Endogenous ergothioneine is required for wild type levels of conidiogenesis and conidial survival but does not protect against 254 nm UV-induced mutagenesis or kill

• The histidine derivative ergothioneine (EGT) is concentrated in Pezizomycotina conidia.
• EGT provides ca. one-third of the water-soluble antioxidant activity in Neurospora crassa conidia.
• N. crassa Egt− strains produce 59 ± 6(SE)% fewer (P < 0.001) conidia than Egt+ strains.
• Egt− conidia stored at 97% and 52% relative humidity have a ca. 20% shorter lifespan than Egt+ conidia.
• EGT does not protect conidia against 254 nm UV light-induced kill or mutagenesis.

Ergothioneine, a histidine derivative, is concentrated in conidia of ascomycetous fungi. To investigate the function of ergothioneine, we crossed the wild type Neurospora crassa (Egt+) and an ergothioneine non-producer (Egt−, Δegt-1, a knockout in NCU04343.5) and used the Egt+ and Egt− progeny strains for phenotypic analyses. Compared to the Egt+ strains, Egt− strains had a 59% reduction in the number of conidia produced on Vogel’s agar. After storage of Egt+ and Egt− conidia at 97% and 52% relative humidity (RH) for a time course to either 17 or 98 days, respectively, Egt− strains had a 23% and a 18% reduction in life expectancy at 97% and 52% RH, respectively, compared to the Egt+ strains. Based on a Cu(II) reduction assay with the chelator bathocuproinedisulfonic acid disodium salt, ergothioneine accounts for 38% and 33% of water-soluble antioxidant capacity in N. crassa conidia from seven and 20 day-old cultures, respectively. In contrast, ergothioneine did not account for significant (α = 0.05) anti-oxidant capacity in mycelia, which have lower concentrations of ergothioneine than conidia. The data are consistent with the hypothesis that ergothioneine has an antioxidant function in vivo. In contrast, experiments on the spontaneous mutation rate in Egt+ and Egt− strains and on the effects of 254 nm UV light on mutation rate and conidial viability do not support the hypothesis that ergothioneine protects DNA in vivo.