Disruption of Protein Mannosylation Affects Candida guilliermondii Cell Wall, Immune Sensing, and Virulence

Abstract

The fungal cell wall contains glycoproteins that interact with the host immune system. In the prominent pathogenic yeast Candida albicans, Pmr1 acts as a Golgi-resident ion pump that provides cofactors to mannosyltransferases, regulating the synthesis of mannans attached to glycoproteins. To gain insight into a putative conservation of such a crucial process within opportunistic yeasts, we were particularly interested in studying the role of the PMR1 homolog in a low-virulent species that rarely causes candidiasis, Candida guilliermondii. We disrupted C. guilliermondii PMR1 and found that loss of Pmr1 affected cell growth and morphology, biofilm formation, susceptibility to cell wall perturbing agents, mannan levels, and the wall composition and organization. Despite the significant increment in the amount of β1,3-glucan exposed at the wall surface, this positively influenced only the ability of the mutant to stimulate IL-10 production by human monocytes, suggesting that recognition of both mannan and β1,3-glucan, is required to stimulate strong levels of pro-inflammatory cytokines. Accordingly, our results indicate C. guilliermondii sensing by monocytes was critically dependent on the recognition of N-linked mannans and β1,3-glucan, as reported in other Candida species. In addition, chemical remotion of cell wall O-linked mannans was found to positively influence the recognition of C. guilliermondii by human monocytes, suggesting that O-linked mannans mask other cell wall components from immune cells. This observation contrasts with that reported in C. albicans. Finally, mice infected with C. guilliermondii pmr1Δ null mutant cells had significantly lower fungal burdens compared to animals challenged with the parental strain. Accordingly, the null mutant showed inability to kill larvae in the Galleria mellonella infection model. This study thus demonstrates that mannans are relevant for the C. guilliermondii-host interaction, with an atypical role for O-linked mannans.

Early Virulence Predictors during the Candida Species–Galleria mellonella Interaction

“…It is possible to hypothesize that the strong activation of these humoral effectors involves resources reassignment to this humoral response, with detrimental effects on the insect fitness. In addition, it has been suggested that phenoloxidase activity, and therefore melanization, could be activated by recognition of cell wall β-glucan [ 33 ], and the exposure of this polysaccharide can vary depending on the fungal species analyzed [ 3 , 4 , 21 , 22 ].…”

“…G. mellonella larvae have thermotolerance and can grow at 37 °C, which represents an advantage to study Candida spp. thermoadaptation and temperature related-factors, including dimorphism [ 15 , 18 , 19 , 20 , 21 , 22 ], and the G. mellonella hemocytes, which are immunological cells found in the hemolymph, can perform fungal phagocytosis like mammalian macrophages, and even Candida cells can use similar strategies to evade killing in both hemocytes and macrophages [ 15 , 23 , 24 ]. Moreover, these larvae have demonstrated to be a proper host to evaluate the effect of antifungal drugs and new compounds with antifungal properties on the host–fungus interaction [ 25 , 26 , 27 ].…”

“…The most frequent parameters evaluated during the Candida – G. mellonella interaction are the time taken to kill the animal population, the fungal burden recovered from infected animals, and the expression of genes related to humoral immune factors, such as antimicrobial peptides [ 18 , 19 , 20 , 21 , 22 , 32 ]. To generate killing curves, an observation period of two weeks is usually required, in particular when the fungal strains show virulence attenuation [ 18 , 19 , 20 , 21 , 22 ]. Furthermore, reductions in circulating hemocytes, melanin production, and phenoloxidase activity have been observed in infected larvae [ 33 ].…”

Immunity to Candida Infection: An Overview

“…Disruption of Protein mannosylation affects C. guilliermondii Cell Wall, Immune Sensing, and Virulence [18].…”

Immunity to Candida Infection: An Overview

“…Recently, Navarro-Arias et al [18] reported that mannans are relevant for the C. guilliermondii-host interaction. Disruption of Protein mannosylation affects C. guilliermondii Cell Wall, Immune Sensing, and Virulence [18].…”