Biogeography, Host Specificity, and Molecular Phylogeny of the Basidiomycetous Yeast Phaffia rhodozyma and Its Sexual Form, Xanthophyllomyces dendrorhous

Abstract

Phaffia rhodozyma (sexual form, Xanthophyllomyces dendrorhous) is a basidiomycetous yeast that has been found in tree exudates in the Northern Hemisphere at high altitudes and latitudes. This yeast produces astaxanthin, a carotenoid pigment with biotechnological importance because it is used in aquaculture for fish pigmentation. We isolated X. dendrorhous from the Southern Hemisphere (Patagonia, Argentina), where it was associated with fruiting bodies of Cyttaria hariotii, an ascomycetous parasite of Nothofagus trees. We compared internal transcribed spacer (ITS)-based phylogenies of P. rhodozyma and its tree host (Betulaceae, Corneaceae, Fagaceae, and Nothofagaceae) and found them to be generally concordant, suggesting that different yeast lineages colonize different trees and providing an explanation for the phylogenetic distance observed between the type strains of P. rhodozyma and X. dendrorhous. We hypothesize that the association of Xanthophyllomyces with Cyttaria derives from a previous association of the yeast with Nothofagus, and the sister relationship between Nothofagaceae and Betulaceae plus Fagaceae correlates with the phylogeny of X. dendrorhous strains originating from these three plant families. The two most basal strains of X. dendrorhous are those isolated from Cornus, an ancestral genus in the phylogenetic analysis of the host trees. Thus, we question previous conclusions that P. rhodozyma and X. dendrorhous represent different species since the polymorphisms detected in the ITS and intergenic spacer sequences can be attributed to intraspecific variation associated with host specificity. Our study provides a deeper understanding of Phaffia biogeography, ecology, and molecular phylogeny. Such knowledge is essential for the comprehension of many aspects of the biology of this organism and will facilitate the study of astaxanthin production within an evolutionary and ecological framework.Phaffia rhodozyma was originally isolated in the late 1960s, by Phaff and collaborators, who collected 10 strains from various broad-leafed trees in mountainous regions of Japan and Alaska (23). These strains had a red to orange color and could ferment glucose and produce amyloid compounds. Phaff et al. (23) referred to these strains as Rhodozyma montanae, but since a Latin diagnosis was not provided, the name was not valid. Later, this basidiomycetous yeast was described as Phaffia rhodozyma (20), and 67 additional strains were isolated from spring sap flows of Betula verrucosa in Russia (10).The main carotenoid pigment produced by P. rhodozyma is astaxanthin, a compound that has not been found in other yeast species (3). Astaxanthin is economically important as an aquaculture feed component. This compound enhances pigmentation of fish and crustaceans (19) and is the most expensive feed ingredient in the aquaculture industry (12). Studies of the feasibility of P. rhodozyma as a dietary source of this pigment began almost 30 years ago (13). Such studies involved the development of methods for optimizing pigment...

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