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Biology of FUNgi

Lecture 4The non-fungi

A look back...

• What is a biotroph/saprotroph?

• What is an obligate/facultative biotroph?

• What is the 3 domain system?

• Where do fungi fit in this scheme?

• Where are the non-fungi?

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“Fungus” of the day - Dictyosteliumdiscoides

Taxonomy: Phylum (subphylum) Dictyosteliomycota Order - Dictyosteliales Family - Dictyosteliaceae Common names: “the slug”

What is it: Cellular slime mold. D. discoides has anamoeba phase which is phagotrophic on bacteria. Anoutstanding example of healthy family dynamics: thezygote forms a macrocyst, which digests other “loving”members of the family.D. discoides is among those haploid organisms whichhave been chosen as model organisms for cell cycle andgenome research.

Life cycle is a kick as well.

D. discoides amoebaand a sorocarp

“Fungus” of the day - Dictyosteliumdiscoides

Life cycle

From Alexopoulos et al. 1996

Plasmogamy = cytoplasmsfuse; dikaryote phase

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The giant zygote =macrocyst

Primary cell walls surrounddikaryotic macrocyst andsurrounding fellow amoeba

Zygote feedson the fellow amoebacannibal

Karyogamy = nuclei of thedikaryote fuse; diploid phase

Meiotic division of themacrocyst; return tohaploid phase

Check out p. 15-20in Carlile

Sorocarp = sorus-containingstructureThe SlugSorus = mass of spores orsporangia

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“Fungus” of the day - Dictyosteliumdiscoides

Life cycle

Fruiting body =sorocarp

Pseudoplasmodium= slug

From http://dictybase.org/

“Fungus” of the day - Dictyosteliumdiscoides

For tid-bits and more trivia check following;

D. discoides as a model for biomedical research:http://www.nih.gov/science/models/d_discoideum/

Movies – aggregation stream and more:http://www-biology.ucsd.edu/~firtel/movies.html

D. discoides genome project:http://genome.imb-jena.de/dictyostelium/

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A look ahead...

• Let’s dive into the protistan tail from thedeep end. In other words, let’s look at thenon-fungi.

• True and cellular slime molds.

• Biflagellates - the oomycetes

Kingdom Fungi in three domains

The true fungi would include fourfungal phyla.

The rest of the organismspreviously considered as fungiwould mainly be protistan. Let’slook at those.

This is also known as the approachof climbing to a tree from the base.

Chytridiomycota

Basidiomycota

Ascomycota

Zygomycota

Animalia

?

?

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The non-fungi

These are the groups studied bymycologists, but not included in the modernkingdom Fungi.

Currently, they seem to fall into phyla oftheir own - e.g. Dictyostelium, a cellularslime mold, Physarum - a true slime mold,Achyla - an oomycete.

AnimaliaFungiPlantaeProtistaMonera

From Pace 1997 Science 276: 734-740.

The non-fungi - what are they?

What are fungi?

Heterotrophic, mainly aerobic andfilamentous eukaryotes whichobtained nutrients and energy byabsorbing compounds from theirsubstrate. They were characterizedby septate or aseptate hyphae madeof chitin.

From Alexopoulos et al. 1996

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The non-fungi - what are they?

What are the non-fungi?Three groups of organismshistorically included in fungi.

1) The true fungi - Kingdom Fungi

2) Stramenopiles - fungus-likeorganisms with flagella.

3) The slime molds - protistanamoeboid groups.

From Alexopoulos et al. 1996

The non-fungi - what are they?1) The true fungi - Monophyletic,well-supported

2) Stramenopiles - Monophyletic,somewhat well-supported

3) The slime molds - evidentlypolyphyletic

From Alexopoulos et al. 1996

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The slime moldsFirst group are the so-called slimemoulds (protozoan). Not fungi becausethey are

1) Phagotrophic (amoeboid), notabsorptive

2) Not hyphal, ever

3) Assimilative plasmodia usually haveno cell wall (exception cellular slimemoulds).

Note that these are clearly notmonophyletic and a uniform group.

Physarum - trueslime moldDictyostelium -

Dictyoistelidcellular slimemold

The slime mouldsWe will consider two of the four phyla.

1) Phylum Dictyostelimycota(Dictyostelida) - cellular slimemoulds

2) Phylum Myxomycota(Myxostelida) - true slime moulds

3) Phylum Acrasiomycota (Dictyostelida) -cellular slime moulds4) Plasmodiophoromycota (Plasmodiophorida) -endoparasitic slime moulds

Note: there is a serious incongruencehow your text treats these phyla

From Alexopoulos et al. 1996

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Phylum Dictyosteliomycota –cellular slime moulds

The “fungus” of the day was an excellentexample of the cellular slime molds.Characterized by1) Phagotrophic haploid amoeba2) Pseudoplasmodium - multicellularsomatic phase3) reproductive stationary sorocarp

From Alexopoulos et al. 1996

Phagotrophic myxoamoeba

Myxoamoeba aggregate toform pseudoplasmodium Pseudoplasmodium which will form

the sorocarp - Dictyostelium

Phylum Dictyosteliomycota –cellular slime moulds

Main difference betweenDictyosteliomycota and Myxomycota isthe presence or absence of individual cellsin the (pseudo-)plasmodium.

