2.1 Properties Of Yeast Flashcards
Different yeast budding types for growth
- multilateral budding (successive buds are formed on diff parts of the cell wall, i.e. Sacch.) 2. Bi-polar (at opposite ends of cell alternatively) 3. binary fission
Spore forming yeast
around 1/2 yeast genera for spores, although sl more resistant to heat and drying vs veg cells, they are not as effective for survival through adverse conditions as bacterial spores; more sophisticated growth cycle than would be possible by budding alone (asexual reprod.)
Ascus
with unicellular yeasts such a sep structure is not formed, spores are formed within the cell, which becomes the ascus sac.; occurs in vegetative cells, typically during the mating, or non asexual reproduction, process.
Hanseniaspora and its non spore forming equivalent, Kloeckera
fermentive yeast which grow by multilateral budding, although is not capable of producing such high concentrations of ethanol as sacc.; often dominant yeasts of early stages of natural fermentations of grape must
Kleuveromyces
non sacch, but forms spores in a different way; most spp ferment lactose, therefore Kl. spp are important in industrial alc. production as a by product of the dairy industry
Pichia
non fermentative and grows on sugars only in low aerobic conditions; however, some spp. produce ethanol aerobically and have been investigated for prod. of bio eth. from pentose of seaweed.; can grow during aerobic culture of distilling yeast, also in early stages of a dist fermentation before DO in wort has been exhausted, and the volatile flavor congeners will prod. unacceptable flavor in spirit
Hansenula
sim to Pichia but distinguished in lab by the ability 2 utilize nitrate as a source of N to grow (most like ammonia salts or amino acids). Some spp of Pichia and Hans. produce large amounts of ethyl acetate or IAA…important contributors to flavor of natural ferments of brandy and rum, but equally troublesome contaminants of both, or whisky if high ester profile is not welcomed.
Schizosaccharomyces
only sig yeast genus which grows by binary fission; principle ferm yeast of local E. African beers, a possible agent of the malo lactic fermentation of ciders, and wines, and often part of yeast flora of natural fermentations of molasses for dark rum.
Non immunological or genetic tests to distinguish strains of S. cer
- measurement of performance, flavor, prod, etc in a small scale fermentations is one possibility; however, that may require 1 wk or more, more rapid tests are preferred 2. API strips with a set of 19 different C compounds (20 left blank intentionally) 3. growth or not on galactose, a-methyl glucosidase, trehalose, etc can distinguish diff strains after 2 days incubation 4. filter disks impregnated with various antibiotics or other inhibitors, even after 24 hr incubation, zone of inhibition of a film of yeast spread on a plate of culture med is obvious.
- non sandwich immunofluorescence
- reagent is AB to contaminant/ yeast to be detected, coupled to a dye, this method is most effective since contaminants are most easily observed with a fluorescent dye excited by UV light, although that requires a microscope with quartz, not glass, lenses, and UV filters for eye protection. In a contaminated culture, only the contaminants fluoresce since only they are coated with fluorescent AB and the majority of the culture yeast remains dark.
Advantages/ disadvantages of sandwich method
Ad= only on fluorescent reagent is required for all the specific anti-contam ABs in use, and the fluorescence is enhanced by the number of sheep anti-rabbit AB molecules attached to each target cell. Disad= depends on an AG diff b/e contaminant and the culture yeast, so unlikely to work when contam is S. cer.
- sandwich immunofluorescence method
- Sandwich= More convenient method… a range of AB can be used, prepared by immunization of rabbits against commonly encountered yeasts or bacteria, but these are not coupled to fluoro chrome. Instead only a single fluorescent AB is prepared against the rabbit AB protein (must be prepared in diff animal, ie sheep). AB molecules are Y-shaped with the specific reaction sites at the ends of the 2 short arms. Since the whole rabbit AB molecule is rabbit protein, the AG which stimulated production of sheep anti rabbit AB, sheep AB can react with any part so several fluorescent molecules can attach
Immunological methods to distinguish strains of S. cer or other contaminants…
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Genetic methods to distinguish strains of S. cer or other contaminants: 1. mol% G+C
requires specialized lab equipment based on genetic structure of yeast; 1. simple test to determine the amount of guanine and cytosine in the DNA (mol% G+C) is widely used in taxonomy but can not be used for ID since many obviously diff yeasts happen to have same %, but if 2 apparently similar yeast isolates showed ver diff %G+C values, they could not be the same genus or species.
Genetic methods to distinguish strains of S. cer or other contaminants: 2. fingerprinting
- DNA fingerprinting is a more practicable method for ID. Nuleur (or more rarely mitochondrial) DNA is chopped by a restriction E which attacks a specific sequence of usually 6 DNA bases. So for a particular DNA, where and how oftern the particular seq occurs will provide a mixture of DNA fragments which are characteristic of the orig DNA molecule, and electrophoresis and staining will show characteristic pattern of lines. Typically unsuitable for ID of new isolate, but method is ideal for showing whether successive instances of yeast or bacterial contamination or same or different.
