Melanization affects susceptibility of Cryptococcus neoformans to heat and cold

Cryptococcus neoformans can synthesize melanin from a variety of substrates, including L-dopa (L-3,4-dihydroxyphenylalanine). Growth in minimal medium with L-dopa resulted in progressive accumulation of melanin in stationary phase cells. Melanized and non-melanized yeast cells were exposed to heat (42-47 degrees C) and cold (-20 degrees C), and the percentage of survival determined. Melanized cells were less susceptible to heat than non-melanized cells of the same age. Melanized cells from early stationary phase cultures were less susceptible to cold than non-melanized cells of the same age. However, melanized cells from late stationary phase cultures were more susceptible to cold than non-melanized cells of the same age. There was no statistical difference in susceptibility to heat and cold between melanin-deficient cells grown with and without L-dopa. These results suggest a role for melanin in protection against heat and cold.