MYCOLOGY (MIC 206)

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MYCOLOGY (MIC 206)

• CHAPTER 2
• REPRODUCTION

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Reproduction

• Filamentous fungi
• Asexually by fragmentation of hyphae
• Asexual and sexual reproduction by spores
• Yeasts
• Asexually by budding or fission
• Fission e.g. Schizosacchromyces pombe.
• Budding e.g. Saccharomyces cerevisiae.
• Sexual reproduction by spores (in high stress
  condition)

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Terms

• Fragmentation can occur whereby mycelium are torn
  apart by external forces and these bits can start
  new individuals if conditions are favourable.
• Fission is a simple splitting of a cell into two
  new daughter cells by constriction and the
  formation of a cell wall e.g. yeast.
• Budding is the production of small outgrowths
  (bud) from a parent cell and as the bus is
  formed, the nucleus of the parent cell divides
  and one daughter nucleus migrates into the bud.
  The bud increase in size while still attached to
  the parent cell and eventually breaks off and
  forms a new individual. Yeast reproduce via
  budding but do some other fungi in different
  conditions.

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Reproduction

• Telomorphs-produce both sexual and asexual spores
• Anamorphs- lost ability to reproduce
  sexually-Penicillium
• belonged to Deuteromycota
• now classified as anamorphs of other phyla rRNA
  Woese
• most are Ascomycetes

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Asexual Spores

• More important type of reproduction as it occurs
  several times throughout the season.
• Produced by fragmentation of aerial hyphae
• Progeny genetically identical to parent

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• Production of spores is most common type of
  reproduction.
• Production of spores where each spore germinate
  to form a germ tube that grows into the mycelium.
• Spores can be of various colours, depending on
• the colour of hyaline (green, yellow, orange,
  red, brown, black)
• shape (oval, oblong, needle-shaped, helical)
• number of cells (one to many)
• arrangement of cells and where they are situated.

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• Several types of spores
• Conidiospores
• Blastospores
• Chlamydospores
• Sporangiospores
• Arthrospores

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Arthrospores
1A
2
Chlamydospores
1
Conidiospores
3
1B
Blastospores
Sporangiospores
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ASEXUAL SPORES

• Conidiospore
• Multiple (chains) or single spores formed at the
  end of an aerial hypha
• Not enclosed within a sac
• Eg Aspergillus spp. and Penicillium spp.

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Conidial fungus

• reproduces by means of asexual spores called
  conidia
• Conidia vary greatly in shape, size and color
• Most of the common household molds mildews are
  conidial fungi

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ASEXUAL SPORES (cont.)

• Blastospores
• A bud coming off the parent cell
• Candida albicans

Blastospore
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ASEXUAL SPORES (cont.)

• Chlamydospore
• Formed within hypha
• Thick-walled spore
• Candida albicans

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Chlamydospores

• The chlamydospore is a method of producing a
  substantial resting spore very quickly
• Nutrient is shunted from adjacent cells into a
  preferred cell and it swells up, converts
  nutrient materials to oil droplets for efficient
  storage, then rounds off with a thick, often
  roughened outer wall for protection

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ASEXUAL SPORES (cont.)

• Sporangiospores
• Hundreds formed within a sac (sporangium) at the
  end of an aerial hypha
• Rhizopus spp.

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Sexual Reproduction

• Union of two nuclei.
• The entire thallus can be converted into one or
  more reproductive structures.
• Somatic and reproductive phases do not occur
  together in the same individual and this is
  called holocarpic.
• In majority of fungi, only a portion of the
  thallus give rise to reproductive organs and they
  are called eucarpic.

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Sexual Reproduction (cont)

• Some fungal species produce distinguishable male
  and female sex organs on each thallus
  hermaphroditic or monoecius. These species can
  reproduce sexually by itself.
• Other species consist of male or female thalli
  dioecious and therefore cannot reproduce itself.

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• The sex organs are called gametangia /
  gametangium which may differentiate into gametes.
  
• The male gametangium are called antheridia /
  antheridium and the female are called oogonia /
  oogonium.
• Heterokaryosis the existence of different kinds
  of nuclei in the same individual.

