Production of brown tyrosine pigments by the yeast Yarrowia lipolytica

Abstract

Aims: To study the mechanism of production of brown pigments from tyrosine in the yeast Yarrowia lipolytica. Methods and Results: Pigment formation was followed during growth in tyrosine medium, and the presence of the pigment precursor in the medium was assessed by evaluating pigment formation after removing the cells at different times of incubation. It was observed that the pigment precursor accumulated outside the cells during the exponential phase of growth, but pigment formation only occurred during the stationary phase of growth and resulted from the oxidation of the precursor. Pigment formation was repressed by glucose and L L-glutamine, and promoted by lactic acid, L L-asparagine and glycine. Spectra of 1 H and 13 C-NMR revealed that the brown pigment was derived from tyrosine and was a polymer composed of a core of aromatic residues. Conclusions: The results indicate that pigments result from the extracellular accumulation and auto-oxidation of an intermediate of tyrosine catabolism. Signi®cance and Impact of the Study: This is the ®rst report on the mechanism of pigment production from tyrosine in a yeast species.

Brown Pigments Produced by Yarrowia lipolytica Result from Extracellular Accumulation of Homogentisic Acid

“…Since the chemical structure of melanins is still unknown and pyomelanin formation is presently proved by detecting the formation of HGA from tyrosine (8,18,36), it seems likely that the pigments of Y. lipolytica are pyomelanins. Furthermore, we have previously demonstrated that these pigments are polymers in which the main monomer is derived from tyrosine and has a general chemical structure compatible with the structure of HGA (6). To the best of our knowledge, the involvement of HGA in the production of brown pigments has not been reported for fungi.…”

“…The involvement of Y. lipolytica in the browning defects of cheese seems to result from its ability to produce brown pigments from tyrosine (6,27). The technological conditions under which browning develops are not yet established, and it remains unclear why this phenomenon has a sporadic occurrence even in cheeses where this species is usually present.…”

“…Tyrosine medium was used under controlled pH conditions (pH 4.8) in order to slow the increase in pH that occurs when Y. lipolytica is grown on this type of medium (5,6). This procedure is needed to stabilize aromatic compounds that would otherwise oxidize at high pH.…”

“…Melanin production in Y. lipolytica is reported to result from L-tyrosine degradation (6). It is a two-stage process in which the pigment precursor is first accumulated outside the cells and then autooxidizes and polymerizes.…”

“…It is a two-stage process in which the pigment precursor is first accumulated outside the cells and then autooxidizes and polymerizes. The chemical core of the resulting pigment has a structure typical of an intermediate of tyrosine catabolism, and this structure or compound seems to be the main monomer in the polymer (6). We hypothesize that HGA is the precursor or intermediate involved, since a mutant strain of Y. lipolytica unable to use tyrosine as the sole carbon source is known to accumulate this acid in a tyrosine-containing medium (2).…”