biology of fungi - academics | kansas state...

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Biology of FUNgi

Lecture 10Basidiomycetes I

You Should Know...• Ascomycetes - three groups

– Archiascomycetes

– Saccharomycetales

– Filamentous ascomycetes

• Cleistothecial ascomycetes.

• Perithecial acomycetes.

• Apothecial ascomycetes.

• Plus examples of them all.

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Fungus of the day -Agaricus bisporus

Taxonomy: Phylum (subphylum) Basidiomycota Order - Agaricales Family - Agariceae

Agaricales - the family for gilledmushrooms.

Agaricus means gilled mushroom.

Bisporus - two spores per basidium.

Most mushrooms have 4 haploid productsof meiosis (basidiospores).

Agaricus bisporus

Basidium

Basidiospore

Sterigma

This is a typical basidiumwith 4 spores


What makes Agaricus into Agaricus?

Typical member of Agaricales:

A cap - Pileus

A stalk - Stipe

A neck ring - Annulus

Gills - lamellae - pink

Basidiospores - chocolate brown

Agaricus bisporus

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A. bisporus is the button mushroom thatyou buy at Dillon’s or eat on your pizza.

Most commonly cultivated - makes 90% ofthe mushroom production in the US (worthca $800 million annually)

Per capita consumption ca 2.2 lbs perannum.

Globally only 40% of the mushroomproduction


Cap color can be highly variable.

Button mushroom, crimini andPortobello are all the same species butnames have been given to the strainshelping distinguish between moremature and flavorful variants ordifferent colored caps

Three specimens of the same species -Agaricus bisporus

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A. bisporus is a secondary decomposer -other fungi and bacteria must do the initialwork.

Composting of the substrate required forbutton mushroom beds.

The compost bed is made of wheat strawand horse poop, other ingredients may beadded as well.

Composting beds make aselective medium to reducecompetition.


Phase I composting to modifysubstrate

Phase II composting afterpartial sterilization - selectivefor bacterial decomposers

Agaricus bisporus spawn

Spawn is added to trays andincubated at ca 24C

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Agaricus bisporus primordia...

And voilá - button mushrooms...

… turn into Agaricus bisporus basidiocarps...

Mushroom cultivation is among the top threebiotechnology industries.

Mushrooms make a great dietary supplement, lowfat, no cholesterol but a good source of protein anddietary fiber.

Agaricus bisporus

Quorn - mycoprotein as an examplefor fungal nutritional value


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A look forward...

• Basidiomycetes - defined.

• Generalized life.

• Holobasidiomycetes vs.heterobasidiomycetes

Reminder where we stand...

Ancestral traitsChitin GlycogenPosterior flagellum

Loss of phagotrophy

Loss of flagella

Dikaryotic stageSeptate mycelium

Ascospores

BasidiosporesDollipore septumClamp connections

Chytridiomycota

Basidiomycota

Ascomycota

Zygomycota

Animalia

?

?

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Basidium and basidiospores

General characteristics ofbasidiomycetes

As indicated by the phylum name,basidiomycetes share basidiosporeproduction in basidia. An additionalgood character is the presence of thedolipore septum.

Different septal structuresin higher fungi

Basidium

Basidiospore

Sterigma

General characteristics of basidiomycetes

Dolipore septum seems like a complex deviseto allow cytoplasmic streaming between thecompartments (cells) in the hyphae.

Dolipore septum is comprised of the central poreand the septal pore cap (above).

Dolipore septum

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Clamp connections

General characteristics ofbasidiomycetes

An additional oddity is the presence ofthe clamp connections.

Let’s take a look.

Clamp connections are the lumps that aretypical to some basidiomycetes.

Formation of clamp connections


Clamp connections exist to ensure that thedikaryophase is maintained through celldivisions.

The binucleate cell produces a branch intowhich one of the nuclei migrates. The twoparent nuclei go through a conjugate mitoticdivision. The sister nuclei separate as theseptum develops between the branch as well asthe new cell and the old and the new cells.The branch or the hook fuses with the old celland delivers one of the sister nuclei.

