatment and after it, reproducing in biofilms which formed on the surfaces of equipment, they can turn now to the product. Thermoduric bacteria have often negative impact quality of dairy products

Chemogenomic profiling predicts antifungal synergies

Chemotherapies, HIV infections, and treatments to block organ transplant rejection are creating a population of immunocompromised individuals at serious risk of systemic fungal infections. Since single-agent therapies are susceptible to failure due to either inherent or acquired resistance, alternative therapeutic approaches such as multi-agent therapies are needed. We have developed a bioinformatics-driven approach that efficiently predicts compound synergy for such combinatorial therapies. The approach uses chemogenomic profiles in order to identify compound profiles that have a statistically significant degree of similarity to a fluconazole profile. The compounds identified were then experimentally verified to be synergistic with fluconazole and with each other, in both Saccharomyces cerevisiae and the fungal pathogen Candida albicans. Our method is therefore capable of accurately predicting compound synergy to aid the development of combinatorial antifungal therapies

Widespread occurrence of chromosomal aneuploidy following the routine production of Candida albicans mutants

It has come to our attention that approximately 35% of >100 published microarray datasets, where transcript levels were compared between two different strains, exhibit some form of chromosome-specific bias. While some of these arose from the use of strains whose aneuploidies were not known at the time, in a worrisome number of cases the recombinant strains have acquired additional aneuploidies that were not initially present in the parental strain. The aneuploidies often affected a different chromosome than the one harboring the insertion site. The affected strains originated from either CAI-4, RM1000, BWP17 or SN95 and were produced through a variety of strategies. These observations suggest that aneuploidies frequently occur during the production of recombinant strains and have an effect on global transcript profiles outside of the afflicted chromosome(s), thus raising the possibility of unintended phenotypic consequences. Thus, we propose that all Candida albicans mutants and strains should be tested for aneuploidy before being used in further studies. To this end, we describe a new rapid testing method, based on a multiplex quantitative PCR assay, that produces eight bands of distinct sizes from either the left or right arms of each C. albicans chromosome

Functional genomics in Candida albicans: tackling drug resistance and morphology

The human fungal pathogen Candida albicans is a diploid organism that lacks a complete sexual cycle, thus making functional genetics challenging. Consequently, linking a function to a gene often relies on predictions from other model organisms. In this thesis, I have explored different genetic strategies to address two important aspects of the biology of C. albicans, drug resistance and morphology, which are associated with virulence. Using a reverse genetics approach based on the model Saccharomyces cerevisiae, I first identify and validate a new drug target in C. albicans. Next, I use forward genetics screening directly in the pathogen to identify genes regulating morphology by showing that the Arp2/3 complex is required for the yeast-to-hyphae switch as well as virulence. Lastly, I follow up on the Arp2/3 complex and demonstrate how this fungus can be used to study some unique cell biological aspects regarding actin dynamics and endocytosis. Collectively, this thesis illustrates how various genomic techniques can be applied to understand different aspects of this human fungal pathogen.La levure pathogène Candida albicans est un organisme diploïde n'ayant pas de cycle sexuel complet, ce qui rend difficile la génétique fonctionnelle. Par conséquence, la liaison d'un gène à une fonction repose souvent sur des prévisions à partir d'autres organismes modèles. Dans cette thèse, j'ai exploré différentes stratégies génétiques afin d'étudier deux aspects importants de la biologie de C. albicans, la résistance aux médicaments et la morphologie, qui est associée à la virulence. Avec l'aide d'une approche de génétique inverse basée sur l'organisme modèle Saccharomyces cerevisiae, j'ai d'abord identifié et validé une nouvelle cible thérapeutique chez C. albicans. Ensuite, j'ai utilisé la génétique directe de C. albicans pour identifier des gènes qui régulent sa morphologie. Ceci m'a permis de montrer que le complexe Arp2/3 est requis pour la formation des hyphes ainsi que la virulence. Enfin, je me suis concentré sur le complexe Arp2/3 et j'ai démontré que cette levure peut être utilisée pour étudier certains aspects unique de sa biologiques cellulaire, en particulier, la dynamique de l'actine et l'endocytose. Collectivement, cette thèse montre comment diverses techniques de génétique et de génomique peuvent être appliquées afin de comprendre différents aspects de ce pathogène fongique humain

Correlation of Health Indicators on Lithium‐Ion Batteries

Herein, a detailed correlation index of health indicators for lithium-ion batteries is presented. Identifying potential correlations of health indicators is of high importance with regard to the cell selection process and to minimize the occurring cell-to-cell spread within the lifetime. Health indicators that are taken into account are among others impedance measurements of different pulse lengths, capacity values at different discharge procedures and checkups, weight, and initial voltage. Herein, the work is based on four different aging datasets covering variations in cell chemistry (NMC, LFP, NCA), cell type (round, prismatic), as well as the size and designated application (consumer, automotive). A publicly available dataset is included to allow for an easy reproduction of the results

The zinc cluster transcription factor Ahr1p directs Mcm1p regulation of Candida albicans adhesion

Biofilm development by Candida albicans requires cell adhesion for the initial establishment of the biofilm and the continued stability after hyphal development occurs; however, the regulation of the process has not been fully established. Using chromatin immunoprecipitation coupled to microarray analysis (ChIP-chip) we have characterized a regulon containing the Mcm1p factor that is required for the initial surface adhesion during biofilm formation. In the yeast Saccharomyces cerevisiae several Mcm1p regulons have been characterized in which regulatory specificity is achieved through cofactors binding a sequence adjacent to the Mcm1p binding site. This new Mcm1p regulon in C. albicans also requires a cofactor, which we identify as the transcription factor Ahr1p. However, in contrast to the other yeast regulons, Ahr1p alone binds the target promoters, which include several key adhesion genes, and recruits Mcm1p to these sites. Through transcription profiling and qPCR analysis, we demonstrate that this Ahr1p\u2013Mcm1p complex directly activates these adhesion genes. When the regulatory circuit was disrupted by deleting AHR1, the strain displayed reduced adherence to a polystyrene surface. We also demonstrate a role for the regulon in hyphal growth and in virulence. Our work thus establishes a new mechanism of Mcm1p-directed regulation distinct from those observed for other Mcm1p co-regulators.Peer reviewed: YesNRC publication: Ye