Lecture 6- Fungi

Hyphae

1. Septated- can see compartments with just one nucleus inside each cell 2. Not septated- several nuclei floating around in the cytoplasm and the cytoplasm will be common to a group of nuclei Most fungi have cell wall like bacteria does. You even see the same component- NAG * Unlike bacteria, it's not an alternation to NAC and NAM and there's no peptide cross-linking. it's just a polymer of NAG-- chitin Chitin is also found in anthropods who's shells are made of that. Presence of cell wall is another main distinction between fungi and animal. Animals do NOT have cell walls.

Mycoces

1. Superficial- surface area: hair, skin, nails 2. Subcutaneous- deeper layers of skin 3. Systemic- fungal growth in internal organs of the body Examples (opportunistic): Candida abicans- yeast infection Cryptoccocus nectonans- one that the human body is usually able to fight and even tolerate sometimes found as part of our flora. but when our immune system is weakened, the pathogen can grow in higher numbers and become a source of problems It was often found in association with HIV Aspergilus fumigatus

Rhizopus (Black Bread Mold) Sexual Life Cycle

2 mating types (+) and (-) 2 organisms- make phermones, certain branches of the hyphae are going to move in the direction of the other and they will fuse and then you have plasmogamy- fusion of cytoplasm and at this stage, the formation of the zygosporangium already starts but you stil have a heterokaryotic situation because the nuclei are floating in the cytoplasmbut they're not fused. Then you have the fusion and the completion of the formation of the zytosporangiu ad eventually meiosis to go back from the diploid to the haploid. Then, you get dispersal of the spore. **The very important difference between these 2 cycles is that during the diploid stage and before and after meisosis, the chromosomes coming from the 2 parents can recombine and you get genetically diverse spores

Lichen

Accounts for 1/5 of all known fungi Shape and structure of the lichen depends on the fungal component The algal cell is completely surrounded by fungi. alga receives protection from fungus and fungus gets carbon. So, fungus can grow on rocks. Doesn't need to get food from the thing its attached to like the rock. So lichens are photosynthetic but it's not the fungus part that's photosynthetic but the alga or the cyanobacteria that the fungus associates with. You have large structure due to the fungus and then you have 1 layer of photosynthetic organism.

Phylogeny of Fungi

Ascomycetes- 2/3 of all fungi Basidiomycetes- 2nd largest

Saccharomyces cerevisiae*(Baker's/Budding yeast)

Bud will grow until it separates from the mother cell. On the mother cell you will see a budding scar which indicates that there was a process of division. You can define the age of a yeast cell by identifying the number of buding scars (number of times it divided) For eukaryotic organism, it has a very short generation time, divides every couple of hours. Great for experiments!

Penicillium

Deuteromycetes Imperfect fungi used for 1st time in 1942 discovered by accident by Alexander Fleming when he left his plate stand and it got contaminated by a colony and around the colony there was a zone where the growth of bacteria was inhibited. so this organism makes a compound that kills bacteria

Lifestyles

Different ways to get nutrients: 1. Decomposers (saprobes)- dead organisms or waste from living organisms 2. Parasites 3. Mutualistic Symbionts

Penicillium Structure

Discovered by Dorothy Hodgkin The beta-lactam is the main thing that makes it special.

Fungal Pathogens

Disease: 1. Toxin production- mycotoxins ex. Ergotamine- grew on rye- flour---> hallucinations 2. Infections- mycoses (somtimes on skin but sometimes inside tissue) 3. Allergic responses

Chytrids

Diverged the earliest in the fungal evolution *Their spores are flagellated Flagella helps in the process of dispersal of the spore. This implies you need energy to have the flagella moving, which means they're not fully dormant. So there's a bit of metabollic activity. Other than that, they're a typica fungi as they form hyphae and have spores and fruiting bodies. Not all of them have cell walls (kind of like bacteria which also not all have cell walls eg. mycoplasma) The cell wall is made of chitin

Aspergillus

Doesn't have sex either and also formes spores that are slightly different shape. Here the conidiophore is globe like rather than branch like.

