Chap 1 classification of fungi

MIC 206MYCOLOGY

CLASSIFICATION OF FUNGI

Sub-TopicBrief Criteria of the Fungi KingdomDifferences between the Old and Modern ClassificationDifficulties of Classifying FungiIntroduction, Basic Characteristics and Life Cycles

Definitions

MYCOLOGISTS MYCOLOGY MYCOSESFUNGUSFUNGI

Definitions

Mycologists : scientists who study fungi.Mycology : scientific discipline dealing with fungi. Mycoses : diseases caused in animals by fungi.

Fungus versus Fungi

“Fungus” is used inclusively for a heterogenous group of organisms that have traditionally been studied by mycologists .“Fungi” refers to the organisms in the Kingdom Fungi, the true fungi, also called the “Eumycota”.

How many species of fungi exist?

- 90,000 species of fungi described

- 1,700 new species described each year

What is a fungus? A eukaryotic organisms. Fungi are neither a plants, nor animals A heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption.Heterotrophic by absorption.Reproduced by spores. The primary carbohydrate storage product of fungi is glycogen.

Most fungi have a thallus composed of hyphae (sing. hypha) that elongate by tip growth. The fungal thallus consists of hyphae; a mass of hyphae is a mycelium.

Structure – hyphae, mycelium, thalusHeterotrophic by AdsorptionReproduced by Spores

The Characteristics of Fungi

Kingdom Fungi

Nutritional Type Heterotroph

Multicellularity All, except yeasts

Cellular ArrangementUnicellular, filamentous, fleshy

Food Acquisition Method

Absorptive

Characteristic Features

Sexual and asexual spores

Embryo Formation None

Structure of fungi

1) The Structure - HyphaeHyphae = tubular units of constructionTubularHard wall of chitinCross walls may form

compartments (± cells)MultinucleateGrow at tips

Modifications of hyphae

Hyphal growth

Hyphae grow from their tipsMycelium = extensive, feeding web of hyphaeMycelia are the ecologically active bodies of fungi

This wall is rigid Only the tip wall is plastic and stretches

Hyphal growth from spore

germinatingspore

mycelium

2. Heterotrophic by Absorption

Fungi get carbon from organic sourcesHyphal tips release enzymesEnzymatic breakdown of substrateProducts diffuse back into hyphae

Product diffuses backinto hypha and is used

Nucleus hangs backand “directs”

3. Reproduced by spores

Spores are reproductive cellsSexualAsexual

Formed:Directly on hyphaeInside sporangiaFruiting bodies

Amanita fruiting body

Pilobolus sporangia

Penicillium hyphae

OLD AND MODERN

CLASSIFICATION OF FUNGI

Carl Linnaeus (1707-1778) the “Father of Taxonomy”

“ Minerals exist; plants exist and live; animals exist, live and sense.” Plants without obvious sexual organs were classified in Class Cryptogamia (lichens, fungi, mosses, ferns)

Fungi are primitive plants under this classification of organisms.

Old Classification

The Five kingdom system (Whittaker, 1969)Eukarya (includes all organism with a nucleus & membrane bound organelles). Plants and Animals are fairly obviousFungi, are very distinct from the other kingdoms.Kingdom Protista is a “dumping ground” for organisms that don’t fit into the other eukaryotic kingdoms.

Old Classification

R. H. Whittaker’s 1969 Classification

KINGDOM

CHARACTERISTIC EXAMPLE

Monera Prokaryocyte BacteriaActinomyces

Protista Eukaryocyte Protozoa

Fungi Eukaryocyte * Fungi

Plants Eukaryocyte PlantsMoss

Animals Eukaryocyte * ArthropodsMammals

Man

Modern Classification At least 7 kingdoms are now recognized (Patterson & Sogin 1992) : Eubacteria, Archaebacteria, Animalia, Plantae, Eumycota, Stramenopila (Chromista), Protoctista (Protozoa, Protista)

Based on molecular evidence: base sequences from ribosomal RNA (Patterson & Sogin 1992)

Systems of classifying fungi 1) 1860

HOGG proposed the term PROTOCTISTA - fungi and neither Plant or Animal. This kingdom composed mostly of unicellular organisms. The kingdom was later replaced by 2 kingdoms – MYCOTA & MONERA (prokaryotes) and PROTOCTISTA(eukaryotes).

2) 1947Microscopes enable study of complex structural

characteristics.New classification (WOLF & WOLF, 1947)

3) 1969Fungi in its own kingdom by WHITTAKER – FUNGI KINGDOM.

Systems of classifying fungi

4) 1998Modification by MARGUILIS & SCHWARTZ – used characteristics (structure & function).

