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BIOL 121 - Impact Of Microbes > Fungi > Flashcards

Fungi Flashcards

1
Q

What are fungi

A

They represent a unique group of organisms which are extremely diverse with respect to their activities, shape and form

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2
Q

Defining characteristics of fungi (1)

A

Eukaryotes

Cell wall made of chitin and polysaccharides

Reproduction (sexually and asexually - nuclei are usually haploid)

Heterotrophs (obtaining energy by degrading complex organic molecules)
- contain no chlorophyll
- cannot utilise CO2 as a single carbon source
- cannot fix N2

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3
Q

Defining characteristics of fungi (2) - heterotrophs

A

Heterotrophs absorb nutrients from their environment and live as either:

  • Saprophytes (derive nutrients from dead remains)
  • Necrophytes (derive nutrients from organisms they have killed - parasitic)
  • Biotrophs (derive nutrients from living host - parasitic)

Successful heterotrophs:
- ability to use diverse range of C sources
- provided with suitable C and N sources - impressive array of bio-synthetic powers
- occupy a diverse array of ecological niches

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4
Q

Differences with fungi and plants

A

Plants are photoautotrophs. Fungi secrete enzymes and digest organic material

Plants are made up of ‘box-like’ cells. Fungi are usually ‘filamentous’ in form

Differences in the cell wall composition

Nuclear mitosis: fungi takes place within the nucleus. Other eukaryotes, nuclear envelope breaks down

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5
Q

Range of fungal growth forms:
: yeast

A

Eg Saccharomyces cerevisiae

  • single cell / single nucleus
  • oval or spherical
  • reproduces asexually by producing an identical but separate daughter cell
  • can aggregate to form a colony or ‘pseudohyphae’
  • 3-5 um diameter
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6
Q

Range of fungal growth forms: filamentous fungi (mold)

A
  • vast majority of fungi
  • multicellular
  • Long ‘thread-like’ filaments (hyphae)
  • polarised tip growth
  • mycelium (colony or mass of hyphae)
  • large complex bodies (interwoven mass of hyphae)
  • reproduce via spores
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7
Q

Range of fungal growth forms: dimorphism yeast / fungi

A
  • Environmental cues (eg temperature, CO2) trigger transition between yeast and filamentous forms
  • medically important
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8
Q

Reproduction in fungi: asexual
(Yeasts)

A
  • typically bud a daughter cell
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9
Q

Reproduction in fungi: asexual
(Filamentous fungi)

A
  • generate light weight spores for effective dispersion
  • colonise food supply rapidly
  • haploid
  • formed from specialised aerial extensions from mycelia
  • produces in many different species-specific ways
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10
Q

Reproduction in fungi: sexual

A
  • union of compatible nuclei to form diploid (2n) state
  • usually occurs when nutrients are in poor supply
  • sexual spores are usually more hardy structures allowing survival in adverse conditions
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11
Q

Reproduction in fungi: sexual
(Heterothallism)

A

Results in exchange of genetic material and requires two different mating types (+ , -)

(Don’t need to find opposite mating type, can still reproduce)

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12
Q

Reproduction in fungi: sexual (homothallism)

A

Some fungi are able to self-fertilise and produce sexual spores

Spores are more likely to survive in adverse conditions than if produced asexually.

(Don’t need to find opposite mating type, can still reproduce)

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13
Q

Three major divisions (phyla) of fungi

A

Zygomycota (zygomycetes) (1000 species number)

Ascomycota (Ascomycetes) (65,000 species number)

Basidomycota (basidiomycetes) (30,000 species number)

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14
Q

Zygomycetes

(Refer to slide 16-18 L8 for reproduction information)

A

Aseptate hyphae (haploid)

Smallest phyla

Asexual features: haploid sporangiospores from sporangia

Sexual features: diploid zygospore

Most are saprophytes (eg Rhizopus stolonifer)

Contains Glomus spp - important mycorrhizal fungi

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15
Q

Ascomycetes

(Refer to slide 19-21 L8 for reproduction information)

A
  • Septate hyphae (haploid)
  • asexual features: haploid conidospores from conidiophores
  • sexual features: haploid ascospores (meiosis followed by mitosis)
  • most are saprophytes
  • model organisms (eg Aspergillus nidulans)
  • many important plant pathogens (eg Calviceps)
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16
Q

Basidomycetes

(Refer to slide 22-24 L8 for reproduction information)

A

Septate hyphae (dikaryons)

Asexual cycle is uncommon

Sexual features: haploid basidiospores (meiosis)

Various types of fruiting body (basidiocarps) - can be a food source (eg Agaricus bisporus fruiting bodies)

Most are saprophytes (eg Serpula lacrymans)

Many important plant pathogens (eg rusts; Puccinia spp)

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17
Q

Deuteromycetes

A

Sexual reproduction cycle absent

Asexual spores formed in various ways (eg conidiophores & arthroconidia)

Fungi imperfect

Most were Ascomycetes and did include the important food spoiler and the industrial workhorse (Aspergillus flavin and Aspergillus niger)

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18
Q

Fungi of medical importance

A

Mycoses
Allergies
Mycotoxins

19
Q

Fungi as phytopathogens

A

Primary cause of disease in plants - effects crop efficiency in plants (agricultural effects)

20
Q

What are true pathogens

A

Healthy host

Adapted to high temperature and low oxygen tension

Restricted to specific geographical regions

Display thermal dimorphism
(Slide 6 L9)

Usually asymptomatic in healthy host

Not obligate parasites (have a saprophytic lifestyle)

21
Q

Examples of true pathogens

A

Histoplasmosis (Histoplasma capsulatum)
Most common
500,000 cases per year in USA

