Module 6 - Mycology Flashcards
What is the serial endosymbiosis theory, and how does it relate to the evolutionary relationship between fungi, animals, and plants?
The serial endosymbiosis theory suggests that eukaryotic cells evolved through a series of symbiotic mergers between different prokaryotic cells. Opisthokonts, a group within eukaryotes that includes animals and fungi, are characterized by cells that propel themselves with a single posterior flagellum. This theory, as clarified by Cavalier-Smith in 1987, proposed that fungi are more closely related to animals than to plants, changing the previous assumption that fungi were closely related to plants.
How do fungal cell walls differ from plant and bacterial cell walls?
Fungal cell walls contain mannans, glucans, and chitin. Plant cell walls contain xyloglucan, cellulose, and pectins. Bacterial cell walls contain peptidoglycan.
What are the common growth forms of fungi?
Yeast: Round to ovoid cells that separate readily from each other.
Pseudohyphae: Elongated, ellipsoid yeast cells that remain attached at a constricted septation site, often growing in a branching pattern.
True Hyphae: Characteristic of moulds, they are long, highly polarized cells with parallel sides and no constrictions between cells.
What is lignin and its role in plants?
Lignin is a heterogeneous polymer, second only to cellulose as the most abundant organic compound in the biosphere.
It provides structural rigidity to plants.
Lignin is highly resistant to degradation, making it a key component of plant durability.
What is Phanerochaete chrysosporium and its role in lignin degradation?
Phanerochaete chrysosporium is the best-studied white rot fungus.
It produces enzymes that generate reactive free radicals, catalyzing lignin depolymerization.
Key components of its lignin degradation system are manganese-dependent peroxidase and lignin peroxidase.
These enzymes are encoded by large gene families in the P. chrysosporium genome.
What does the comparison of 31 fungal genomes reveal about lignin-degrading peroxidases?
Lignin-degrading peroxidases expanded in a common ancestor of fungi.
This gene family expansion is estimated, using a molecular clock, to have occurred at the end of the Carboniferous Period.
What are the two main types of fungal/plant symbioses and how do they function?
Mycorrhiza: Fungal growth enlarges the root surface area, increasing the plant’s absorption of water and minerals. In return, the plant provides the fungus with sugars.
Lichens: The fungus helps absorb moisture from the air, while the algae partner performs photosynthesis to produce sugars for both organisms.
What are the characteristics and effects of Russula emetica, commonly known as “the sickener”?
It is a mycorrhizal species that associates with conifers.
Has a peppery taste.
Causes diarrhea and vomiting when consumed.
How does Russula persanguinea relate to Russula emetica?
Russula persanguinea is a closely related species found in Australia.
It associates with eucalyptus trees.
What is Amanita phalloides, and why is it known as the “death cap mushroom”?
Amanita phalloides belongs to a genus with 900–1,000 species, some of which are edible, but others, like A. phalloides, produce potent cyclic peptide toxins.
These toxins survive digestion and target liver cells by inhibiting RNA polymerase II.
Human LD₅₀ for α-amanitin is ~0.1 mg/kg, with 10–12 mg present in one mushroom.
Symptoms include gastrointestinal distress within 6–12 hours, temporary remission for 12–24 hours, followed by progressive liver failure, leading to death within 3–5 days.
What is Ustilago maydis and what unique characteristic does it have?
Ustilago maydis is a basidiomycete pathogen that infects maize.
During its sexual cycle, it forms tumors on the plant that are filled with black spores.
Interestingly, it is also considered a delicacy and “tastes awesome.”
What is the significance of the Fertile Crescent in early civilization?
Known as “The cradle of civilization,” it was a moist and fertile region compared to surrounding areas.
It was home to the eight Neolithic founder crops: Emmer, Einkorn, Barley, Flax, Chickpea, Pea, Lentil, and Bitter vetch.
Evidence shows that bread and beer production dates back approximately 8,000 years in this region.
What is the origin of the name Saccharomyces cerevisiae?
Derived from sakkharon, the Greek word for “sugar.”
Mykēs is Greek for “fungus.”
Cerevisia is Latin for “beer.”
What is yeast?
Yeast:
A frothy substance produced by fermentation of malt, etc. such as in the production of beer, often used for leavening in baking
A unicellular fungal growth form where the organism reproduces either by budding or fission
Saccharomyces cerevisiae, also known as budding yeast, baker’s yeast and brewer’s yeast
Two species of yeast used:
- Saccharomyces cerevisiae
- Saccharomyces carlsbergensis (syn. pastorianus)
Yeast Extract:
A processed yeast product commonly used in microbiological media
Vegemite
Why are fungi easy to work with?
