Fungi: Roles in Environment and Industry

Fungi: Key Roles in the Environment and Industry

• Fungi break down complex organic materials (like dead plants and animals) into simpler compounds, playing a crucial role in nutrient cycling.
• They are a major cause of disease in plants, invading leaves through openings called stomata.
• Fungi also cause diseases in animals and humans.
• Yeasts, a type of fungi, are essential for fermentation processes like making bread, wine, and beer.
• Fungi are involved in the production of various foods like cheeses, soy sauce, and sufu.
• Fungi are vital for commercial production of organic acids (citric and gallic acids) and certain drugs like ergometrine and cortisone.
• Fungi are important in the production of antibiotics (penicillin, griseofulvin) and the immunosuppressive drug cyclosporin.

Fungal Structures

• The fungal body, also known as the thallus, varies in structure and size, ranging from single-celled yeasts to multicellular molds, puffballs, and mushrooms.
• Typically, fungal cells have a cell wall made of chitin, a strong and flexible polysaccharide composed of N-acetylglucosamine residues.

Yeasts

• Yeasts are single-celled fungi with a single nucleus.
• They reproduce by budding (asexual) and spore formation (sexual).
• Each bud that separates can develop into a new yeast cell.
• Yeast cells are generally spherical or egg-shaped and lack flagella but contain most eukaryotic organelles.

Molds

• Mold thalli consist of long, branched, thread-like filaments called hyphae, which form a tangled mass known as mycelium.
• Some fungi have hyphae without cross-walls, called coenocytic or aseptate hyphae.
• Other fungi have cross-walls, called septa, with pores that allow cytoplasmic streaming. These hyphae are called septate hyphae.
• Hyphae are composed of an outer cell wall and an inner lumen, which contains the cytosol and organelles.
• The filamentous nature of hyphae provides a large surface area for efficient nutrient absorption.

Dimorphic Fungi

• Many fungi, especially those causing diseases in humans and animals, are dimorphic, meaning they exist in two forms.
• Dimorphic fungi can switch between a yeast form (in the animal) and a mold/mycelial form (in the external environment) in response to environmental changes (nutrients, CO2, temperature). This shift is called the YM shift.

Fungal Nutrition and Metabolism

• Fungi thrive in dark, moist habitats with abundant organic material.
• Most fungi are saprophytes, obtaining nutrients from dead organic matter.
• They are chemoorganoheterotrophs, using organic compounds for carbon, electrons, and energy.
• Glycogen is the primary storage polysaccharide in fungi.
• Fungi generally use carbohydrates (glucose or maltose) and nitrogenous compounds for synthesizing amino acids and proteins.
• Many fungi are aerobic, but some yeasts are facultatively anaerobic, meaning they can ferment to obtain energy. Obligately anaerobic fungi are found in the rumen of cattle.
• Fungal fermentations are crucial in industrial processes, such as ethanol production for beer and wine.

Fungal Ecology

• Along with bacteria, fungi are major decomposers in the biosphere, responsible for breaking down organic matter.
• Fungi are unique in their ability to break down cellulose and lignin, complex plant components.
• Fungi form symbiotic relationships with various organisms:
• Obligate symbiosis: Essential for fungal survival.
• Facultative symbiosis: Not essential for fungal survival.

Types of Symbiotic Relationships

• Pathogens and parasites: Benefit at the expense of the host.
• Commensals: Benefit one partner but do not harm or benefit the other.
• Mutualistic relationships: Benefit both partners.

Endophytic Fungi

• Endophytic fungi live inside the intercellular spaces of plants.
• They can protect their host from herbivores by producing toxins, making the host less palatable to herbivores.
• Ryegrass is more resistant to aphid feeding in the presence of endophytes.

Lichens

• Lichens represent a symbiotic relationship between a specific ascomycete fungus and either green algae or cyanobacteria.

Fungal Preservation Techniques

• Stock cultures are transferred to fresh media at intervals and stored at 4°C to preserve their viability.
• Agar slants are commonly used, but contamination must be avoided.
• Long-term preservation methods aim to maintain the viability and genetic stability of fungal cultures.
• Preservation methods can be categorized into two groups:
• Metabolically inactive:
• Cryopreservation: Freezing cells or tissues at very low temperatures (-196°C).
• Drying methods: Spin freeze-drying, vacuum drying.
• Metabolically active:
• Culturing at low temperatures.
• Storage in liquid nitrogen.
• Cryoprotectant agents.

