Speaker A
So, we are beginning our course of lectures on mycology. And the first thing I want to tell you is that mycology is the science of fungi. The word comes from two Greek words: mykes, meaning mushroom, and logos, meaning science.
Introduction to mycology covering fungi classification, morphology, physiology, phylogenetics, and evolutionary history.
Key Takeaways
- Fungi classification integrates morphology, physiology, and genetics for accurate taxonomy.
- Phylogenetic analysis is essential for understanding evolutionary relationships among fungi.
- Fungi are a distinct monophyletic kingdom separate from plants and animals.
- Molecular clocks help date the evolutionary history of fungi.
- Microscopy and biochemical tests remain important tools alongside genomic methods.
What the video covers
- Mycology is the science of fungi, derived from Greek words meaning mushroom and science.
- Fungi classification has evolved from morphological to ecological, physiological, and phylogenetic approaches.
- Carl Linnaeus initially used structural-morphological criteria for classification, enhanced by microscopy techniques.
- Physiological-biochemical features are crucial for identifying yeast fungi species.
- Phylogenetic methods use gene sequencing, especially ribosomal genes and ITS regions, to build evolutionary trees.
- Phylogenetic trees represent hypotheses about organism relationships based on genetic data, not absolute species identity.
- The molecular evolutionary clock combines genetic mutation rates with paleontological data to estimate divergence times.
- Historically, fungi were grouped with plants as Cryptogamia but later recognized as a separate kingdom.
- Whittaker's five-kingdom system (1969) established fungi as an independent kingdom based on cell structure and nutrition.
- Fungi have unique feeding methods and diverse reproductive strategies including apical growth and budding.
Chapters
- 00:00Introduction to Mycology and Definition
- 01:06Structural-Morphological Classification
- 02:16Genomics and Phylogenetic Approaches
- 03:31Morphological Features and Taxonomy of Fungi
- 04:54Physiological-Biochemical Features in Yeasts
- 06:17Use of Ribosomal Genes in Phylogeny
- 07:33Phylogenetic Trees and ITS Regions
- 08:50Molecular Evolutionary Clock and Paleontology
- 10:03Historical Classification of Fungi
- 11:34Whittaker’s Five Kingdom Classification
Full Transcript — Download SRT & Markdown
Speaker A
And in our first lecture, we will look at the place of fungi in the living world, their structure, their general characteristics, and their origin on Earth. If we recall Carl Linnaeus, fungi are unusually complex and diverse organisms. It is a chaos
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that was difficult to classify. But science has come a long way, and various approaches and criteria for grouping organisms have been developed.
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And the first one, which Carl Linnaeus himself used, is, naturally, the structural-morphological one. That is, to characterize organisms, a comparative description of morphological features detectable visually was conducted, and in recent decades and centuries, with methods of microscopy—scanning, transmission,
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and electron microscopy—which, naturally, allowed for the identification of a mass of new, important traits. The second approach is the ecological-trophic, or physiological-biochemical, that is, an approach where the composition of specific cellular compounds is studied, their synthesis pathways, primary and
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secondary methods, ways of obtaining energy, and the range of conditions for the organisms' existence. And all these indicators are taken into account in taxonomy. And in recent decades, the phylogenetic approach has played an active, leading role, where research on
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the genes of organisms is conducted—that is, genomics approaches—and based on mathematical techniques and cladistic methods, evolutionary trees are built. These are the techniques of genosystematics. Let's look at specific examples of using cultural-morphological features in fungi. The simplest fungal organisms
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are yeasts, but even with them, we can observe growth in a liquid medium, such as the formation of a film or a ring, as shown on this slide. Analyze the shape of the cells and the shape of the
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colony. Further, using microscopy methods, analyze the life cycle and look at the formation of true mycelium or pseudomycelium. All this is the first important approach, which was actively used in the 19th century. And based on this approach, the taxonomy of
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fungi was created. Furthermore, if we take mycelial fungi, this approach is still actively used today, because morphological structures are so diverse that they often allow for species identification without using other techniques or criteria. But those same yeast fungi, with which I began my
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story, are simpler in their morphology. And therefore, for this group, physiological-biochemical features began to be used first among fungi for species identification and the description of even higher taxa. For bacterial organisms, this was, naturally, used even earlier. What are
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these features? They include the use of various sugars and the assimilation of nitrogen sources. This slide lists more than twenty or thirty such features. If we want to determine what kind of yeast fungus this is, we have to analyze a
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fairly large number of physiological-biochemical features in these fungi. In recent years, phylogenetic criteria have been actively used. They allow for the determination of organism relatedness based on genotypes—that is, the genome—rather than phenotypic similarity, which may be due to
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parallel adaptations to similar living conditions. The degree of relatedness, or more precisely, the degree of similarity or difference between organisms, is determined by the number and positions of nucleotide substitutions. To compare genomes, sequencing techniques are used to determine the sequence of base pairs in
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DNA. Analyzing an entire organism's genome is both difficult and quite expensive. Therefore, even today, the analysis of specific gene sequences is often used. For example, they use the same ribosomal genes on which ribosomal RNAs are synthesized. These genes,
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which encode protein synthesis, are highly conserved, thus allowing for the construction of macrophylogenies at the level of kingdoms, phyla, classes, and orders. However, it is very problematic to use them to identify or establish distinctions between species and genera.