Feeding

Fungi are heterotrophs that feed by absorption. They do not ingest their food nor are they phototrophic. They digest food outside of the body as the large molecules are broken down into smaller compounds that can be absorbed. Broken down by hydrolytic enzyme- exoenzyme Fungi grow next to their main source of nutrients- most fungi are not motile, except some flagellated fungi Symbiotic relationship: ants and leaves and fungus degrade the leaves

Fungi

Fungi are the closest organisms to animals. They are sister kingdoms. ~ 1 billion years old Fungi has both multicellular and unicellular organisms. Choanoflagellates (protist)- unicellular Animals-multicellular Fungi is important ecologically as it is responsible for breaking down organic material and recycling nutrients. They also produce antibiotics like penicillin, but they can also cause disease Most lack flagella but evolved from flagellated ancestor (chytrids)

Plasmogamy

Fusion of cytoplasms

Syngamy

Fusion of gametes

Karyogamy

Fusion of nuclei

Multicellular Body Structure

Grow in filaments and make large networks of filaments because since they grow next to sources of food, they want to maximize their interaction with the food ex. decaying trunk of tree, fungus will cover the whole trunk and it's not just macroscopic but also microscopic. There are networks of philaments - hyphae ** Network= mycelium Also grow upwards which is called arial hyphae and at the tip you have spore producing structures. Spore will be the vehicle that the fungus will use for dispersal These spores are different from endospores and the spore you find in dictostereum but the concept is the same in the sense that it's a dormant form of the organism that can be dispersed. In this case, water or wind or animal can disperse it. Once its in a favorable environment, spores will germinate and no longer dormant.

S. cerevisiae Life cycle

It's a true ascomycede because you find the spores after the meisoiss in the structure called ascus. You can isolate individual spores if you dissect the ascus and take the four spores. So you can innoculate a culture with just a single spore. Prefers to reproduce sexually Can be found as a diploid or haploid

Lysergic Acid Diethylamide

LSD is synthetic. Developed in a lab because there was a possibility it could be a therapeutic drug. Albert Hofmann.

S. cerevisiae as a genetic tool

Lethal mutations can be studied in haploids and maintained in diploids Foreign DNA can be introduced into yeast cells by electroporation and integrated by homologous recombination. Yeast artificial chromosomes - YACs Eukaryotic proteins can be expressed with correct post-transcriptional modifications You can do crosses if you have a lethal mutation. you can maintain it in a dipolid because then one gene will be wild type and the other will be mutated. If you want to study the effect of the mutation, you can go through making spores and haploid and study the lethal mutation in the haploid. you can bring foreign DNA inside and you can integrate it. you can put an artificial chromosome as piece of extra genomic material inside cell. advantage if yeast over bacteria is that it's a eukaryote with a golgi and do some post translational modification like glycocylation that only eukaryotic cells can do. Used it to help identify cyclins that are regulators of the cell cycle.

Zygomycetes

Make zygosporangia known primarily for food spoilage. They form colorful fruiting bodies called zygosporangia. Found as instances of food spottage like black bread mold (Rhizopus) This is an example of low class of fungus because the hyphae is not septated- coenocytic*

Encephalitozoon cuniculi- microsporidian- zygomycete

Parasite- no mitochondria Lost most of its morphological characteristics as a result of its parasitic life style Organism that was curious and unclear that it was a zygomycete until recently. Microsporidian is important because for a long time it was thought of as a primitive eukaryote. That was primarily because it didn't have a mitochondria. But really it's because it's a eukaryote that went through a process of evolution where it lost its mitochondria. Although its small genome really matches the genome sigature of zygomycetes and since fungi evolved relative late in the tree of life , the theory that it was a primitive eukaryote can be discarded. It lost so many of its genes and mitochondria and characteristics because it's a parasite and parasites don't really need all that stuff as it can rely on the host for most of its nutrients and most of what it has to do, so it doesn't even need a mitochonria. it kept some characteristics- life cycle- it can sporulate

Transglycosylation and Transpeptidation

Penicillium inhibits the function of the transpeptidase which makes the cross links between peptides in the bacterial peptidoglycan.

