Character analyses of selected red yeasts

Editor: G. S. De Hoog
Details: 74 pp., paperback, 1982

The taxonomy of yeast anamorphs has made considerable progress during the last decennia. Important steps forward have been the recognition of ascomycetous and basidiomycetous relationships by means of fundamental asexual characters, particularly the %G+C of DNA, the coenzyme Q system, the mitotic process, the ultrastructure of cell walls and septa, and the carbohydrate composition of cells. On the basis of these characters the anamorphs are now being reclassified in newly defined anamorph genera of either ascomycetous or basidiomycetous affinity. A major problem is that the above characters are normally applicable only at or above the generic level. For classification and identification of yeast anamorphs the physiological diagnostic system has therefore remained in use. Electrophoresis of enzymes (Yamazaki & Komagata, 1981) may be developed as an important supportive taxonomic tool. Another problem is the demarcation of yeasts and hyphomycetes. In the yeast-like hyphomycetes, the widely divergent approaches of students of either groups pose a hindrance towards the taxonomic clarification of these fungi. Thus far few attempts have been made to apply recent methods of hyphomycete taxonomy, mainly conidiogenesis, to the yeasts, and vice versa (von Arx & Weijman, 1979; Sesma & Ramírez, 1978). Nevertheless, the combination of these approaches is necessary to compare yeast-like hyphomycetes with representatives of both groups. For the present project a set of basidiomycetous yeasts was studied with the aim to determine their variability and character structure. The teleomorphs and life cycles had become known previously, particularly through the excellent publications by Banno (1967), Fell and co-workers (Fell et al., 1969, 1973; Fell & Tallman, 1980, 1981) and Kwon-Chung (1975, 1976, 1977; Kwon-Chung et al., 1982). The present paper focusses on characters other than those of the sexual state. Some of the characters described here are considered to be trivial by most yeast taxonomists, particularly the morphology of vegetative cells. The anamorphs are studied using the methods and terminology current in hyphomycete taxonomy. Inspired by the found variability in chlamydospore-like structures, a TEM study of thick-walled cells was also carried out. The process of mitosis in Rhodosporidium toruloides Banno was re-analyzed in detail, augmenting earlier profound studies by McCully & Robinow (1972b) in particular. Cell wall carbohydrates have already proved their significance in yeast taxonomy (e.g. Weijman, 1977a,1979). In the present project the variability of this set of characters was investigated. In addition, the overall composition of carotenoids, sterols and fatty acids was determined, in view of a search for components of possible chemotaxonomic significance. Chemical "fingerprinting" by means of pyrolysis mass spectrometry (Py-MS) has been applied to the taxonomy of yeast-like fungi (Weijman, 1977b; de Hoog, 1977). It should be established whether Py-MS presents a new set of characters or whether it reveals characters already determined by other chemotaxonomical methods. Recently Windig et al. (1981a,b) developed a data analysis technique based on factor analysis of a set of spectra and subsequent rotation of the calculated factors, enabling the differences to be expressed in terms of chemical components. In the present project the method was applied to yeasts. All chapters in this issue are based on a single set of red yeast strains, sometimes supplemented with other strains for comparison. The identity of all material was verified with physiological methods by M. Th. Smith, CBS Yeast Division, Delft. The core set was chosen in such a way, that infra-specific variation could be studied in closely related strains (mating partners), as well as the inter-specific variation in more remote strains. The authors are indebted to Drs P. F.M. Elbers, J. W. Fell, C. S. Gutteridge, I. B. Heath, P. G. Kistemaker, A. Kocková-Kratochvílová, L. Rodrigues de Miranda, M. Th. Smith and J. A. Stalpers for critical manuscript reading, and to A. H. G. Gerrits van de Ende, W. van Laar, G. Lindijer and A. Tom for technical assistence. Dr. C. A. N. van Oorschot is acknowledged for correcting the English texts. - G. S. de Hoog.