Mycotoxins

• Mycotoxins are toxic secondary metabolites produced by certain fungi.
• Mycotoxins can contaminate food and feed, posing risks to human and animal health.
• Rot disease in peanuts is caused by Aspergillus niger.
• Aspergillus species produce aflatoxin B1, a potent carcinogen associated with liver cancer.

Importance of Fungi

• Pharmaceuticals: Production of antibiotics (e.g., penicillin) and enzymes.
• Agriculture: Biopesticides (e.g., Bt cotton), biofertilizers, and biocontrol agents.

Protozoa: Key Features and Reproduction

• Protozoan cells contain at least one eukaryotic nucleus.
• Many protozoans have multiple nuclei, like ciliates.
• Ciliates have two distinct nuclei: a large macronucleus (controls metabolism and regeneration) and a small micronucleus (involved in reproduction).
• Reproduction in protozoa is primarily asexual.
• Many can also reproduce sexually.
• Parasitic protozoa may have an asexual phase in one host and a sexual phase in another (e.g., Plasmodium).

Asexual Reproduction in Protozoa

• Binary fission: Simple cell division.
• Multiple fission: Division into multiple daughter cells.
• Budding: Formation of buds that detach and grow.

Sexual Reproduction in Protozoa

• Involves the fusion of two gametes.
• Conjugation occurs in ciliates.

Control of Microorganisms

• Physical, chemical, and biological methods are used to inhibit or prevent microbial growth.
• Physical methods: Heat, radiation, filtration.
• Chemical agents: Disinfectants, antiseptics, antibiotics.
• Biological agents: Bacteria, fungi, viruses.
• Antimicrobial activity is influenced by factors like:
• Concentration of the agent.
• Temperature.
• pH.
• Presence of organic matter.

Mechanisms for Acquiring Resistance

• Microorganisms can develop resistance to antimicrobial agents through various mechanisms:
• Mutation: Changes in the microbial DNA.
• Horizontal gene transfer: Sharing of resistance genes between microbes.
• Reduced permeability: Altered cell membrane prevents drug entry.
• Drug inactivation: Production of enzymes that break down or modify the drug.
• Target modification: Alteration of the drug's target site within the microbe.

MRSA (Methicillin-resistant Staphylococcus aureus), VRSA (Vancomycin-resistant S. aureus), and VRE (Vancomycin-resistant Enterococcus)

• MRSA, VRSA, and VRE are clinically significant antibiotic-resistant bacteria.
• They are resistant to multiple antibiotics, including methicillin and vancomycin.
• MRSA and VRSA harbor several resistance genes, including those on plasmids which can transfer to other bacteria.
• VRE, particularly Enterococcus faecalis, accounts for a significant proportion of vancomycin-resistant bacteria.
• Clostridium difficile is a superinfection pathogen that can establish itself in the intestinal tract after antibiotic therapy.
• C. difficile is resistant to antibiotics, making infections difficult to treat.

Guidelines for Extending the Useful Life of Antimicrobials

• To combat the rising threat of antimicrobial resistance, guidelines are implemented for:
• Appropriate use: Prescribing antibiotics only when necessary.
• Complete courses: Finishing entire antibiotic regimens to ensure eradication of the infection.
• Infection prevention: Implementing measures to prevent the spread of infections.
• Development of new drugs: Researching and developing new antimicrobial agents to overcome resistance.

Antifungal Agents

• Human fungal infections have significantly increased in recent years.
• Fungal infections are more challenging to treat than bacterial infections due to:
• Slow growth: Fungi grow slower than bacteria.
• Tissue penetration: Fungal infections often occur in tissues difficult for antimicrobial agents to reach.
• Prolonged treatment: Therapy for fungal infections typically requires extended treatment.
• Antifungal agents target fungal-specific components:
• Chitin: Fungal cell walls contain chitin, which is absent in human cells.
• Ergosterol: Fungal cell membranes contain ergosterol, which is distinct from cholesterol in human cell membranes.

Fungal Infections

• Two major categories of fungal infections:

   - **Superficial:** Affecting the skin, hair, or nails:
  

• Dermatomycoses: Caused by fungi like Epidermophyton, Trichophyton, and Microsporum.

• Candidiasis (yeast infections) : Caused by the genus Candida, affecting skin, mouth, GI tract, or vagina.

   - **Systemic:** Impacting internal organs and systems: 
  

• Candidiasis, Cryptococcosis, Aspergillosis, Blastomycosis, Histoplasmosis, Coccidioidomycosis, Paracoccidioidomycosis, etc.