Yarrowia lipolytica produces brown extracellular pigments that correlate with tyrosine catabolism. During tyrosine depletion, the yeast accumulated homogentisic acid, p-hydroxyphenylethanol, and p-hydroxyphenylacetic acid in the medium. Homogentisic acid accumulated under all aeration conditions tested, but its concentration decreased as aeration decreased. With moderate aeration, 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-hydroxyphenylacetic acid may result from the spontaneous disproportionation of the corresponding aldehyde, p-hydroxyphenylacetaldehyde. The catabolic pathway of tyrosine in Y. lipolytica involves the formation of p-hydroxyphenylacetaldehyde, which is oxidized to phydroxyphenylacetic acid and then further oxidized to homogentisic acid. Brown pigments are produced when homogentisic acid accumulates in the medium. This acid can spontaneously oxidize and polymerize, leading to the formation of pyomelanins. Mn 2؉ accelerated and intensified the oxidative polymerization of homogentisic acid, and lactic acid enhanced the stimulating role of Mn 2؉ . Alkaline conditions also accelerated pigment formation. The proposed tyrosine catabolism pathway appears to be unique for yeast, and this is the first report of a yeast producing pigments involving homogentisic acid.Brown discoloration is a common defect in cheese. Yarrowia lipolytica is thought to be responsible for this discoloration in traditional Portuguese ewes' cheeses (7), Camembert (11), and Gorgonzola-type cheeses (27). The spoilage activity of this species seems to be related to its ability to produce brown pigments from tyrosine (5), but little is known of the mechanism involved.Brown pigments produced from tyrosine are known as melanins. This is a general term that includes a wide variety of complex polyphenolic heteropolymers. Microorganisms may form melanin via L-tyrosine catabolism (8,13,32,33) or a tyrosinase (EC 1.14.18.1)-mediated pathway (17,21,26,29,31,37). In bacteria, tyrosine is degraded via pathways that involve either homoprotocatechuic (3,4-dihydroxyphenylacetic) acid (34) or homogentisic (2,5-dihydroxyphenylacetic) acid (HGA) (4, 30) as intermediates. Both of these intermediates can be melanin precursors, and their accumulation usually results from an enzymatic disruption of these pathways. Brown pigments are formed from the oxidation and polymerization of these intermediates (8,13,32,33,35,36).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. 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 ...

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.

No abstract

There are literally hundreds of polypeptides described in the literature which exhibit fungicide activity. Tens of them have had attempted protection by patent applications but none, as far as we are aware, have found application under real agricultural conditions. The reasons behind may be multiple where the sensitivity to the Sun UV radiation can come in first place. Here we describe a multifunctional glyco-oligomer with 210 kDa which is mainly composed by a 20 kDa polypeptide termed Blad that has been previously shown to be a stable intermediary product of β-conglutin catabolism. This oligomer accumulates exclusively in the cotyledons of Lupinus species, between days 4 and 12 after the onset of germination. Blad-oligomer reveals a plethora of biochemical properties, like lectin and catalytic activities, which are not unusual per si, but are remarkable when found to coexist in the same protein molecule. With this vast range of chemical characteristics, antifungal activity arises almost as a natural consequence. The biological significance and potential technological applications of Blad-oligomer as a plant fungicide to agriculture, its uniqueness stems from being of polypeptidic in nature, and with efficacies which are either equal or greater than the top fungicides currently in the market are addressed.

Experimental Camembert cheeses were made to investigate the effects on browning of the following factors: inoculation with Yarrowia lipolytica, the use of Penicillium candidum strains with different proteolytic activity, the addition of tyrosine, and the addition of Mn2+, thus leading to 16 different variants of cheese. Two physical colour parameters were used to describe browning, depending on the location in the cheeses: a whiteness index for the outside browning (mould mycelium), and a brownness index for the inside browning (surface of the cheese body). Mn2+ promoted a significant increase of browning at both locations, whereas Yar. lipolytica had the opposite effect. Outside browning was significantly more intense when using the Pen. candidum strain with higher proteolytic activity. A significant interaction was found between Yar. lipolytica and Pen. candidum. The yeast had no effect in combination with a low proteolytic strain of Pen. candidum, but significantly reduced proteolysis and browning in combination with a high proteolytic strain of Pen. candidum. We further confirmed that both strains of Pen. candidum were able to produce brown pigments from tyrosine, and thus both are presumably responsible for the browning activity in this type of cheese.