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Biology of FUNgi

Lecture 07Deuteromycetes - the mitosporic

fungi

A look back...

• What are Archiascomycetes?

• What are Saccharomycetales?

• What separated the primitive ascomycetes from thefilamentous ascomycetes?

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Fungus of the day -Penicillium chrysogenum

Taxonomy: Phylum (subphylum) Ascomycota Order - Eurotiales (anamorphic) Family - Trichocomaceae

Today we will share one of the greatest successstories of a sloppy microbiologist. We will beintroduced to the discovery and production ofpenicillin by Penicillium chrysogenum. It is a fungus on a dish.

Penicillium chrysogenum

A typical conidial synnemaof Penicillium

Fungus of the day -Penicillium chrysogenum

This is also a wonderful story in history ofmicrobiology or mycology. Sir Fleming returnedfrom a vacation to his Staphylocuccus cultures in1928. The cultures were contaminated withPenicillium notatum. He isolated the culprit whichkept his bacteria from growing.

Using this culture, group of scientists were able toestablish first culturing facility to produce enoughpenicillin to start experimental tests on theantibiotics.

Sir Alexander Fleming

Fleming’s contaminatedplate.

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Fungus of the day -Penicillium chrysogenum

After numerous trials on different types ofculturing devices, this group in Oxford found thatbest culturing conditions could be establishedwith hospital bedpans renamed promptly“penicillium flasks”.

First trials of penicillin were a grand success.Albert Alexander’s condition was greatlyimproved after ca 1g of penicillin. Penicillin wasnot abundant enough to save his life, it needed tobe repurified from his urine to be able to continuetreatment. He eventually died as a result of hisinfection.

Bedpan cultures for penicillinproduction

Fungus of the day -Penicillium chrysogenum

The British may not have had enough experience inlarge-scale production of fungal metabolites.Americans were far ahead in this game; they wereusing fermentors to produce citric and humic acidsalready. Citric acid is used in soda, it may be thatsoda came to rescue the world from infectiousdiseases in this respect.

In addition to providing the system for culturingfungi for penicillin, Mary Hunt from Peoria IL,found the hyper-producer strain of Penicilliumchrysogenum which replaced the original P. notatumstrain. She bought the moldy cantaloupe at a localmarket.

Fermentors used forpenicillin production

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Fungus of the day -Penicillium chrysogenum

To exemplify the importance of penicillin, it mayhave expedited the end of WWII in Europe like thenuke did in the Pacific. Death from infectionsaccounted for 15% of total loss of troops in WWI,these were nearly absent towards the end of WWII.Needless to say, penicillin was not made available toaxis nations.

The point being, penicillin was the first effectivebiotechnologically produced antibiotic. Prior to thatwe were confined to sulfur and copper containingchemical drugs. Aren’t fungi wonderful!

Fermentors used forpenicillin production

A look forward…

• Saccharomycetales…

• What are the mitosporic fungi?

• How do the mitosporic fungi relate tomeiosporic fungi?

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• Saccharomyces cerevisaepointers for the life cycle

• Asexual reproduction bybudding in both haplo- anddiplophase.

• Heterothallism exists even intrue yeasts.

• The zygote develops into anascus after several diploidgenerations.

Phylum Ascomycota -Saccharomycetales

Generalized ascomycetelife cycle -focus onmitosporic phases

• Filamentous ascomycetes -ascogenous hyphae, ascocarp,forcible spore discharge andmodified ascus tip to allow thatdischarge.

• Also, (usually) no yeast-like phasein their lives.

• Many have a quicker means fordispersal - the mitoticconidiospores.

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The deuteromycetes - imperfectfungi

• Traditionally, the conidiospore and/or the conidiophorestructures as well as their development (conidiogenesis)

• This was called the Saccardoan system (after Saccardo1899).

• Saccardoan system may not reflect true evolutionaryrelationships - it is an artificial classification.

• Similar conidial structures may occur in different generaand families of meiotic taxa.

Deuteromycetes - the manyshapes of conidiospores

• Helicospores - trap a bubble of airto make them float in water.

• Staurospores - also an adaptation toaquatic environment; pegs coveredwith adhesive which will allowattachment to woody or leafsubstrate in streams (the Ingoldianfungi).

• Dictyo- and phragmospores - thick-walled and melanized, typical forsoil-inhabiting fungi; possibly anadaptation to avoid predation,desiccation or exposure to UV-radiation.

Staurospores andhelicospores

Phragmosporesand dictyospores

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• Coelomycetes - mitotic fungi whichproduce conidiospores in protectivestructures

• Hyphomycetes. Mitotic fungi whoseconidiophores are exposed.

