Deoxyribonucleic Acid Relatedness Among Species of Saccharomyces Sensu Lato

Abstract

The generic name Saccharomyces was introduced by Meyen (1838) and defined by Reess (1870). Over the years, the genus included a variable number of phylogenetically heterogeneous species. From about 21 species (Guilliermond, 1912), the genus grew to 30 species and 3 varieties (Lodder and Kreger-van Rij, 1952), and then to 41 species and 6 varieties (van der Walt, 1970). Recently, an extensive reevaluation of the genus left only 7 accepted species (Yarrow, 1984a). During this time, the genus was alternately reorganized and divided. Van der Walt (1965) placed many species in the newly established taxon Kluyveromyces on the basis of spore shape and ascus fragility. Later, Saccharomyces was subdivided into four variously related groups (van der Walt, 1970; Yarrow and Nakase, 1975). Group I represented Saccharomyces sensu stricto and included those species closely related to S. cerevisiae Meyen ex Hansen. These species were subsequently reduced to synonymy with S. cerevisiae on the basis of physiological, morphological and mol % guanine plus cytosine (G+ C) similarities, as well as an absence of reproductive isolation (Naumov, 1969; Yarrow and Nakase, 1975; Yarrow, 1984a). This was partially confirmed by several nuclear deoxyribonucleic acid (nDNA) reassociation studies (Rosini et al., 1982; Vaughan Martini and Kurtzman, 1985; Vaughan Martini and Martini, 1987), although the number of species within the group was found to be actually three: S. cerevisiae, S. bayanus Sacc. and S. pastorianus Hansen. Group II included species closely related to S. bailii Linden, and which are presently assigned to the newly reestablished genus, Zygosaccharomyces (van der Walt and Johannsen, 1975; Yarrow, 1984a). Group III, on the other hand, comprised strains related to S. rosei (Guill.) Lodder et Kreger-van Rij and these species are presently part of the genus Torulaspora (Yarrow, 1984b). Group IV comprised a number of phylogenetically heterogeneous species, and of the 10 listed in the 1970 edition of The Yeasts: A Taxo-