Phaffia rhodozyma is a basidiomycetous pink yeast that until recently was found exclusively in slime fluxes of certain broad-leafed trees in the northern hemisphere. The slime fluxes are rich in sugars and other carbohydrates and P. rhodozyma takes advantage of its fermentative abilities to use these substrates.

Slender, non-septate basidium of Xanthophylomyces dendrorhous, the sexual state of Phaffia rhodozyma with two basidiospores. The basidium is formed directly from a yeast cell after conjugation with its bud and hyphae are not formed. © D. Libkind 2008

 One of the most remarkable features of P. rhodozyma is the pink to orange color of its colonies due the production of carotenoid pigments. The main carotenoid pigment produced by P. rhodozyma is astaxanthin, a compound not formed by any other yeast species. Astaxanthin is economically important because it is an aquaculture feed component needed for pigmentation of fish and crustaceans and is the most expensive feed ingredient in the aquaculture industry.

Phaffia astaxanthin is commercially available as a natural source of the carotenoid astaxanthin.

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Very recent work carried out by Diego Libkind in Patagonia (Argentina) has lead to the isolation, for the first time, of P. rhodozyma in the southern hemisphere.

Diego Libkind – Colleague and friend from Universidad Nacional del Comahue, Centro Regional Universitario Bariloche, Argentina.

 The same work has lead to the detection of a new habitat for P. rhodozyma: the sugar-rich fruiting bodies of Cyttaria hariotii, a fungal parasite of trees of the genus Nothofagus.

Cyttaria stromata growing on a Nothofagus trunk. Image credits: http://en.wikipedia.org/wiki/Cyttaria

 We gathered preliminary evidence that different lineages of P. rhodozyma colonize different host trees. Coherent groups based on ITS (rDNA Internal Transcribed Spacer) sequence data were found for the strains isolated from Betulaceae (Betula and Alnus), Cornus, Fagus and Nothofagus / Cyttaria.

Phylogenetic relationships between different isolates of Xantophyllomyces dendrorhous (asexual state: Phaffia rhodozyma) and their plant hosts.

 These findings suggest that genetically different populations of P. rhodozyma, each associated with a different plant host, colonize the same geographical region but do not interbreed. Another interesting observation is the congruence between the ITS phylogenetic trees of Phaffia and its plant hosts.

 Current studies aim at (i) testing the hypothesis that P. rhodozyma encompasses different lineages, each associated with a different plant or fungal host; (ii) validating the claim that the molecular phylogeny of the different lineages of P. rhodozyma reproduces that of its plant hosts and that basal Phaffia lineages are associated with ancestral tree hosts; (iii) calculating the degrees of intra-lineage and inter-lineage genetic recombination; (iv) determining if Phaffia can be found in other regions where Nothofagus and Cyttaria exist and if, besides C. hariotii, other Cyttaria species harbour P. rhodozyma.