• MONERA: Prokaryotes – bacteria, actinomycetes, blue-green algae.

• PROTOCTISTA: Eukaryotes – protozoa and other unicellular and colonial organisms such as water moulds, slime moulds and slime nets.

• FUNGI : Eukaryotes – organisms that lack flagella that develop from spores such as yeast, molds, rusts and mushrooms.

• PLANTAE: Eukaryotes – organisms that develop from embryos such as liverworts, mosses and vascular plants.

• ANIMALIA: Eukaryotes – organisms that develop from a blastula (hollow ball of cells) such a sponges, worms, arthropods and mammals.

Marguilis and Schwartz (1998)

Classify the fungi into 3 phyla : Zygomycota, Ascomycota and Basidiomycota.

Chytrids (CHYTRIDIOMYCOTA) in the Kingdom Proctista.

Deuteromycota with their closest relatives that are the Ascomycota and Basidiomycota.

Lichen with the Phylum Ascomycota.

Other classifications MOORE, 1998 (quoted from Pfieffer, M., et al.,

2001) states that plants, animals and fungi can be separated based on how they obtain energy.

Plants possess chloroplasts as photosynthetic structures used to produce food.

Animals possess mitochondria used for internalized digestion.

Fungi excrete enzymes into the food source they live within external digestion.

Classification using molecular research techniques

BALDAUF & PALMER (1993), WAINWRIGHT et al. (1993) and HASEGAWA et al (1993)

The above current schemes agree that the three major kingdoms are separated

→ thereby confirmed that there are no connection between the fungi-plant kingdom.

Question

Fill in the blanks of the systematic of classification

1) Kingdom2) Division / Phylum3) ___________ 4) Order5) ___________ 6) Tribe7) ___________ 8) Species

Sometimes there are subdivisions and subclasses

Question

Fill in the blanks of the systematic of classification

1) Kingdom2) Division / Phylum3) Class 4) Order5) Family 6) Tribe7) Genus 8) Species

Sometimes there are subdivisions and subclasses

Hierarchical Classification

Kingdom Fungi Phylum Basidiomycota Class Basidiomycetes Order Agaricales Family Agaricaceae Genus Agaricus Species: Agaricus campestris L.

How are fungi named?

To determine the correct name for a taxon, certain steps must be followed, including: Effective publication Valid publication

• Description or diagnosis in Latin• Clear indication of rank• Designated type

NomenclatureNomenclature: the “allocation of scientific names to the units a systematist considers to merit formal recognition.” (Hawksworth et al., 1995. The Dictionary of the Fungi). 

The nomenclature of fungi is governed by the International Code for Botanical Nomenclature, as adopted by the International Botanical Congress.

Reasons why it is not easy to classify fungi

Fungi comprise of a broad number of organisms.Fungi have various forms depending on the environment and conditions in which they grow.Many terms being used to describe the morphological structures of fungi.

Basic Characteristics and Life Cycles

Ascomycota (inc.Deuteromycota)BasidiomycotaZygomycota

Ascomycota – “sac fungi”

Teleomorphic fungi Produce sexual and

asexual sporesSex. – asciAsex. – commonCup fungi, morels, trufflesImportant plant parasites & saprobesYeast - SaccharomycesSeptateMost lichens

A cluster of asci with spores inside

Basidiomycota – “club fungi”

Produce basidiospores and sometimes conidiosporesSex – basidiaAsex – not so commonLong-lived dikaryotic myceliaRusts & smuts – primitive plant parasitesSeptateMushrooms, polypores, puffballsEnzymes decompose woodMycorrhizas

SEM of basidia and spores

Zygomycota – “zygote fungi”

Conjugation fungiCoenocyticSex - zygosporangiaAsex - common

Produce sporangiospores and zygosporesHyphae have no cross wallsGrow rapidlyRhizopus, Mucor (opportunistic, systemic mycoses)Mycorrhizas

Fig 31.6 Rhizopus on strawberries

True Fungi versus Slime MouldsTrue fungi:- those that are hyphal- possess cell walls throughout most of their life cycle - are exclusively absorptive in their nutrition.

Slime moulds:- those that do not form hyphae- lack cell walls during the phase that they obtain nutrients and grow- are capable of ingesting nutrients by phagocytosis.

So they are more common to Protista although they produce fruiting bodies like fungi.

- The most studied of them are the cellular slime moulds and the plasmodial slime moulds or Myxomycetes.

QUESTION

The fungus can never be classified in

Plantae or Animalia?

EXPLAIN WHY?

(Hint ! LOOK AT ITS MOBILITY, REPRODUCTION & NUTRITION)