Ming Zhan

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The Phylogeny of Kluyveromyces was studied by partial sequencing the ribosomal RNA gene.;The gene coding for the divergent domain II (D2) of nuclear LSU rRNA was amplified by polymerase chain reaction (PCR) for Kluyveromyces and other yeasts. The PCR products were cloned and sequenced. The sequence data were analyzed by the neighbour-joining, Fitch-Margoliash, maximum likelihood, parsimony and compatibility methods of phylogenetic inference. The final conclusions of the analyses were drawn from the consensus of the various phylogenies confirmed to be reliable by bootstrap tests.;The genus Kluyveromyces is polyphyletic. The species of this genus probably evolved from three distinct ancestries: one for K. lactis and its relatives, one for K. phaffii, and one for the remaining species. The monophyletic and distinctive nature of the group comprising K. lactis and its relatives, as revealed by the rRNA phylogeny, is corroborated by information from other sources. This group represents a separate genus, and its proper genus name is Zygofabospora Kudriavzev. K. phaffii may be a separate genus or a member of another genus not included in this thesis. The rest of Kluyveromyces species share a common ancestry with Saccharomyces, Torulaspora, and Zygosaccharomyces. A single genus including all descendants of this ancestry is too heterogeneous. In relation to Saccharomyces, Torulaspora, and Zygosaccharomyces, the monophyletic group consisting of K. thermotolerans, K. waltii, and S. kluyeri is distinct and should be considered to represent another genus. The other species, related to either Saccharomyces, Torulaspora, or Zygosaccharomyces, should be retained in Kluyveromyces provisionally. This is because the distinction between Saccharomyces, Torulaspora, or Zygosaccharomyces by themselves is ambiguous, and no other evidence has been found to support the reclassification of these Kluyveromyces species into the three genera.



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