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Genes controlling the synthesis of tubulin proteins, which form the microtubules of eukaryotes, are also used to build both macro- and micro-phylogenetic trees. Between ribosomal genes, there are intragenic ITS and intergenic spacer regions that do not participate in ribosome
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construction; they are not transcribed or are excised after transcription. And in these regions, more mutations are fixed, and based on them, it is possible to build meso- and micro-phylogenies at the level of families, genera, and species. On this slide, you see the regions of ribosomal
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DNA used to determine the phylogenetic position and compare species of fungi, for instance. Very often, these are the ITS1 and ITS2 regions, along with several others. Using cladistic methods, we can build phylogenetic trees like these. This slide demonstrates a
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phylogenetic tree of fungi at the phylum level and a tree where you can see the comparison and position of various species of Sordariomycetes within the class Sordariomycetes. But it is always important to remember that any constructed tree is merely a
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phylogenetic hypothesis with a certain degree of probability, describing the similarity of the primary structures of the compared semantids—that is, these informational macromolecules—but by no means of the species of organisms themselves, as Academician Antonov warned. An important approach that has
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emerged in recent years is the molecular evolutionary clock, when molecular-genetic data—that is, the estimation of the rate of incorporation of new mutant genes into species genomes and the comparative analysis of amino acid sequences of proteins—are compared with paleontological findings,
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which provides the opportunity to establish the time between the fixation of spontaneous mutations and the emergence and divergence of various taxa. This approach is actively used and will be examined by us later when we look at the evolution of fungal
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organisms on the planet and the time of their origin. And the divergence of different taxa. But at the moment, let us return to the period of the 18th century, when Carl Linnaeus was creating his Systema Naturae, and where
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exactly he placed fungi. He had a global thesis. In his classification, minerals exist, plants exist and live, animals exist, live, and feel. And, accordingly, lichens, fungi, mosses, and ferns were classified by them as Cryptogamia, that is, plants without
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visible reproductive organs. In other words, these are lower, primitive plants, fungal organisms. But less than 100 years later, the Swedish mycologist Elias Fries, considered the father of mycology, proposed separating fungi into an independent kingdom of the living world. For most biologists of
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the 19th and even the first half of the 20th century, this view found no support. Although at present, we have a situation where fungi are indeed an independent monophyletic kingdom of living organisms. The first established separation of fungi into a separate
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kingdom was carried out by Whittaker, a prominent American botanist and ecologist, in 1969. He distinguished them based precisely on structural-morphological and ecological-trophic principles. Five kingdoms: Monera (prokaryotes), Protista, Fungi (or mushrooms), Plantae, and Animalia. And here, his main
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criteria were the structure of the cell. Whether it is prokaryotic or eukaryotic, that is, having a nuclear membrane and chromosomes. Whether a cell wall exists or is absent, the composition of this cell wall—cellulose or non-cellulose—and a
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number of other features. Next, the structure of the organism: unicellular or multicellular, complex tissue or true tissue. And whether there are organs or an organ system and the different type of nutrition.
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Autotrophic, chemosynthesis or photosy
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, animals, and fungi—are eukaryotic organisms, but protists are unicellular motile microorganisms with a nucleus and nuclear membrane, autotrophs and heterotrophs. But multicellular organisms, plants, are distinguished by the principle of autotrophy. Animals are heterotrophs with a phagotrophic type of nutrition, and fungi are
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heterotrophs with an absorptive type of nutrition. Thus, according to this definition based on ecological-trophic and structural-functional traits, fungi are eukaryotic heterotrophic organisms, lacking chlorophyll, with an absorptive osmotrophic type of nutrition, which reproduce by spores, and their thallus is represented by hyphae that elongate
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through apical growth. Although, of course, there are also organisms that reproduce by budding rather than apical growth. Fungi have a special way of feeding. It differs fundamentally from other eukaryotic organisms, that is, the absorption of nutrients from the
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substrate. It is as if their digestive tract, their stomach, is turned inside out. And, accordingly, it is necessary for this branched system of hyphae, the mycelium, to be immersed in the substrate. M.
Topics:mycologyfungifungal classificationphylogeneticsmolecular clockmicroscopyyeaststaxonomygenomicsevolution
