ABSTRACT
Genera, families, and possibly orders of basidiomycetous yeasts can be defined by 25S rRNA homology and correlated phenotypic characters. The teleomorphic genera Filobasidium, Leucosporidium, and Rhodosporidium have greater than 96 relative binding percent (rb%) intrageneric 25S rRNA homology and significant intergeneric separation from each other and from Filobasidiella. The anamorphic genus Cryptococcus can be defined by morphology (monopolar budding), colony color, and greater than 75 rb% intrageneric homology; Vanrija is heterogeneous. Agaricostilbum (Phragmobasidiomycetes, Auriculariales), Hansenula (Ascomycotera, Endomycota), Tremella (Phragmobasidiomycetes, Tremellales), and Ustilago (Ustomycota, Ustilaginales) appear equally unrelated to the Cryptococcus, Filobasidiella, and Rhodosporidium spp. used as probes. The Filobasidiaceae and Sporidiaceae, Filobasidiales and Sporidiales, form coherent homology groups which appear to have undergone convergent 25S rRNA evolution, since their relatedness is much greater than that indicated by 5S rRNA homology. Ribosomal RNA homologies do not appear to measure evolutionary distance.
Subject(s)
Phylogeny , RNA, Fungal/genetics , RNA, Ribosomal/genetics , Sequence Homology, Nucleic Acid , Yeasts/classification , Biological Evolution , Phenotype , Yeasts/geneticsABSTRACT
In a new combination of techniques for ribosomal RNA hybridization, complementary DNA is synthesized on 25S ribosomal RNA fragments generated by mild alkali treatment, by the enzymatic addition of polyadenylic acid tails, hybridization of these tails with oligo deoxyribosylthymine, and reverse transcription in the presence of tritiated TTP. Hybridization reactions are performed in solution. Heteroduplexes are collected on diethylaminoethylcellulose filter discs after treatment with S1 nuclease. The problems presented by secondary rRNA structure are avoided by denaturation before reverse transcription and before hybridization. The high percentage of duplex formation (78-87%), the low standard deviation of relative binding (averaging +/- 1.30% relative binding), and small differences in reciprocal hybridizations (1.71-5.18% relative binding), as well as the elimination of complications resulting from differences in the number of rRNA cistrons in nuclear DNA, make this method preferable to the membrane-filter technique commonly used in phylogenetic classifications based on the homology of large rRNAs.
Subject(s)
DNA/genetics , Nucleic Acid Hybridization , Phylogeny , RNA, Ribosomal/genetics , DNA, Fungal/genetics , Genes , Methods , Nucleic Acid Denaturation , Nucleic Acid Heteroduplexes , RNA, Fungal/genetics , Yeasts/geneticsABSTRACT
A primary fixative containing glutaraldehyde (3%), acrolein (1.5%), and paraformaldehyde (1.5%) buffered in 0.05 M sodium cacodylate at pH 7.2 was applied to the cells Cryptococcus vishniacii for 2 hours on ice. The cells were then treated with a 6% aqueous solution of potassium permanganate for 1 hour at room temperature. This method preserves most of the yeast cell fine structural components including cell walls and membrane, nuclear membrane, mitochondria, endoplasmic reticula, microbodies, vacuoles, nucleoli, and ribosomes. However, it leads to disruption of capsular materials and loss of some of the lipid and glycogen granules.
Subject(s)
Cryptococcus/ultrastructure , Microbiological Techniques , Acrolein , Cell Membrane/ultrastructure , Cell Wall/ultrastructure , Cytoplasmic Granules/ultrastructure , Fixatives , Formaldehyde , Glutaral , Microscopy, Electron , Organoids/ultrastructure , Polymers , Potassium PermanganateABSTRACT
The DNA base compositions and photoreactivable sectors of six species of Hansenula were determined. The G+C ratios revealed two groups; the first had values of 38 to 44% and the second had lower values of 32-36%. Hansenula muscicola could not repair the UV-induced damage; whereas, H. dryadoides, H. lynferdii, H. ofunaensis, H. philodendra, and H. syndowiorum could do so.