This way, each cell maintains the vegetativebinucleate dikaryophase.

Formation of clam connections and thenuclear behaviour during the celldivision

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Holo vs. heterobasidiomycetes


Basidia can take different shapes and forms.There are two different types of basidia whichwere considered as major divisions within thebasidiomycetes - holo- and heterobasidia.

Holobasidiomycete basidium is a single,usually club-shaped cell with most oftenfour sterigmata. Heterobasidiomycetebasidium divided into often four cells.

With all these characteristics in mind, let’s look at the classification aspect of thebasidiomycetes: three main groups within basidiomycota - hymenomycetes, smutsand rusts.

Basidiomycetes - divided into 3 groups

Primitive basidiomycetes

Smuts

Rusts

Basidiomycetous macromycetes

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Basidium development

Basidiospores develop at the tips ofsterigmata. The basidium developsfrom the terminal end of a binucleate,heterokaryotic hyphae - the dikaryon.The basidium enlarges and the twonuclei fuse (karyogamy). The zygotegoes through meiotic divisions, theresulting four haploid nuclei meanderinto the sterigmata forming thebasidiospore initials. It has beensuggested that the enlarging vacuole inthe basidium squeezes the cell contentsinto the basidiospores.

Basidiomycete Macrofungi

Reminder, these are the types ofFungi we are talking about.

Basidiospore release

Basidiospores developed at the tips ofsterigmata. Buller’s drop is somehow involvedin the basidiospore discharge. How, we do notknow. As a matter of fact we do not even knowwhether the droplet is membrane bound or justliquid adhering to the side of hilar appendix.The germinating basidiospores establishhaploid mycelium which we call primarymycelium.

Theory:Buller’s drop may be a CO2 bubble whichbreaks the cell walls at hilar appendix.Same electric charge of strerigma and thespore repels the spore on its merry way.


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Meisporic vs. mitosporic reproduction

Asexual reproduction may be of lesserimportance in basidiomycetes than it is inascomycetes (rusts and smuts are anexception to this rule).

Nonetheless, budding and mycelialfragmentation occur.

Some species may produce arthroconidia,which basically are hyphae fragmented intounicellular propagules.

Examples of arthroconidia production


Although vegetative fragmentation iscommon, mitospores are fairly infrequentamong the basidiomycetes

Haplophase or primarymycelium

Spore germination

Anastomosis of compatiblemycelia. Compatible matingtypes

Vegetative dikaryophaseor secondary myceliumdominant phase

Organized specializedtissues in the basidiocarp– tertiary mycelium

Basidiomycete Macrofungi - life cycles

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• Basidiomycetes do a great number of things.They do also have a great variety of means toget their spores “out there.”

The typical basidiomycete bearsits spores on the gills of a cap;Amanita sp.

Tremella - a jelly fungus - on aStereum - a conk or a polypore

Auricularia auricula anotherbasidiomycetous jelly fungus


• Basidiomycetes do a great number of things.They do also have a great variety of means toget their spores “out there.”

Geastrum - an earth star - is acommon puff ball - also amember of Gasteromycetes

Calvatia gigantea - an appropriatelynamed Gasteromycete

Nidulariales - the bird nest fungi - arealso members of Gasteromycetes

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They can form mutualistic symbioticassociations such as mycorrhizae, or live assaprobes on wood, soil, leaves, or dung.

Galerina autumnalis - asaprotrophic agaric

Russula amoenolens - abrittle mushroom - and itsmycorrhizae


There are also lichenized agarics,Omphallina umbellifera being agood example of this.

Lichenized fungi are mainlyascomycetous - apothecial,perithecial, ascostromatal. Takentogether this implies that the lichensymbiosis must be a very successfulsymbiosis.

Omphallina umbellifera - alichenized agaric


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Summary

• Agaricus commercial growing.

• Basidiospore production and release.

• Clamp connections and their meaning.

• Different types of basidiomycetes.

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