- Easy to grow, short life cycles
- Small genome relative to other eukaryotes (only ~10-40 Mbp)
- Many fungal genes are homologous to those in other eukaryotes
- An extremely wide array of molecular techniques
- Most have haploid genomes amenable to mutation
- Sexual stage for analysis of segregation and recombination of genes; all products of meiosis can be retrieved in haploid spores
- Asexual (clonal) reproduction
What is Saccharomyces cerevisiae?
- Most well-known member of the phylum Ascomycota
- Cells are spherical to oval, cell division through budding
- 5-10 µM diameter
- Flourish in habitats where sugars are present
- Sexual reproduction process called mating
What is the lifecycle of S.cerevisiae?
- Stable as a haploid (n=16), stable as a diploid (2n=32)
- Exists primarily as a diploid, particularly in industry
- Sexual cycle begins readily, but completion requires special sporulation conditions
What are the key characteristics of the genome of Saccharomyces cerevisiae, including its chromosome count, orientation of genes, and notable features of Chromosome 1?
Saccharomyces cerevisiae has 16 chromosomes totaling 12 Mb. The orientation of genes is generally random, with ORFs transcribed in one direction typically not overlapping with those in the reverse direction. Chromosome 1 is one of the smallest at 230 kb (0.23 Mb).
What are the key points of Das Reinheitsgebot?
The German Beer Purity Law, established in 1516, allowed only water, barley, and hops as ingredients in beer. If other ingredients were used, the beer would be confiscated.
To avoid competition with bakers for wheat and rye, brewers could only use barley.
Hops were required as a preservative to prevent the use of other harmful ingredients.
The Vorläufiges Biergesetz (Provisional German Beer Law, 1993) now allows yeast, wheat malt, and cane sugar, but not unmalted barley.
What enzymes are involved in starch breakdown in barley and how do they function?
The major energy store in barley endosperm is starch, composed of branched amylopectin and linear amylose.
α-amylase acts at random locations along the starch chain, producing maltotriose and maltose.
β-amylase operates from the non-reducing end of the starch molecule, hydrolyzing the second α-1,4 glycosidic bond to cleave off maltose units one at a time.
What is wort and how is it prepared in the brewing process?
Wort is a nutrient-rich liquid produced during the brewing process.
The preparation begins by milling malted grain, which is then combined with water and heated in a process called mashing.
During mashing, enzymes such as amylases act to convert starches into sugars.
After mashing, the wort is separated from the spent grain through a process known as lautering.
Flower clusters of Humulus lupulus (hops) are added to the wort for preservation and to impart bitterness.
The wort solution is then boiled for up to two hours and subsequently filtered.
What is sourdough and what role do yeast and bacteria play in its fermentation process?
Sourdough is a symbiotic and stable culture of wild yeasts and bacteria created from a mixture of flour and water, often passed down for years.
Lactic Acid Bacteria (LAB), such as Lactobacillus sanfranciscensis, L. pontis, L. fermentum, and others, hydrolyze starch and convert sugars into lactic and acetic acids, creating a sour taste and acidifying the dough to a pH of approximately 3.8, which inhibits the growth of harmful microbes.
Acid-tolerant yeasts, like Candida humilis and C. krusei, help leaven the bread by metabolizing the byproducts of lactic acid fermentation into carbon dioxide and ethanol.
Saccharomyces cerevisiae (baker’s yeast) has less tolerance to acetic acid compared to other sourdough yeasts.
What is the Pasteur effect in yeast metabolism?
The Pasteur effect refers to the phenomenon where energy production from glucose is maximized in the presence of oxygen through the TCA cycle.
In contrast, less energy is produced through anaerobic fermentation, specifically the conversion of glucose to ethanol and carbon dioxide:
C6H12O6 -> 2CO2 + 2CH3 + 2CH3CH2OH
In most fungi, essential genes exist whose products require oxygen to function.
Saccharomyces spp. have adapted to acquire non-oxygen requiring variants via horizontal gene transfer from anaerobic bacteria.
How does horizontal gene transfer relate to pyrimidine biosynthesis in Saccharomyces species?
Pyrimidine biosynthesis requires dihydroorotate dehydrogenase, a protein located in the mitochondria of eukaryotes that depends on oxygen.
Anaerobic bacterial species possess a cytoplasmic version of this enzyme that does not require oxygen.
Saccharomyces species have acquired the anaerobic bacterial version through horizontal gene transfer, allowing them to synthesize pyrimidines in oxygen-limited environments.
