Transcript INTRODUCTION TO MYCOLOGY

MYCOLOGY
(MIC 206)
CHAPTER 2:
REPRODUCTION
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)
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.
Reproduction
• Telomorphs-produce both sexual and asexual
spores
• Anamorphs- lost ability to reproduce sexuallyPenicillium
– belonged to Deuteromycota
– now classified as anamorphs of other phyla: rRNA
& Woese
– most are Ascomycetes
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
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.
Several types of spores:
Conidiospores
Blastospores
Chlamydospores
Sporangiospores
Arthrospores
Arthrospores
1A
2
Chlamydospores
1
Conidiospores
3
Sporangiospores
1B
Blastospores
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.
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
ASEXUAL SPORES (cont.)
• Blastospores
– A bud coming off the parent cell
– Candida albicans
Blastospore
ASEXUAL SPORES (cont.)
• Chlamydospore
– Formed within hypha
– Thick-walled spore
• Candida albicans
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
ASEXUAL SPORES (cont.)
• Sporangiospores
– Hundreds formed within a sac
(sporangium) at the end of an aerial
hypha
– Rhizopus spp.
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.
Sexual Reproduction (con’t)
•
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.
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.
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
Classification of these groups
• First three groups is based on their
method of sexual reproduction
• 4th group, the Deuteromycetes, have NO
sexual reproduction
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
Life Cycle of a Zygomycete: Black Bread Mold (Rhizopus)
Reproduces Asexually and Sexually
Reproductive Structures of Zygomycete (Rhizopus)
Sporangia (asexual) and Zygospore (sexual)
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 (Brewer’s yeast)
– Trychophyton (Athlete’s foot)
– Aspergillus (Carcinogenic aflatoxin in peanuts),

Life Cycle of Eupenicillium (Ascomycete)
Reproduces Asexually and Sexually
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.
Life Cycle of a Basidiomycete
Mushrooms are Produced Sexually
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.
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.
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.
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.