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

Kok Lian Ho,Alistair J. P. Brown,Yoke Kqueen Cheah,Shu Yih Chew,Doblin Sandai,Leslie Thian Lung Than,Tzu Shan Ng

doi:10.1038/s41598-019-39117-1

Abstract

The human fungal pathogen Candida glabrata appears to utilise unique stealth, evasion and persistence strategies in subverting the onslaught of host immune response during systemic infection. However, macrophages actively deprive the intracellular fungal pathogen of glucose, and therefore alternative carbon sources probably support the growth and survival of engulfed C. glabrata. The present study aimed to investigate the role of the glyoxylate cycle gene ICL1 in alternative carbon utilisation and its importance for the virulence of C. glabrata. The data showed that disruption of ICL1 rendered C. glabrata unable to utilise acetate, ethanol or oleic acid. In addition, C. glabrata icl1∆ cells displayed significantly reduced biofilm growth in the presence of several alternative carbon sources. It was also found that ICL1 is crucial for the survival of C. glabrata in response to macrophage engulfment. Disruption of ICL1 also conferred a severe attenuation in the virulence of C. glabrata in the mouse model of invasive candidiasis. In conclusion, a functional glyoxylate cycle is essential for C. glabrata to utilise certain alternative carbon sources in vitro and to display full virulence in vivo. This reinforces the view that antifungal drugs that target fungal Icl1 have potential for future therapeutic intervention.

Highlights

Invasive candidiasis is a potentially lethal fungal infection caused by fungi from the Candida genus that is associated with high morbidity and mortality
The ability of C. glabrata American Type Culture Collection (ATCC) 2001, WT and icl1∆ cells to grow on glucose or alternative carbon sources was tested using simple growth assays
We found that ICL1 deletion rendered C. glabrata unable to grow on acetate and ethanol as sole carbon source (Figs 1 and 2)

Summary

Introduction

Invasive candidiasis is a potentially lethal fungal infection caused by fungi from the Candida genus that is associated with high morbidity and mortality. In addition to autophagy and enhanced glucose sensing, alternative carbon utilisation is believed to be important for the survival and pathogenicity of Candida species. Transcriptional analyses of C. albicans and C. glabrata revealed extensive metabolic reprogramming that reflects adaptation to nutrient deprivation following macrophages engulfment[14,15] This reprogramming includes the upregulation of genes from three interconnected alternative carbon utilisation pathways: gluconeogenesis (FBP1 and PCK1), the glyoxylate cycle (ICL1 and MLS1) and fatty acid β-oxidation (FOX2 and POX1). Upregulation of these pathways indicates that the macrophage actively deprives C. albicans and C. glabrata of their preferable carbon source, forcing these fungal pathogens to tune their metabolism to alternative carbon sources. Isocitrate lyase is required for Salmonella enterica serovar Typhimurium during chronic infection and is essential for the virulence of Rhodococcus equi and Pseudomonas aeruginosa[21,22,23]

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Results

Conclusion