Effects of caffeic acid and hispidin on the light emission intensity of mycelia and luminescent systems of the Neonothopanus nambi and Armillaria borealis basidiomycetes

Abstract

The past decade has seen major advances in research of fungal bioluminescence; however, some biochemical aspects of this phenomenon remain insufficiently understood and need to be studied more thoroughly. In fungi, caffeic acid is a precursor to hispidin, and hispidin, in turn, is a precursor to fungal luciferin. The aim of this work was to study the effects of caffeic acid and hispidin on the intensity of fungal bioluminescence in vivo and in vitro. In vivo experiments demonstrated that caffeic acid stimulates luminescence of mycelia in the basidiomycetes Neonothopanus nambi and Armillaria borealis, increasing the intensity of light emission by at least one order of magnitude. The rapid increase in the level of luminescence in mycelia upon the addition of caffeic acid suggests that this compound interacts with extracellular fungal enzymes, which are located on the surface or within the surface structures of the basidiomycete cell wall. It is hypothesized that the activation of fungal luminescence in vivo may be caused by the oxidation of caffeic acid by ligninolytic oxidases of basidiomycetes (peroxidases, in particular), resulting in the generation of visible light quanta. In contrast, the in vivo study showed that the addition of hispidin, a known precursor of luciferin in the light emission reaction in higher fungi, did not change the level of light emission in N. nambi and A. borealis mycelia. In vitro experiments demonstrated that caffeic acid did not affect the intensity of light emission in the enzymatic luminescent systems extracted from N. nambi and A. borealis mycelia in the presence of NADPH, and considerably inhibited NADPH-hispidin-activated light emission in these systems. Results obtained in the current study give new insights into the mechanisms of light emission in higher fungi and suggest that generation of visible light quanta in basidiomycetes can occur via different biochemical pathways, involving various enzymes and substrates.