6. Microorganisms: fungi Flashcards
What are the two types of moulds?
- Plasmodial slime moulds
- Cellular slime moulds
What are the two types of yeast?
- Budding yeast
- Fission yeast
What are the types of fungi?
Fungi grow as yeast / filamentous fungi:
- Yeast
- Filamentous fungi
Slime moulds previously classified as fungi but not anymore after genome sequencing
Explain slime moulds
Slime moulds - several kinds of unrelated eukaryotic organisms - life cycle includes a free-living single-celled stage and the formation of spores
What is the difference between cellular and plasmodial slime moulds?
Plasmodial slime moulds - form a single-celled (one giant cell) form fusion, multinucleate mass
Cellular slime molds (“social amoebae”) - form an aggregated mass of separate amoebas that are able to migrate as a unified whole, differentiate into spore bearing structures
How can cellular extension be induced in amoeba?
By providing cyclic AMP (cAMP) - amoeba have receptors - chemotaxis
What is the structure of yeast cells?
What is the difference between budding and fission yeast?
Different modes of preproduction:
- Budding yeast - parent cell creates an outgrowth that eventually becomes a daughter cell
- Fission yeast - parent cell reproduces by splitting in half
Give the latin name of a budding yeast
Saccharomyces cerevisiae
Give the latin name of a fission yeast
Saccharomyces pombe
Explain what are filamentous fungi
Filamentous fungi - producers of a wealth of secondary metabolites with various biological activities
Filamentous fungi grow by apical extension of their filaments, known as hyphae - hyphal growth can occur with / without cell-wall separation of cellular compartments, which is known as septation
How do hyphae grow?
Tip growth - apical extension: polarised extension that increases cell length
What cells exhibit tip growth?
- Fungal hyphae
- Pollen tubes
- Root hairs
- Algal and ferm rhizoids
- Moss cell filaments
Explain the cell structure of a fungal hypha
What are fungal spores? How are they spread?
Fungal spores - microscopic biological particles that allow fungi to be reproduced
Fungal spores spread: so small + lightweight - can easily move unseen in the air currents, and most fungal spores are spread by the wind
What is fungal spore germination?
Germination - the mechanism that under favourable conditions converts the spore from a dormant biological organism to one that grows vegetatively and is capable of either sexual / asexual reproduction
Germ tubes - specialised hyphae emerge during spore germination
Some spores are able to germinate after extended periods and extreme conditions (freezing temp, vacuum, electron beam / radiation)
What is a mycelium?
Mycelium are fungi’s vegetative structures composed of white or cream-colored long threads called hyphae
Mycellium a 3D network - in agar spread in 3D not only on the surface
What is a rhizomorphic mycelium?
Rhizomorphic mycelium - thick strands of hyphae which have adhered - helps fungus cover area, grow quickly through substrates and establish a feeding network
What is the apical body / apical vesicle cluster?
Hyphal tip - has apical body which contains apical vesicles, mcirovesicles, ribosomes, actin and microtubules
Also called Spiztenkorper
New apical body forms at the site of new branch formation
What happens if hyphae experience stress?
- Cessation of growth / retraction of apical body
- Hypha burst - spores burst - due to osmotic stress
What are hyphal septa?
Hyphal septa - cross walls with pores - allow passage of organelles and cytoplasm between adjacent hyphal compartments - septal pores can be blocked if hyphae are damaged
Septum formation compartmentalises hyphae and governs cytoplasmic flow - provides damage limitation mechanism in mechanical injuries
What is phototoxicity?
**Phototoxicity **- live cells stained with fluorescence - exposed to intensee light - can result in cell death - mitochondria turn off - potentially due to the loss of membrane potential
What is different about Golgi in filamentous fungi?
Golgi in filamentous fungi don’t form stacks as in animal, plant cells - Golgi donuts
How are the nuclei arranged in fungal hyphae?
Fungal hyphae are multinucleate - nuclei and other organelles pass through open septal pores
Usually nuclei divide synchonously in different hyphae - directional waves of nuclear division
Regions of hyphal extension usually without nuclei
Many nuclei needed -> spore production
Explain hyphal fusion
Hyphal fusion - hyphal branches grow towards each other in older parts of fungal colony
Occurs during colony establishment by germinating spores + during the formation of cross connections within mature mycelial colonies - for improving the chances of colony establishment by allowing heterogeneously distributed nutrients / water within the environment to be shared - cytoplasmic flow
Developed new technique - differential staining of colonies allows to observe hyphal fusion and cytoplasmic flow
What is the model organism for studying fungal mycelium?