Asexual and Sexual Life Cycle

SEXUAL cycle starts with mycelium with nuclei that are haploid. There will be fusion of the two opposing maturing types and they will combine their DNA to make a diploid organism. That suggests that there's a fusion of the gametes- syngamy* In animals you don't distinguish the different stages in this process because it happens so fast but in fungis you can because first there's fusion of cytoplasm where you have the 2n stage with genome contact of the 2 mating types together in the same cytoplasm but they have not yet fused- karyotic stage Then you have fusion of the nuclei-karyogamy Then you have the diploid. Important thing with fungi is that this stage between plasmomy and karyogamy can be pretty long- few days sometimes Spores are always haploid and go through meiosis and produce at least two spores out of the zygote that you have and then the spores can be dispersed and germinated again as you complete the cycle. ASEXUAL cycle- growth of the mycelium , no fusion with other organisms, but there's still haploid spore production. Some species of fungi can do both and they'll decide depending on certain signals. But there are some fungi called imperfect- never have sex and only reproduce asexually

Fungal Reproduction

Sometimes the division is symmetric by binary fission. Sometimes it's asymmetric like in Baker's yeast which divides by budding and can also gro in filaments. Make spores when sources of nutrients are exhausted which is another similarity between bacteria and fungi, that when there is starvation, it triggers the formation of spores. Because Fungi can be diploid, 2 copies of most genes, they can reproduce sexually as well and there can be recombination. However, the DNA in the spore will always be a single copy. Spores are always haploid but sometimes produced thorugh a process where you have diploid stage. Then, you have meiosis and the resulting spore is haploid*** 1. Asexual simple cell division, growth and spread of hyphal filaments, asexual production of spores 2. Sexual sexual production of spores

Fungal Life Cycle

Spore lands in favorable environment ---> germination ---> mature mushroom ---> spores are made again---> cycle! Resistant spores

Basidiomycetes

Spores instead of being found in pods are found in these pedastools- basidium Most reproduce sexually

Genomes of Ascomycetous Yeasts

The second one is larger because it has more introns The last one can be unicellular inside the host or grow as yeast and filamentous outside. it's an opportunistic pathogen.

Ascomycetous Molds

The spores are found on the conidiophore. The spores are called conidia. Spores are a result of asexual mechanism as this fungi is imperfect, never has sex

Sexual Reproduction of Fungi

There are more than 2 sexes. But different mating type is mot a morphological difference, it's just a chemical difference. It's the type of molecule those organisms produce and the types of molecules they can sense. They'll try to mate with fungus of the same species but different mating type. The molecules that are at play in this process are called phermkones which can be called +,-,a, or alpha. Point is to attract fungus towards the source of the phermone. The hyphae will grow in the direction of where the phermone is produced.

Types of Fungi

These are not phylogenetic terms; doesn't tell you what type of fungus it is 1. Yeasts- unicellular microscopic fungi 2. Molds- filamentous microscopic fungi 3. Mushrooms- macroscopic fungi

Cryptococcus neoformans- basidiomycetous yeast

This yeast haS a capsule- important for evading immune response that's already copromised. usually the disease is caused because it's in an immune compromised patient. Genome composition is relatively similar to that of an ascomycete (sac fungi)

Rhizopus (Black Bread Mold) Asexual Life Cycle

can have either asexual or sexual life cycle. If asexual, it's just germination and growth of coenocytic hyphae and formation of sporangium in which all the spores are genetically identical and then everythig is dispered

Glomeromycetes

especially symbiotic with roots branched hyphae- tree- like structure sometimes the fungus is outside the root, sometimes inside

Robert Whittaker

fungi used to be grouped with plants, but unlike plants, they're not photosynthetic. Whittaker suggested fungi and plants are sufficiently different According to DNA sequence analysis, fungi is closer to animals and yeast can be used as a model system for study of even human biology- research of cell cycle.

Ascomycetes (sac fungi)

make spored made in structures inside pods-sac. This sac is called asci. ascocarps- fruiting bodies in which you find asci in which you find the spores Baker's yeast is in this category

Glomeromycetes' Hyphae

this specialized hyphae penetrates the root cell wall Fungus needs to make special types of interaction with the plant cells so it needs a way to penetrate it so it makes specialized hyphae called the haustoria which penetrates through the cell wall and interacts with plant cell's cytoplasm and exchanges molecules. Benefit for the plant is that the fungus is important for providing phosphate.*