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Title: Molecular systematics of the genera Cryptococcus and Filobasidiella
Author: Sivakumaran, Swarna.
Awarding Body: Birkbeck (University of London)
Current Institution: Birkbeck (University of London)
Date of Award: 2004
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A molecular systematic study of the genera Cryptococcus and Filobasidiella was undertaken through PCR-RFLP and DNA sequence data analysis. The closely related genera in the orders Tremellales, Filobasidiales and Cystofilobasidiales included in the study were the anamorphic genera Trichosporon, Tsuchiyaea, Bullera and Fellomyces, together with the teleomorphic genera Tremella, Sirobasidium, Filobasidium and Cystofilobasidium. RFLP of PCR products was employed for an initial screening of the taxa to determine DNA variation. PCR-RFLP analysis of the ITS region in the ribosomal RNA gene cluster identified that Cryptococcus, Filobasidiella and other related taxa consisted of 64 groups or ITS-RFLP types. The DNA sequence data analyses were based on a multiple gene approach. Nuclear small subunit ribosomal DNA sequences (1682bp) and the ITS and 5.8S region of ribosomal DNA sequences (629bp) from 164 taxa were analysed using parasimony and Bayesian methods to show the ribosomal phylogeny of the genera Cryptococcus and Filobasidiella with other related taxa. As an additional gene region a defined section of the protein-encoding ,6-tubulin gene sequences (1147bp) from 76 taxa was analysed and compared with the ribosomal phylogeny. Combined analysis of the 18S and ITS ribosomal gene regions was also included, to support and strengthen the independent analysis. The results showed that in general there was a good agreement between the taxonomic relationships of the genera Filobasidiella and Cryptococcus with other related taxa based 3 on the ribosomal and ,3-tubulin phylogeny. All three analyses independently supported the positioning of the genus Filobasidiella within the Tremellales lineage and supported the monophyly of the genus Filobasidiella. The anamorphic genus Cryptococcus was shown to be an aggregate of several diverse taxa belonging to different genera. The present study provided sufficient evidence for determining the grouping of the Cryptococcus species and thus serves as a foundation for a new classification of this anamorphic genus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available