infections beer Ascomycota wine Yeasts bread Dry yeast Yeast colonies

Transcription

1 infections beer Ascomycota wine Yeasts bread Dry yeast Yeast colonies

2 1. Fungi form a monophyletic group. Fungi Ascomycota No motile cells *

3 Ascus = meiosporangium G. Wong

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5 Ascomycota

6 Ascomycetous yeasts Saccharomycotina yeast Taphrinomycotina

7 Taphrinomycotina Schizosaccharomyces

8 Taphrinomycotina, Schizosaccharomycetales Schizosaccharomyces, the fission yeasts, have been isolated from slime fluxes, honey and fruit*. Characteristics Several characters distinguished this yeast from the Saccharomycetales -including their method of cell division and cell wall polysaccharides. a. After nuclear division the cell elongates and a wall is produced between the daughter nuclei. The new wall material apparently originates from the area between the cell wall and plasma membrane abutting the original cell wall. It develops as an annulus with inward growth until the new daughter cells are completely partitioned. Parts of the developing wall thicken during their formation, and eventually separate in a middle translucent layer leaving scars at the ends of the new cells. b. Cell of glucans and mannan, usually no chitin * Traditional African beers are made from various kinds of millet, sorghum, corn (i.e., maize), or plantains. Some of the names of these traditional beers are: Pombe (Eastern Africa); Dolo, Burukutu, Pito, Shukutu, and Tchakpalo (Western Africa); Bouza (Egypt, Ethiopia); and Merisa (Sudan).

9 Schizosaccharomyces Fission Yeast

10 Sporulation in the fission yeast Schizosaccharomyces pombe is a unique process in which the plasma membrane of spores is formed de novo within the cytoplasm of mother cells.

11 Saccharomycotina Members of Saccharomycetales are important in the baking, brewing, distilling, and related industries including fuel ethanol production, as supplements to food, in the manufacture of riboflavin and citric acid, as plant pathogens and mycoparasites, in the contamination and spoilage of foods, as human pathogens, as important components of ecosystems, and as model organisms for scientific study. In Saccharomyces budding is initiated at the time of duplication of the spindle pole body. An area of enzymatic wall softening within a newly developed chitinous ring allows a portion of the cell contents surrounded by newly synthesized wall to push out through the constricting ring. At the time nuclear division is almost complete, an abscission plate begins to form. This plate consists of a thin layer of chitin secreted at the invaginated plasma membrane of the separating cells. Separation of the bud from the mother cell then takes place and a bud scar is evident on the mother cell opposite the birth scar of the daughter cell. The bud scar resembles a crater on the surface of the mother cell with a raised circular rim with a punctation in the middle. By counting the bud scars on a cell, one can determine the number of buds that have been produced from it. Sometimes a succession of buds may be formed before each bud separates from the parent cell and the chain of buds is the pseudomycelium. The cell wall proper is composed mostly of 1-3- glucans, surface layer mannoproteins.

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14 Life cycle of S. cerevisiae, an example of a species that may have both haploid and diploid budding stages Heterothallic, with two of the ascospores in each ascus carrying one mating type (a) and two, the other mating type (α) After cell fusion, the zygotes begin to bud and several generations of diploid cells ensue before ascospore formation occurs One to four globose, smooth-walled ascospores are formed Pseudomycelium may be formed on occasion

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16 Single cells, pseudohyphae and hyphae Yeast - Candida At 37 degrees C, which happens to be 98.6 F, body temperature, the insidious Candida grows hyphae that burrow into its food source (you). FIGURE 73-1 Dimorphism in C albicans. DYC, Daughter yeast cell; GT, germ tube; H, hypha; Ph, pseudohypha; YMC, yeast mother cell. (X8,980)