mycology (mic 206) chapter 2: reproduction. reproduction filamentous fungi – asexually by...

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)

TermsFragmentation 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 sexually-Penicillium– 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:

ConidiosporesBlastosporesChlamydosporesSporangiosporesArthrospores

Chlamydospores

Arthrospores

Sporangiospores

Conidiospores

Blastospores

1

3

1A

1B

2

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

• Sporangiospores– Hundreds formed within a sac

(sporangium) at the end of an aerial hypha

– Rhizopus spp.

ASEXUAL SPORES (cont.)

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.

• 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.

Sexual Reproduction (con’t)

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

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

Zygomycota (Conjugation Fungi)

Life Cycle of a Zygomycete: Black Bread Mold (Rhizopus)

Reproduces Asexually and Sexually

Reproductive Structures of Zygomycete (Rhizopus)Sporangia (asexual) and Zygospore (sexual)

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),

Ascomycota (Sac Fungi)

Life Cycle of Eupenicillium (Ascomycete)Reproduces Asexually and Sexually

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.

Basidiomycota (Club Fungi)

Life Cycle of a BasidiomyceteMushrooms are Produced Sexually

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.

Deuteromycota

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.