Habitat and occurrence

Common in soil, dung and decaying plantmaterial.Remain unseen because sorocarps areminuscule.Phagotrophically feed on bacteria on thesubstrate

Sorocarp - Dictyosteliumdiscoideum

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Phylum Myxomycota –true slime moulds

Carlile p. 20-25.

Characterized by1) Phagotrophy2) Three types of uninucleate, haploid cells: spores,swarm cells, myxoamoeba3) Multinucleate somatic phase; true plasmodium4) reproductive stationary sporangium

From Alexopoulos et al. 1996

Plasmodium - motile,chemostatic, not cellular

Stemonitis fuscasporangia

Phagotrophic myxoamoeba

Swarm cellsHaploidMyxoamoeba

Haploid spores

KaryogamyZygotePlasmodium

Resting stage, sclerotium

Sporangium

Meiosis

Phylum Myxomycota –true slime moulds

OccurrenceCosmopolitan group, in moist temperateforests, lawns, flower beds.Usually, on wood, leaves or bark.Substratum, however, is more of a habitat -myxomycetes feed on bacteria and organicparticles (phagotrophs).

Physarum cinereum on tallfescue leaves in Kansas

Fuligo septica - troll butter - isanother common myxomycete onlawns; stalkless sporangiaStemonitis fusca - young and mature

stalked sporangia

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Phylum Myxomycota –true slime moulds

Myxomycete trivia- Fuligo septica is fondly called the blob- 1973 was exceptionally wet year; F.septica seemed to enjoy these favorableconditions

A quote of a sheriff’s report:…, an unidentified Growing Object (big asplatter, foamy and creamy and pale yellow)terrorized Mrs Harris’s backyard for threeweeks. Apparently, the blob died of asunstroke and nicotine poisoning - rainsceased and Mrs. Harris was a heavysmoker.

Fuligo septica - sporangia

TheBlob - a horror moviefrom 1958

More non-fungi...Second group includes the Oomycotain stramenopiles a.k.a. biflagellates

An odd number of other fungus-likeorganisms (e.g. hyphochytrids) and algaealso belong to this group

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Oomycetes - the water molds

Stramenopiles were those organismsthat are united by presence of twoflagella (biflagellates) of unequallength, form or movement(heterokonts). Monophyly seems tobe somewhat well supported.

Oomycota (water moulds)- these are more similar to eufungi -absorptive nutrition

Oomycetes are oomycetes because…

1) Asexually reproduce with zoospores (heterokont,biflagellate) with a hairy tinsel flagellum and asmooth whiplash flagellum

2) After fertilization, diploid thallus which formsgametangia

3) Sexually reproduce by gametes; plasmogamyand karyogamy result in resting structure known asoospores.

4) Cell wall usually not chitinous; glucans,cellulose. Some species may have chitin.

Saprolegnia sp. -oospores.

A zoospore with tinsel (onewith hairs on the flagellarmembrane) and whiplashflagellum (One without thehair)

Saprolegnia sp. -zoosporangia.

Oomycetes - the watermoulds

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Significance and occurrence...

The zoospores need water for dispersal -hence the flagellum.

Most of the aquatic oomycetes are saprobesdecomposing the remains of dead plants andanimals - a major component in nutrientcycling in rivers and lakes.

Many aquatic species are parasites of fishand their eggs.

The woolly patches on thehatchery fishes are oftenSaprolegnia.

Oomycetes - the water molds

Also terrestrial species. E.g. Phytophthorainfestans, the causal agent of potato blight.P. infestans is also the cause of the greatIrish famine, which resulted in the greatIrish migration to North America.

Phytophthora infestans. -zoosporangia.

A zoospore with tinsel andwhiplash flagellum

Foliar necrosis resultingfrom potato blight

Taters infected withPhytophthora infestans (soft rot)

Oomycetes - the water molds

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Significance and occurrence...

Although many oomycetes are aquatic andsaprotrophic, there is at least one example ofterrestrial disease-causing oomycete Pythiuminsidiosum.

Pythium insidiosum causespythiosis in mammals.

P. insidiosum can alsoinfect humans.

Oomycetes - the water molds

Phylum Oomycota –oomycetes

Life cycle.

Key points to ponder:

- diploid, mitotic zoospores, which mayform resting cysts. Some species likeSaprolegnia go through encystmentmore than once.

- Meiosis occurs in oogonium andantheridium

- plasmogamy and karyogamy give riseto a zygote, oospore

Mitotic zoospores Mitotic zoospores

Thallus withsporangia

Gametangia

Gametes

Plasmogamy

Karyogamy

Resting cysts Resting cysts

Thallus withsporangia

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Phylum Oomycota –oomycetes

Oogonium andantheridium

Oospore

To sum up...

• Eufungi vs. slimemolds and biflagellateOomycetes

• Lifecycles of slimemolds and Oomycetes

• The significance and occurrence of the non-fungi