Deoxyribonucleic acid (DNA) base composition and DNA base sequence relatedness comparisons were used for species delineation in the genus Kluyveromyces. Base composition values separated the members of the genus into three groups. The groups were further subdivided by comparing base sequences by using DNA/DNA renaturation experiments. Two DNA homology groups were identified. The first group included Kluyveromyces marxianus, Kluyveromyces fragilis, Kluyveromyces bulgaricus, Kluyveromyces cicerisporus, Kluyveromyces wikenii, and three anamorphs (Candida kefyr, Candida pseudotropicalis, and Torula cremoris); the members of this group exhibited ≥90% DNA base sequence complementarity. The second group consisted of Kluyveromyces lactis, Kluyveromyces vanudenii, Kluyveromyces drosophilarum, and Kluyveromyces phaseolosporus; various pairs of these yeasts shared 64 to 98% of their DNA sequences. The two groups were only distantly related to each other (≤15% DNA base sequence complementarity). The other Kluyveromyces species appear to be unique, not being closely related to either of the two homology groups or to one another. Relationships deduced from comparisons of DNAs agreed well with those deduced by other workers from immunological comparisons of exo-β-glucanases and from isoenzyme analysis but were only in partial agreement with a taxonomic arrangement made on the basis of mating studies. We propose recognition of the following species: Kluyveromyces aestuarii, Kluyveromyces africanus, Kluyveromyces blattae, Kluyveromyces delphensis, Kluyveromyces dobzhanskii, K. lactis (syn. K. drosophilarum, K. phaseolosporus, and K. vanudenii), Kluyveromyces lodderi, K. marxianus (syn. K. bulgaricus, K. cicerisporus, K. fragilis, and K. wikenii), Kluyveromyces phaffii, Kluyveromyces polysporus, Kluyveromyces thermotolerans, Kluyveromyces waltii, and Kluyveromyces wickerhamii.
Deoxyribonucleic acid relatedness among the type strains of all taxa and known anamorphs assigned to the yeast genus Kluyveromyces was assessed by the optical reassociation technique. Three groups of species related at the 95% level or higher were found: (i) K. lactis including K. drosophilarum, K. phaseolosporus, K. vanudeni, and the anamorph Candida sphaerica; (ii) K. marxianus with K. bulgaricus, K. cicerisporus, K. fragilis, K. wikenii, and the anamorphs Candida kefyr, Candida macedoniensis, and Candida pseudotropicalis; (iii) K. thermotolerans with K. veronae and the anamorph Candida dattila. The remaining species, including the recently described K. blattae and K. waltii, are not related to each other or to the members of the above three groups. The nomen nudum K. cellobiovorus is not conspecific with any of the species of the genus. The species assignment obtained by nuclear deoxyribonucleic acid reassociation does not entirely conform with the previously proposed reorganization of the genus Kluyveromyces (J.-P. van der Walt and E. Johannsen, p. 224–251, in N. J. W. Kreger-van Rij, ed., The Yeasts. A Taxonomic Study, 1984).
We describe Pichia barkeri, a new cactophilic yeast species occurring in necrotic tissue of Opuntia stricta in New South Wales, Australia, and on several islands in the Caribbean Sea. The new species is homothallic and appears to occur in nature in the haploid state. After conjugation between a mother cell and a bud, four hat-shaped spores are produced that are rapidly released from the ascus. The range of guanine-plus-cytosine contents for the nuclear deoxyribonucleic acids of 22 strains is 35.7 to 36.6 mol% (average, 36.1 mol%; standard deviation, 0.2 mol%). The type strain of P. barkeri is strain UCD-FST 83-994.3 (ATCC 64111, CBS 7256) isolated at Discovery Bay, Jamaica.