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Sexual Spores

• Three phases of development
• Plasmogamy a union of two protoplasts bringing
  about the nuclei close together and within same
  cell.
• - haploid nucleus of a donor cell () penetrates
  the
• cytoplasm of a recipient cell (-)
• Karyogamy Fusion of the two nuclei. Formation
  of a dikaryon a binucleate cell containing two
  nuclei from each parent
• - the 2 nuclei fuse to form a diploid nucleus
• Meiosis diploid nucleus gives rise to haploid
  nuclei
• - Sexual spores, some , some -,some
  recombinants
• - Sexual spores used to classify fungi into
  divisions

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Classification of these groups

• First three groups is based on their method of
  sexual reproduction
• 4th group, the Deuteromycetes, have NO sexual
  reproduction

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Zygomycota (Conjugation Fungi)

• Also known as bread molds.
• Saprophytic molds with coenocytic hyphae (lack
  septa).
• Asexual Reproduction Used most of the time.
• Sporangiospore Asexual spore enclosed within a
  sporangium or sac at the end on an aerial hypha.
• Sexual Reproduction Occurs through conjugation,
  the joining of hypha of two different strains
  (plus and minus).
• Zygospores Sexual spores which are enclosed in
  a thick, resistant wall.
• Generally not pathogens.
• Rhizopus stolonifer Common black bread mold.
  May cause opportunistic infections in diabetes
  patients

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Life Cycle of a Zygomycete Black Bread Mold
(Rhizopus)Reproduces Asexually and Sexually
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Reproductive Structures of Zygomycete
(Rhizopus)Sporangia (asexual) and Zygospore
(sexual)
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Ascomycota (Sac Fungi)

• Molds with septate hyphae and some yeasts.
• Asexual Reproduction Conidiospores not enclosed
  in a sac. Become airborne easily. Form chains
  (broom-like structures).
• Sexual Reproduction Ascospores enclosed in a
  sac-like structure (ascus).
• Include common antibiotic producing fungi and
  yeasts, and several human pathogens.
• Penicillium notatum (Produces penicillin)
• Saccharomyces (Brewers yeast)
• Trychophyton (Athletes foot)
• Aspergillus (Carcinogenic aflatoxin in peanuts),

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Life Cycle of Eupenicillium (Ascomycete)Reproduce
s Asexually and Sexually
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Basidiomycota (Club Fungi)

• Have septate hyphae.
• Include mushrooms, toadstools, rusts, and smuts.
• Sexual Reproduction Produce basidiospores
  Spores formed externally on a club shaped sexual
  structure or base called basidium.
• Asexual Reproduction Through hyphae.
• Examples
• Amanita Mushroom produces lethal toxins to
  humans.
• Claviceps purpurea Produces ergot toxin in wheat
  and rye.

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Life Cycle of a BasidiomyceteMushrooms are
Produced Sexually
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Deuteromycota

• Not known to produce sexual spores.
• Reproduce asexually.
• Catch-all category for unclassified fungi
• Pneumocystis carinii Causes pneumonia in AIDS
  patients. Leading cause of death in AIDS
  patients. Originally classified as a protozoan.
• Candida albicans Causes yeast infections of
  vagina in women. Opportunistic infections of
  mucous membranes in AIDS patients.

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A. Aspergillus B. Penicillium C. Geotrichum D.
Trichophyton E. Microsporum F. Epidermophyton
and G. Rhizopus.  From Medical Microbiology,
1990, Murray, et al., p. 300, Fig. 28-2.
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Parasexual Reproduction

• This phenomenon occurs whereby the three steps in
  sexual reproduction take place not at specific
  points in the life cycle.
• Several Ascomycota species are not known to have
  a sexual cycle. Such asexual species may be able
  to undergo genetic recombination between
  individuals by processes involving heterokaryosis
  and parasexual events.
• Parasexuality refers to the process of
  heterokaryosis, caused by merging of two hyphae
  belonging to different individuals, by a process
  called anastomosis, followed by a series of
  events resulting in genetically different cell
  nuclei in the mycelium.

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QUESTIONS

1. Differentiate between the types of spores.
2. Differentiate between the different types of
   asexual reproduction.
3. Name one (1) fungus that has a parasexual type of
   reproduction.