This study investigated cyanide production and degradation by isolate W2 of the snow mould basidiomycete fungus grown in shake cultures. The fungus produced cyanide only at the start of the stationary phase when cultured on glucose-containing synthetic medium where growth ceased due to glucose depletion. Cyanogenesis was stimulated by adding glycine to the medium, but methionine provided minimal additional stimulation. When acetate was the carbon source, cyanide was produced during active growth and stationary phase. Using radioactive tracers, [2-14C]glycine was converted to [14C]cyanide during stationary phase, while [1-14C]glycine was converted to CO2 during growth phases. The fungus degraded cyanide primarily by converting it to CO2 as the major detoxification product, with minimal formation of amino acid derivatives or other previously proposed products. Few cyanohydrins of glyoxylic or pyruvic acid were detected. These findings demonstrate that cyanide production in this snow mould fungus follows a secondary metabolite pattern, occurring during the idiophase after primary growth, and that the fungus efficiently detoxifies cyanide through oxidative conversion to CO2 rather than through amino acid biosynthesis pathways.

Key findings

• Cyanide production by the snow mould fungus occurs during stationary phase after glucose depletion, characteristic of secondary metabolite synthesis, and is markedly stimulated by glycine addition to the growth medium
• [2-14C]glycine serves as the direct precursor for cyanide formation during stationary phase, while [1-14C]glycine is catabolized to CO2 during active growth
• The major cyanide detoxification pathway in this fungus is oxidative conversion to CO2, with minimal formation of amino acid derivatives or other previously proposed cyanide assimilation products
• Cyanide production occurs during active growth when acetate is the carbon source, suggesting glucose catabolite repression may regulate this secondary metabolite synthesis
• Unlike cyanogenic bacteria, cyanide production by this fungus is insensitive to medium phosphate and Fe2+ concentrations and is not stimulated by methionine addition