An ergothioneine mutant in Neurospora crassa indicates that ergothioneine is required for conidial longevity and protection against peroxide during conidial germination

Ergothioneine (EGT) is a histidine derivative with a trimethylated amine and a thiol/thione in the imidazole ring. Although EGT is only synthesized by fungi and some bacteria, it is acquired by animals and plants, via ingestion and absorption, respectively. The function of EGT in eukaryotes has not been determined. To determine the functions of EGT in vivo, I compared an EGT-non-producing strain of Neurospora crassa (DeltaNcEgtA) that was insertionally mutagenized in gene NCU04343.5, with the wild type (OR74A). Compared to the wild type, DeltaNcEgtA is not pleiotropically affected in rate of hyphal elongation in Vogel's medium either with or without ammonium nitrate and in the rate of germination of macroconidia on Vogel's medium. In contrast, germination of DeltaNcEgtA conidia was significantly more sensitive to tert-butyl hydroperoxide than the wild type; germination of 50% (GI 50) of the DeltaNcEgtA conidia was prevented at 2.7 mM tert-butyl hydroperoxide whereas the GI50 for the wild type was 4.7 mM tert-butyl hydroperoxide, or at a 1.7X greater concentration. The superoxide-producer menadione had indistinguishable effects on conidial germination in both strains. Cupric sulfate also had indistinguishable effects on conidial germination and on hyphal growth in both strains. Although five to 21-day-old conidia of both strains germinated 100%, DeltaNcEgtA conidia had significantly (P < 0.001) diminished longevity. Linear regression analysis indicates that germination of the wild type declines to 50% in 35.1 days, in comparison to 24.6 days for the DeltaNcEgtA , which is equivalent to a 30% reduction in conidial life span in the NcEgtA deletion strain. Consequently, the data indicate that endogenous EGT helps to protect conidia during the quiescent period between conidiogenesis and germination. The data further suggest that EGT helps protect conidia during the germination process from the toxicity of peroxide radicals but not from superoxide or Cu2+. Finally, the data are consistent with the hypothesis that endogenous EGT has more impact on conidial survival and germination than on hyphal growth.