BIOSCI 108: Lecture 6 - The Magic of Mushrooms & Other Fungi

Eukaryotic Microbes

There are lot of eukaryotic microbes and they tend to be prominent members of ecosystems. However, some can be human pathogens. The two major groups of microbial eukaryotes are fungi and protists/protozoa

Common Features of Eukaryotes

• Eukaryotes all have nucleus
• Eukaryotes have membrane-bound organelles (mitochondria, chloroplasts, etc)
• Eukaryotes are more structually complex and larger than prokaryotes
• Some eukaryotes have cell walls (plants use cellulus, fungi use chitin, etc)

Differences Between Eukaryotes & Prokaryotes

• Eukaryotes have a nucleus
• Eukaryotes have membrane-bound organelles
• Eukaryotes don't have peptidoglycan cell walls
• Eukaryotes have lots of introns
• Eukaryotes have linear genes
• Eukaryotes can't grow above 100°C

Fungi

Eukaryotic cells that reproduce using spores, are chemoorganoheterophs, saprophytes, and are major decomposers in terrestrial (and some aquatic) ecosystems. They lack chlorophyll!

They're needed to degrade organic material and recycle it into something usable by others. But many are pathogenic to plants and animals.

They tend to also develop relationships and associations with other organisms (mycorrhizae and plant roots, lichen and algae).

It's six groups are:

• Chytridiomycota
• Zygomycota
• Glomeromycota
• Basidiomycota
• Ascomycota
• Microsporidia

Chemoorganoheterotrophs

Organisms that obtain nutrients and energy by breaking down organic compounds

Saprophytes

Organisms that absorb nutrients from dead organic material by releasing degradative enzymes to break them down. Fungi also use osmotrophy to absorb solube products.

Fungi Industrial & Research Applications

Industrially, we use it for fermentation in foods, to create organic acids, to produce certain drugs, to make some antibiotics (penicillin) as well as immunosuppressive agents.

Some fungi serve as yeast models that help us research more about genetics, cell biology, cancer, and so on.

Chytridiomycota

Also known as chytrids, are considered the simplest fungi. They're typically free living and saprophytic. They can also be pathogens for aquatic plants and animals.

They produce zoospores with flagellum that can participate in either sexual or asexual reproduction (most primitive form)

They're important decomposers of cellulose and keratin.

Batrachochytrium dendrobatidis (Bd)

A type of chytrid that has been responsible for amphibian declines globally. As their zoospores enter environments and settle on and colonise amphibian skin, it causes anoxeria, skin shedding, osmotic imbalance, and death.

However, some natural amphibian skin microbiota may be able to inhibit Bd from colonising.

Basidiomycota

Also known as basidiomycetes (club fungi) are the typical fungi we think of like toadstools, mushrooms, shelf fungi, puffballs, and so on. Many are edible but some are non-edible too.

They're important decomposers of detritus (wood and plant matter). But, certain rusts and smuts can also be pathogens to plants.

Myrtle Rust

A fungal disease caused by a basidiomycete that affect members of Myrtaceae (pohutukawa, feijoa, etc). It has first blown over across Tasman from Australia and first detected in NZ in 2017.

Ascomycota

Also known as ascomycetes (sac fungi) are typically found in freshwater, marine, and terrestrial habitats. They're also the red, brown, and blue-green moulds that causes food spoilage.

Some are also human and plant pathogens. Some are also edible as in the case of yeasts (Saccharomyces cerevisiae) and truffles

Claviceps purpurea & Stachybotrys

The former being a parasite that affects higher plants like ryegrass. This parasitism leads to ergotism that affects other organisms that consume infected grain.

The latter being black mould that's associated with damp buildings. They lead to respiratory illnesses such as asthma.

Metabolic Capabilities of Fungi (and example)

Fungi have various metabolic capabilities, being able to use a variety of molecules as energy and producing waste that humans can exploit.

The beneficial ones we use are typically seen in fungi that ferment products to make certain products (breads, wines, drugs, penicillin, etc).

The wine industry heavily depends on yeasts to drive the fermentation of grape juice into wine.

Yeasts would undergo anaerobic respiration of the sugars present in the grape juice (or whatever else). The sugar is split, converted into pyruvate, and then to ethanol (or other waste in other fungi).

Traditionally, the natural yeasts present in the grape juice would drive the fermentation. However, contemporarily, specific commercial wine strains are used.

Saccharomyce cerevisiae

Also known as baker's yeast, is the most common yeast used in the fermentation of foods.

Typically during a fermentation, it starts out as a rare wild ferment but quickly starts to dominant over time with the use of niche construction.

They would modify the environment by producing lots of ethanol and heat to kill off competitors. S. cerevisia are better adapted to the high pH (from alcohol), high temperatures, and osmotic stress (from all the molecules present).

Niche Construction

The process in which organisms, through their own behaviors, alter the environment and create circumstances that benefit them.