Pigment production by Cryptococcus neoformans from para- and ortho-Diphenols: effect of the nitrogen source

Abstract

Cryptococcus neoformans produced pigments when p-diphenols were substrates in a glucose-amino acid-salts medium. The best substrates were 2.5-dihydroxybenzoic acid and 2,5-dihydroxybenzenesulfonic acid. In contrast to the cellular pigment production from o-diphenols (hydroxyl groups in the 2,3- or 3,4-position of phenyl ring), the p-diphenols (1,4- or 2,5-positions for the hydroxyl groups) produced large amounts of soluble pigments that diffused into the medium. When an optimal source of nitrogen (glutamine, glycine, and asparagine) was used, 89% of the C. neoformans strains produced pigments from p-diphenols. In contrast, 0 to 67% of the strains produced pigments when a suboptimal nitrogen source (proline, ammonium sulfate, ornithine, and methionine) was used. When glutamine-glycine-asparagine was the nitrogen source, 100% of the C. neoformans strains produced pigments from o0diphenols, whereas 77 to 100% of the strains produced pigment when proline-ammonium sulfate-ornithine-methionine was the nitrogen source. Cryptococcus species other than C. neoformans and all tested Candida species failed to produce pigments from any of the substrates except when hydroquinone was used. A combination of glutamine-glycine-asparagine and 3,4-dihydroxyphenylalanine allowed differentiation of colonies of C. neoformans from C. albicans in 3 to 6 days. These data showed that pigment production from o- and p-diphenols served as an excellent biochemical test for the identification of C. neoformans.