A metabolomic study of the effect of Candida albicans glutamate dehydrogenase deletion on growth and morphogenesis

Ting-Li Han,Richard D Cannon,Sandra M Gallo,Silas G Villas-Bôas

doi:10.1038/s41522-019-0086-5

Abstract

There are two glutamate dehydrogenases in the pathogenic fungus Candida albicans. One is an NAD+-dependent glutamate dehydrogenase (GDH2) and the other is an NADPH-dependent glutamate dehydrogenase (GDH3). These two enzymes are part of the nitrogen and nicotinate/nicotinamide metabolic pathways, which have been identified in our previous studies as potentially playing an important role in C. albicans morphogenesis. In this study, we created single gene knockout mutants of both dehydrogenases in order to investigate whether or not they affect the morphogenesis of C. albicans. The GDH genes were deleted and the phenotypes of the knockout mutants were studied by growth characterisation, metabolomics, isotope labelling experiments, and by quantifying cofactors under various hyphae-inducing conditions. We found that the gdh2/gdh2 mutant was unable to grow on either arginine or proline as a sole carbon and nitrogen source. While the gdh3/gdh3 mutant could grow on these carbon and nitrogen sources, the strain was locked in the yeast morphology in proline-containing medium. We detected different concentrations of ATP, NAD+, NADH, NAPD+, NADPH, as well as 62 other metabolites, and 19 isotopically labelled metabolites between the mutant and the wild-type strains. These differences were associated with 44 known metabolic pathways. It appears that the disequilibrium of cofactors in the gdh3/gdh3 mutant leads to characteristic proline degradation in the central carbon metabolism. The analysis of the gdh2/gdh2 and the gdh3/gdh3 mutants confirmed our hypothesis that redox potential and nitrogen metabolism are related to filament formation and identified these metabolic pathways as potential drug targets to inhibit morphogenesis.

Highlights

Candida albicans is a polymorphic fungus that grows on various human mucosal surfaces
This study implicates GDH2 and GDH3 gene knockout mutagenesis, metabolomics, and isotope labelling approaches to elucidate how the fungus C. albicans changes its cellular metabolism during the yeast-to-hyphal transition
There were three major comparisons performed in this study in order to determine the role of GDH2 and GDH3 in C. albicans growth and morphogenesis

Summary

Introduction

Candida albicans is a polymorphic fungus that grows on various human mucosal surfaces. The morphological switch from budding yeast to filamentous forms is often associated with its biological adaptation as an opportunistic pathogen of humans. C. albicans yeast cells are capable of surviving during phagocytosis by triggering filamentous growth and eventually bursting out of the macrophage or neutrophil[4,5]. In our previous studies[6,7,8], we have demonstrated that during the yeast-to-hyphal transition the central carbon metabolism of C. albicans is globally downregulated. The pathways involved in the metabolism of alanine, β-alanine, aspartate, cysteine, histidine, glutamate, methionine, nitrogen, and nicotinate/nicotinamide, as well as the biosynthesis of acetyl-CoA are repressed. By using an isotope labelling experiment to trace the catabolism of the quorum sensing molecule phenylethyl alcohol, that represses hyphae formation under hyphae-inducing conditions, we have found strong evidence for the involvement of

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Conclusion