Conidiophores of coelomycetesand hyphomycetes

An acervulus and a synnema -different types of conidiomata

Deuteromycetes - the manyshapes of conidiophores

Sexual vs. asexual stage

Mycelium - vegetative stage

Mitotic divisions andconidiophore differentiation –mitospores

Anastomosis, plasmogamy,karyogamy and meioticdivisions – meiospores

Same organism –dispersal by meioticvs. mitotic spores.

Aspergillus sp.

Eurotium sp.

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Same organism – two names?

Mycelium - vegetative stage

Mitotic divisions andconidiophore differentiation –mitospores

Anastomosis, plasmogamy,karyogamy and meioticdivisions – meiospores

Same organism – dispersal bymeiotic vs. mitotic spores.

Aspergillus sp.

Eurotium sp.

Same organism – two names?

Same organism – dispersal bymeiotic vs. mitotic spores.

Aspergillus sp. Eurotium sp.

Anamorphic - asexual stage Teleomorphic - sexual stage

Aspergillus Penicillium Eurotium Talaromyces

Eurotium Talaromyces

Holomorph

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Same organism – two names?

Aspergillus sp.

Eurotium sp.

Summary:

Anamorphic - asexual stage

Teleomorphic - sexual stage

If both known, we talk about a holomorph:e.g. Eurotium sp. with Aspergillus sp.anamorph

Eurotium Talaromyces

Holomorph

Deuteromycetes – different names forthe mitotic and meiotic stages

• Isn’t it confusing to have twonames for different organisms?

• Incentives– Many organisms have no known

sexual (meiosporic) stage

– Many mitosporic stages are verycharacteristic but may be hard torelate to the meiosporic ones

– Easy ID in pure culture.

• Initially the plan was to transfermitosporic taxa to meiosporicones after this was discovered. Aspergillus sp. culture and

conidiophore can be defined by theirmorphological characteristics - so canEurotium sp.

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The deuteromycetes - imperfectfungi

• How does one become imperfect?– Single mutation in a long line of expressed genes which result in the

production of a fruiting body?

– Hybridization (a debated issue in fungi - evidence is accumulating)may lead to loss. Too many tangling pairs of chromosomes interferewith meiotic divisions?

– Loss of mating types in heterothallic fungi. If one mating type is inmore of an advantage in certain regions or substrates, other matingtypes may become increasingly rare - or totally disappear from thepopulation. In other words, if we live under conditions that arecharacterized by a strong directional selection. An example:Ophiostoma novo-ulmi the causal agent of DED.

The deuteromycetes - imperfectfungi

• Among the European isolates of Ophiostoma novo-ulmi one mating type is very rare. This is assumedto be a result of strong directional selection in anew environment and new host taxa. The veryreason for predominantly asexual reproduction?

• In the case of another, but similar, disease causingagent Ophiostoma ulmi both mating types arepresent at equal frequences - no directionalselection?

Elm trees (Ulmus sp.)knocked out by Ophiostomanovo-ulmi

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Pros and cons of mitotic stages

• Muller’s Ratchet.

• Are mitotic species static? No! Mutation happens.Unfortunately, most mutations are deleterious.

• Does mitotic stage exclude sex? No! We just may not beaware of it; sexual reproductive structures are infrequentand/or minuscule - escape the mycologists’ sharp eyes.

• Recombination in absence of sex? Parasexual recombination.What is that?

The deuteromycetes - parasexualcycle

• Parasexual cycle refers to a situation where recombinationtakes place without sexual reproduction. How does thishappen?

• Four important requirements:– Heterokaryosis: two types of nuclei in a single mycelium -

anastomosis and insertion of a foreign nucleus (mother nature is abitch), mutations or chromosomal rearrangements.

– Karyogamy within somatic mycelium to establish stable orunstable diploid.

– Crossing over at mitosis in the diploid nucleus.

– Haploidization - recall no meiotic division

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The deuteromycetes - parasexualcycle

• The haploidization is likely to be acquired by aneuploidy,the gradual loss of chromosomes, until the normal haploidcomplement is restored.

• This sounds like science fiction. However, the recovery ofnon-parental types in somatic cultures evidencesrecombination events (zonation, changes in colony color,antibiotic resistance, nutritional requirements, conidialcharacters).

The deuteromycetes - occurrence

• Where do asexual ascomycetes the deuteromycetes occur?

• They inhabit same substrates and same habitats as theirsexual states do. Occasionally both may occur together.

• Like the ascomycetous teleomorphs, anamorphic or mitoticascomycetes occur in terrestrial, aquatic and marineenvironments.

• Some imperfect fungi are also parasites and diseasecausing agents of animals and humans...

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The deuteromycetes - imperfectfungi

• Aspergillus sp., for example, can infecthuman tissues causing mycoses orpulmonary discomfort withpneumonia-like symptoms

Typical Aspergillusconidiophores

Summary...

• Asexual dispersal by mitospores

• Holomorph = meiosporic + mitosporic state

• Causes and pros/cons of mitotic states

• Parasexuality