Brown pigments produced by Yarrowia lipolytica result from extracellular accumulation of homogentisic acid

Yarrowia lipolytica produces brown extracellular pigments that correlate wi th tyrosine catabolism. During tyrosine depletion, the yeast accumulated ho mogentisic acid, p-hydroxyphenylethanol, and p-hydroxyphenylacetic acid in the medium. Homogentisic acid accumulated under all aeration conditions tes ted, but its concentration decreased as aeration decreased. With moderate a eration, equimolar concentrations of alcohol and p-hydroxyphenylacetic acid (1:1) were detected, but with lower aeration the alcohol concentration was twice that of the acid (2:1). p-Hydroxyphenylethanol and p-hydroxyphenylac etic acid may result from the spontaneous disproportionation of the corresp onding aldehyde, p-hydroxyphenylacetaldehyde. The catabolic pathway of tyro sine in Y. lipolytica involves the formation of p-hydroxyphenylacetaldehyde , which is oxidized to p-hydroxyphenylacetic acid and then further oxidized to homogentisic acid. Brown pigments are produced when homogentisic acid a ccumulates in the medium. This acid can spontaneously oxidize and polymeriz e, leading to the formation of pyomelanins. Ma(2+) accelerated and intensif ied the oxidative polymerization of homogentisic acid, and lactic acid enha nced the stimulating role of Mn2+. Alkaline conditions also accelerated pig ment formation. The proposed tyrosine catabolism pathway appears to be uniq ue for yeast, and this is the first report of a yeast producing pigments in volving homogentisic acid.