Alternative Oxidase Promotes Biofilm Formation of Candida albicans

Alternative Oxidase - Aid or obstacle to combat the rise of fungal pathogens?

Fungal pathogens present a growing threat to both humans and global health security alike. Increasing evidence of antifungal resistance in fungal populations that infect both humans and plant species has increased reliance on combination therapies and shown the need for new antifungal therapeutic targets to be investigated. Here, we review the roles of mitochondria and fungal respiration in pathogenesis and discuss the role of the Alternative Oxidase enzyme (Aox) in both human fungal pathogens and phytopathogens. Increasing evidence exists for Aox within mechanisms that underpin fungal virulence. Aox also plays important roles in adaptability that may prove useful within dual targeted fungal-specific therapeutic approaches. As improved fungal specific mitochondrial and Aox inhibitors are under development we may see this as an emerging target for future approaches to tackling the growing challenge of fungal infection.

Caspofungin at Sub-inhibitory Concentration Promotes the Formation of Candida Albicans Persister Cells

AIMS

Low caspofungin exposure is frequently encountered in patients with invasive candidiasis caused by Candida albicans (C. albicans). This study aimed to investigate the effects of caspofungin on C. albicans at sub-inhibitory concentrations.

METHODS AND RESULTS

First, a comparative transcriptomics analysis was performed on C. albicans receiving caspofungin at sub-minimum inhibitory concentrations (sub-MIC). The results showed that caspofungin significantly changed the mRNA expression profile in DAY185, with DE-mRNAs enriched in the functions of cell wall biosynthesis, metabolism, etc. Subsequently, cellular fitness, cell aggregation, energy metabolism activity, and the proportion of persister cells of C. albicans were quantitatively and/or qualitatively assessed after sub-MIC caspofungin exposure. No significant changes in cell fitness and aggregation formation were observed during treatment of C. albicans with sub-MIC caspofungin. In C. albicans aggregation treated with sub-MIC caspofungin, we observed a decrease in respiratory metabolism and an increase in persister cells; this effect was more pronounced in als1ΔΔ than in DAY185.

CONCLUSIONS

Pre-exposure to sub-MIC caspofungin suppresses C. albicans respiratory metabolism and promotes persister cell development.

SIGNIFICANCE AND IMPACT OF STUDY

Caspofungin should be used with caution in patients with C. albicans infections, as anti-infection therapy may fail due to persister cells.

Kinetic characterisation and inhibitor sensitivity of Candida albicans and Candida auris recombinant AOX expressed in a self-assembled proteoliposome system

Candidemia caused by Candida spp. is a serious threat in hospital settings being a major cause of acquired infection and death and a possible contributor to Covid-19 mortality. Candidemia incidence has been rising worldwide following increases in fungicide-resistant pathogens highlighting the need for more effective antifungal agents with novel modes of action. The membrane-bound enzyme alternative oxidase (AOX) promotes fungicide resistance and is absent in humans making it a desirable therapeutic target. However, the lipophilic nature of the AOX substrate (ubiquinol-10) has hindered its kinetic characterisation in physiologically-relevant conditions. Here, we present the purification and expression of recombinant AOXs from C. albicans and C. auris in a self-assembled proteoliposome (PL) system. Kinetic parameters (Km and Vmax) with respect to ubiquinol-10 have been determined. The PL system has also been employed in dose-response assays with novel AOX inhibitors. Such information is critical for the future development of novel treatments for Candidemia.