Selective destruction of microscopic fungi through photo-oxidation of ergosterol

Ergosterol is an important component of fungal membranes. This sterol can be easily transformed to peroxide of ergosterol by photo-oxidation with singlet oxygen. Cultures of Papalauspora immersa were grown on Czapeck agar medium, and subjected to the following conditions: 1) irradiation with daylight and quartz light (excluding UV light), 2) addition by diffusion of yellowish eosine (0.1 mg/mL), and 3) the control (no yellowish eosine, under darkness conditions). Fungal growth was completely inhibited after the treatment with quartz light (3 h) and yellow eosine, and no growth was observed in subsequent subcultures. These results suggested that plasma membrane components changed significantly by the transformation of ergosterol to peroxide of ergosterol leading to fungal death. To confirm this, a second experiment on a larger scale was carried out in which the fungus was grown on liquid medium in test tubes, treated, irradiated, and tested for peroxide of ergosterol by (1)HNMR. This peroxide was only found in treated samples. These findings represent a new strategy for developing antifungal agents, based on ergosterol photo-oxidation which might probably be related to the disruption of the plasma membrane, instead of only preventing the ergosterol biosynthesis. The potential application of this strategy for the selective control or prevention of pathogenic fungi is considerable.