Parietal composition of Lichtheimia corymbifera: differences between spore and germ tube stages and host-pathogen interactions.

The molecular composition and structural organisation of the cell wall of filamentous fungi underlie the ability of the host to identify them as pathogens. Although the organisation of the fungal cell wall, composed of 90% polysaccharides, is similar from one fungus to another, small variations condition their ability to trigger pattern recognition receptors. Because the incidence of mucormycosis, an emerging life-threatening infection caused by the species of the order Mucorales is increasing worldwide, the precise composition of the cell wall of two strains of Lichtheimia corymbifera was investigated in the early growth stages of germination (spores and germ-tubes) using trimethylsilylation and confocal microscopy. This study also characterises the response of THP-1 cells to Mucorales. The study identified the presence of uncommon monosaccharides (fucose, galactose and glucuronic acid) whose respective proportions vary according to the germination stage, revealing early parietal reorganisation. Immunofluorescence studies confirmed the exposure of β-glucan on the surface of swollen spores and germ-tubes. Both spores and germ-tubes of L. corymbifera promoted an early and strong pro-inflammatory response, through TLR-2. Our results show the singularity of the cell wall of the order Mucorales, opening perspectives for the development of specific diagnostic biomarkers.