Fungi

Biology 342

Fungi Cells

Kingdom: Fungi

Fungi are eukaryotic single or multicellular organisms

Fungi membranes have chitin to add rigidity

Most fungi lack flagella thus immobile gametes

Microstructure consists of two forms: thread-like hyphae and branch-like Mycelium

Classification History of fungi Fungi were first described as plants in 1729 in a

publication “Nova plantarum genera”.

Fungi were considered a type of plant for nearly 250 years. 1729 – 1975 : fungi were placed in Kingdom

Plantae 1980 - 1990: structural and molecular work

began to raise questions… 1993 : Fungi firmly in its own Kingdom:

Fungi DNA sequencing demonstrates that fungi

are more closely related to animals than to plants.

Interesting facts

The oldest fossil fungi – a chytrid is from the late Precambrian (550 million yrs ago).

Fungi are primary decomposers of dead plant and animal tissue releasing back into the atmosphere billions of tons of carbon each year.

Fungi are immobile so disperse around the world with spores riding on air currents.

Fungi feed by the absorption of nutrients released by secreted digestive enzymes.

Fungi can reproduce asexually and sexually.

Fungi are genetically and chemically very similar to animals making fungal diseases difficult to treat.

Kingdom Fungi: Divisions

Chytridiomycota – Chytrids

Zygomycota – bread molds

Ascomycota – Yeasts and Sac fungi

Basidiomycota – Club fungi

Basidiomycota

Mushrooms, puffballs and shelf fungus

Many types are consumed as delicacies, others are poisonous

Cryptococcus is a human yeast pathogen found in bird droppings – when inhaled can cause meningitis and encephalitis

Zygomycota

Molds of bread and fruits

Mycorrhizal fungi – live on roots of vascular plants – take-up phosphate ions from soil – forms a network that connects individual plants together – sharing water and nutrients

Parasites of plants, insects and other small animals

Chytridiomycota

All are aquatic

Only fungi with flagellated gametes

Parasites of plants and insects, no direct impact on humans

Chytridiomycosis – emerging infectious disease of Amphibians spreading world wide contributing to their global decline

Ascomycota Yeasts, molds, and sac fungi

Cultivated by leaf-cutter ants

White-nose Syndrome – an emergent infectious disease in bats killing millions, bat declines in the NW US at 80%

Candida skin infections in humans

Valley fever, Coccidiodes immitis in people

Aspergillus on peanuts generates Aflatoxin which damages livers and is carcinogenic

Ergotism in people

Spreading Fungal Diseases

Coccidioidomycosis (valley fever) caused by Coccidiodes immitis.

Human Pathogenic Yeast (Fungal meningitis) caused by Cryptococcus spp.

Chytridiomycosis (Amphibian disease) caused by Batrachochytrium dendrobatidis.

White-nose Syndrome (bat disease) caused by Pseudogymnoascus destructans.

Ergotism

Rye Ergot fungus, Claviceps purpurea

Fungus grows on cereal plants, especially rye but also triticale, wheat and barley

Produces an alkaloid called ergotamine that when ingested by humans and other mammals causes the disease known as Ergotism

Symptoms include hallucinations, stomach cramps, burning sensations in limbs referred to as “Saint Anthony’s Fire”.

Salem Witch Trials In the winter of 1692-1693 in

Salem, Massachusetts 140 people were arrested and 20 women were hanged for witchcraft.

The “witches” where accused of hexing a dozen young girls that exhibited violent fits, convulsions, incoherent ranting, strange burning sensations on their skin and then going into trances.

Rye bread was a major part of the girls winter diet.

Emerging Infectious Disease Chytridiomycosis = Chytrid Amphibian enzootic

Fugal parasite of frogs and salamanders in the old world – first observed early1900’s.

African clawed frog is unaffected by infection.

Today the fungus has spread world wide- the Americas, Australia, Europe, Caribbean….

Today 30% of global amphibian populations are affected – with catastrophic declines of local populations - some disappearing from a location in a single year.

100% mortality in some populations with no way to control the chytrid fungus

Chytrid fungus

First case in NA – 1978

African Clawed frogs (Xenopus laevis) 1930 -1940 imported WW for pregnancy testing, laboratory research and for the pet trade – breeding programs shipped 20,000/yr. in 1970’s.

American Bullfrog (Rana catesbeiana) shipped worldwide for food in high-end restaurants.

Both these frog species escaped or were released and have become established everywhere– both are unaffected carriers of chytrid fungus.

Chytrid is widespread in California – N. leopard frog

White-Nose Syndrome

Fungal growth around the muzzles and wings of hibernating bats – first observed in US in 2006.

From one cave in New York it has spread to 25 states and five Canadian Provinces.

It kills > 90% of bats within 5 years of invading a hibernacula – there is no known treatment.

It is estimated to have killed from 6 to 7 million bats since its invasion of North America.

Bats consume tons of insects which is beneficial to agriculture and public health

Emerging Infectious DiseaseWhite-nose – bat enzootic

The fungus is cold-loving and will not grow above 68 degrees F.

In winter when bats are hibernating the fungus grows on their skin causing lesions and waking them during their torpor – expending fat reserves and they die before summer.