General living conditions
The physiological features of fungi determine their ubiquitous distribution in nature. These microorganisms are especially common in soil, which serves as a natural reservoir for them.
- Nutrition and respiration: All fungi are heterotrophs. This means they cannot independently synthesize organic substances from inorganic ones and must obtain them preformed from the outside. With respect to molecular oxygen, fungi are divided into two groups: aerobes (require oxygen) and facultative anaerobes (can survive and grow even in the absence of oxygen).
- Temperature regime: Microorganisms of this group can survive in a very wide range of temperatures. However, the optimal conditions for their vital activity are an environment warmed to 25–30 °C.
- Reproduction: The life cycle of fungi involves two options for reproduction: sexual and asexual. The choice of pathway depends on the specific species and environmental conditions.
Symbiotic relationships
Fungi actively enter into mutually beneficial relationships with other living organisms. In nature, two forms of such symbiosis are most pronounced:
- Lichens. This is a complex symbiosis of fungi and blue-green algae. In this union, roles are strictly distributed: the fungal part is responsible for absorbing water and water-soluble mineral substances from the environment. In turn, the alga engages in synthesizing the necessary organic compounds, which it shares with the fungus.
- Mycorrhiza. This is a close symbiotic interaction between the fungal mycelium and the root system of higher plants. Such coexistence improves the nutrition of both organisms.
Laboratory cultivation
Growing fungi in laboratory conditions has a number of significant differences from cultivating bacteria.
- Growth rates: The process takes significantly more time. While a day is sufficient for most fungi-like bacteria, visible growth of fungi on artificial media appears only after several days.
- Nutrient media: Specialized media rich in carbohydrates are used for successful cultivation. These include: wort agar, liquid unhopped wort, classical Sabouraud medium, and Czapek medium.
- Biological assays: In complex diagnostic cases, in addition to inoculations on media, laboratory practice allows the use of experimental animals for biological assays.
The phenomenon of dimorphism
One of the most important adaptive features of certain fungal species is dimorphism.
This phenomenon is defined as the ability of a microorganism to radically change its morphological form depending on current habitat conditions. There are two main forms of existence for dimorphic fungi:
- Filamentous (mycelial) form: Typical for existence in the external (surrounding) environment. It is an intertwining of hyphae.
- Yeast (yeast-like) form: This form is formed exclusively in vivo — that is, directly inside the human or animal organism during the development of an infectious process.
Briefly: answers to topical questions
What is the difference between mycorrhiza and lichens?
The main difference lies in the fungus's symbiotic partner and the distribution of roles.
| Characteristic | Mycorrhiza | Lichens |
|---|---|---|
| Essence of symbiosis | Symbiosis of fungal mycelium with the roots of higher plants | Symbiosis of fungi and blue-green algae |
| Value | Stimulates and improves plant growth | The fungus absorbs water and soluble substances, while the alga synthesizes organic compounds |
What types of asexual and sexual reproduction exist in fungi?
Fungi have various mechanisms of sexual and asexual reproduction that form different morphological stages.
- Sexual reproduction (teleomorphs) occurs with the formation of gametes, sexual spores, and other sexual forms.
- Asexual reproduction (anamorphs) is carried out through budding, hyphal fragmentation, or the formation of asexual spores.
The sexual method is characteristic of perfect fungi, whereas imperfect and yeast-like fungi reproduce exclusively by asexual means. In yeasts, asexual reproduction occurs by budding or division.
To remember the main nutrient media for fungi, use the rule of three "S"s: Wort (liquid and agar), Sabouraud. Plus Czapek medium.
Class and exam questions
How fast do fungi grow on nutrient media compared to bacteria?
Fungi grow significantly slower. They require several days to form full-fledged colonies, whereas 18–24 hours are sufficient for many bacteria.
What does the term "dimorphism" mean in mycology?
This is the ability of a fungus to change its shape (from filamentous in the external environment to yeast-like in vivo upon infection of a host) depending on habitat conditions.
What is the role of the fungus within a lichen?
In symbiosis with blue-green algae, the fungus takes on the function of absorbing water and soluble inorganic substances, providing them to its partner.
What else to study on this topic
- Mechanisms of sexual and asexual reproduction in fungi
- Detailed composition of Sabouraud and Czapek media
- Pathogenesis of the transition from mycelial to yeast form in vivo
- Significance of mycorrhiza for agriculture
- Methodology for setting up biological assays on laboratory animals
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