Eg causes pneumonia

Another example: Coccidioidomycosis (Coccidioides immitis)

22
Q

Opportunistic pathogens

A

Host defences need to be impaired (immunocompromised host)

Distributed world-wide

Many species and genera / increasing all the time

Show no specific adaptations to the host environment but are hardy to it (can tolerate)

Superficial / benign to chronic systemic infections

Prognosis - poor (limited drug treatment, increasing mortality rate)

23
Q

Examples of opportunistic pathogens

A

Candida albicans infection
- widespread
- immunocompetent: non invasive
- immunocompromised: systemic causing organ failure
- most common fungal pathogen causing loss of life
- fourth biggest killer in tertiary care hospitals
- invades wounds / burns
- dimorphism yeast - hyphae form is aggressive

Another example: Aspergillosis

24
Q

Dermatophytes (skin plants)

A

Superficial infections in healthy host (just discomfort, not disease)

World-wide distribution

Most common cause ringworm and a theme yes food

Not life threatening

Feeds off of Keratin

25
Q

Phytopathogenic fungi major groups

A

Pathogens of immature (or compromised) tissue

Pathogens of mature and non-compromised tissue
- Necrotrophic pathogens (kills plant)
- Biotrophic pathogens (infects plant but plant doesn’t realise)

26
Q

Pathogens of immature tissue

A

Broad host range (not species specific)
Soil-borne pathogens stack roots
Aggressive invasion of root tips with extensive destruction
Water-logged soils

27
Q

Pathogens of mature tissue

A

Usually high degree of host specificity (fungus evolved to attack the host - specific relationship)

Necrotrophic pathogens
- excrete toxins and cell wall digesting enzymes
- host cell death
- tissue invasion
- evoke host resistance mechanism (plant tries to counter the attack)

28
Q

Pathogens of mature tissue: biotrophic pathogens

A

Maintain host viability (doesn’t kill just compromises)

Limited tissue invasion

Do not evoke resistance mechanisms

Life cycle depends on living host

Arrive as spores on leaves

29
Q

Biotrophic pathogens - the haustorial biotrophs

A

Not broken into the cell, other than cell wall. Becomes a nutrient sink (depletes plant of nutrients). No resistance mechanism triggered

Eg Puccinia graminis
Via stomat opening, infect mesophyll cells

Eg Erysiphe graminis
Infect directly through cuticle
Epidermal layer

30
Q

Fungi have been used as biological control agents for what?

A

Insect pests - most effective in glasshouses

Phytopathogenic fungi - most effective in soil

31
Q

Typical infection style: fungi control insect pests

A

Spore attachment

Germination to intersegmental region

Penetration of cuticle (infection peg: lipases; chitinase; proteases)

Hyphal invasion beneath cuticle

Sporulates

Proliferation into blood (yeast phase)

Death (toxins/sugar levels)

Saprophytic stage (spores)

32
Q

example of fungi as insect control: Verticillium lecanii

A

Produces sports in liquid fermentors (fast)

Fresh pores are sticky so attach to insect which is contagious

Spores don’t need to be ingested

Germination needs a high humidity >95%, at constant temp of 15-18°C for 12 hours

33
Q

Fungi to control Phytopathogenic fungi: mechanisms of control

A

Parasitism of pathogen by BCA

Production of antibiotics, BCA poisons the pathogen

Competition for nutrients, water, space

34
Q

Fungi to control Phytopathogenic fungi: parasitism

A

Fungi that parasitise other fungi - ‘mycoparasites’ (many are Zygomycetes which are Biotrophic and produce haustoria)

Most potential shown by Necrotrophic mycoparasites: eg Pythium oligandrum (oomycete)

35
Q

Fungi to control Phytopathogenic fungi: production of antibiotics

A

For example Trichoderma spp. produce antibiotics

36
Q

Fungi to control Phytopathogenic fungi: competition

A

For example control of ‘butt rot’ in conifers

37
Q

Fungi in food and drink: yeast

A

Saccharomyces cerevisiae
Is used in baking and brewing (yeast)

Converts C6H12O6 into 2C2H5OH + 2CO2

Saccharomyces cerevisiae is then used in yeast extract paste - or marmite.

38
Q

Fungi in food and drink: soya bean products

A

Soya bean: Positive and negatives - difficult for us to digest so it’s fermented so we can eat it.

It’s fermented with Aspergillus oryzae

39
Q

Enzymes produced commercially by Aspergillus niger include

A

Glucoamylases (liquid starch to hight glucose syrup)

Pectinases (breakdown pectins in plant cell walls - fruit juices)

Glucose oxidase (food preservation; diagnostic tests)

Phytases (improvement of animal feed)

40
Q

What’s the problem with enzymes produced commercially by Aspergillus niger

A

Starch based foods cooked at high temperatures recently discovered high levels of acrylamide (carcinogen)

41
Q

Fungal cell factories: drugs

Antibiotics: penecillin
(Penicillium notatum)

A

Antibiotics: penecillin
(Penicillium notatum)

1928 - Alexander Fleming
Developed by Howard Florey and Ernst Chain (Oxford)
1941 - first life saved and widely used by end of WW2
Improved yields from 2mg to 30g
Chemically altered semi-synthetic penicillins (methicillin; ampicillin)

42
Q

Fungal cell factories: drugs

Statins

A

High plasma cholesterol levels is an important risk factor in coronary heart disease

Most of the body’s cholesterol is synthesised directly from intracellular pre-cursors.

Statins are fungal metabolites that inhibit the biosynthesis of cholesterol and are used to reduce plasma cholesterol levels

43
Q

Which fungi show potential as biological control agents

A

Verticillium lecanii

Trichoderma spp.

BIOL 121 - Impact Of Microbes (4 decks)

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