Neurospora crassa
Examples of cell signalling mechanisms in growth of slime moulds, yeast and filamentous fungi
Slime molds, yeast, filamentous fungi - use diff signaling mechanisms to regulate their growth and development:
- Slime molds: extracellular signalling molecules (ex: cAMP) - coordinate their multicellular development
- Yeast: signaling pathways to regulate growth and response to environment (ex:. MAPK pathway, TOR pathway)
- Filamentous fungi: several signaling pathways to coordinate their growth and development (ex:. cAMP-PKA pathway)
What is the process of insect pathogenesis from fungi?
What are the fungal parasites of nematode worms?
Nematrophs - parasites of nematode worms - adhesive knobs - nematodes trapped by specialised hyphae and adhesive knobs
What are the human mycoses?
Only ~600 fungi are known to infect humans - disease - mycoses
Pathogenic fungi - opportunistic, cause mild symptoms in healthy adults
Human mycoses (fungal diseases):
- Dermatophytes
- Commensals
- Opportunistic pathogens of the lungs
- Opportunistic pathogens of wounds and traumatised tissues
- Naturally live in lungs
Explain dermatophytes
Dermatophytes - human mycoses of pathogenic fungi:
- superficial mycoses
- grow on dead, keratinised tissue of skin, hair, nails - use keratin as sole carbon and E source because produce keratinases
- cause ringworm, athlete’s foot, nail infections
- Reproduce asexual spores - conidia
- Hyphae can develop structures which aid infection - “perforating organ”
Explain commensal fungi
Commensals - grow harmlessly on mucous membranes but can become invasive under particular conditions
Ex Candida albicans yeast:
- usually harmless in mucous membranes (mouth, gut, vulvo-vagina tract)
- dimorphic under appropriate conditions fungus changes from budding yeast to hyphal growth
- can become pathogenic - newborns can get thrush from the birth canal
Explain opportunistic fungal pathogens of the lungs
Opportunistic fungal pathogens of the lungs - normally found as saprotrophs but can grow in the lungs and invade other tissues of immunocrompromised
- Fungi usually in soil / plants / animal remains
- Don’t spread host-to-host
- Ex: black mould - Aspergillus fumigatus - spores developed on hyphae - conidia - airborne asexual spores
- Ex: Cryptococcus neoformans - infect central nervous system causing meningitis - cryptococcosis - fatal if untreated
Example of an opportunistic fungi infecting through wounds / traumatised tissues
Opportunistic fungi of wounds or traumatised tissues - Sporothrix brasiliensis - cause sporotrichosis - a subcutaneous (deep skin leayers, fat, muscle) fungal infection
What are the stages of systematic infection of Candida albicans?
What are the stages of systematic infection of Aspergillus fumigatus?
- Lung invasion: through ciliated epithelium lining of respiratory tract / through alveoli
- Cells of epithelium engulf conidia - not engulfed conidia enter alveoli where germinate and cause infection
- In healthy individuals conidia killed by host defences / in immunodeficient Aspergillus fumigatus can be fatal
What are the stages of systematic infection of Cryptococcus neoformans?
What are the pathogenicity factors of Cryptococcus neoformans?
Pathogenicity factors:
- grow in human body temp
- can grow in 5% CO2
- have a capsule - not as easily phagocytosed or killed
- melanin - protects against UV and active oxidants
What are the main antifungal compounds used to treat fungal diseases in humans?
Antifungal compounds:
- Azoles - inhibit ergosterol synthesis
- Polyene antibiotics - disrupts ion homeostasis in fungal cells
- Echinocandins - inhibit synthesis of beta (1,3)-glucan
- Flucytosine - inhibits DNA and protein synthesis
What are the uses of fungi?
- Fungal textiles: cell wall based on chitin instead of cellulose/keratin
- Medical products: can be made into absorbent pads for personal hygiene; medicinal compounds from fungi (not fully approved by Western medicine - ex Cordyceps, Trametes versicolor)
- Food: mycoprotein from fungi potential to solve global food crisis - sustainable
- Used to produce secondary metabolites - penicillin
- Mycotoxins: aflatoxin, coprine, muscimol, muscarine, amanitins, orellanin
- Psychedelic compounds: LSD, psilocybin
