Microbial Diversity: Protists and Fungi (General Biology Study Notes)

Microbiële Diversiteit – Protisten en Schimmels

Inleiding

Microbial diversity encompasses the vast variety of microscopic life forms, including protists and fungi. These organisms play essential roles in ecosystems, evolution, and the maintenance of biodiversity. This study guide summarizes key concepts from chapters 28 and 31, focusing on the biology, classification, and ecological significance of protists and fungi.

Protists

Definitie en Fylogenie van Protisten

• Protists are all eukaryotic organisms that are not animals, plants, or fungi.

• They are a paraphyletic group, meaning they do not form a single clade but are grouped for convenience.

• Protists exhibit a wide range of cellular organizations, from unicellular to multicellular forms.

Key Terms: Eukaryote, Paraphyletic, Unicellular, Multicellular

Belang van Protisten in Ecosystemen

• Protists are found in both aquatic and terrestrial environments, especially where water is present.

• They are a major component of plankton and soil food webs.

• Roles include:

  • Producers (e.g., algae via photosynthesis)

  • Predators (feeding on bacteria, fungi, or small animals)

  • Symbionts (mutualistic or parasitic relationships)

  • Saprotrophs (decomposers)

Levensstijlen en Voeding van Protisten

• Autotrophic: Obtain energy via photosynthesis (e.g., algae).

• Heterotrophic: Absorb organic material or ingest particles (fungus-like or animal-like protists).

• Mixotrophic: Combine photosynthesis and heterotrophy.

• Reproduction can be asexual or sexual, with diverse life cycles.

Example: Streptococcus tauri is a protist with a single nucleus, mitochondrion, and chloroplast, demonstrating the diversity in protist cell structure.

Voorbeeld van Mutualistische Interactie

• Some protists live in the guts of cockroaches, forming mutualistic relationships with methanogenic archaea to break down wood.

Negatieve Interacties: Oomyceten

• Oomycetes (water molds) are fungus-like protists, some of which are plant pathogens (e.g., Phytophthora infestans, the cause of potato blight).

• Oomycetes share similarities with fungi (filamentous growth, cell walls, sexual/asexual reproduction) but differ in cell wall composition (cellulose, not chitin), dominant diploid phase, and presence of flagella.

Vergelijking: Bacteria, Archaea, en Eukarya

Belangrijkste Verschillen

Trait	Bacteria	Archaea	Eukarya
Linkage of lipids	Ester	Ether	Ester
Backbone of lipids	Glycerol-3-phosphate	Glycerol-1-phosphate	Glycerol-3-phosphate
Ribosome	Bacterial	Bacterial-like	Eukaryotic
Introns	No	No	Yes
Histones	No	Yes	Yes
Genome shape	Mostly circular	Circular	Linear
Cell organization	Bacterial	Eukaryotic-like	Eukaryotic

Purpose: This table compares the fundamental differences in cell structure and genetics among the three domains of life.

De Oorsprong van Eukaryoten: Endosymbiosetheorie

Uitleg van de Theorie

• The endosymbiotic theory proposes that eukaryotic cells originated through a symbiotic relationship between ancestral prokaryotes.

• Mitochondria and chloroplasts are believed to have originated from engulfed bacteria.

Key Evidence:

• Both organelles have their own DNA, similar to bacterial genomes.

• They replicate independently of the host cell's nucleus.

• Double membranes and similarities in ribosomes to bacteria.

Equation:

$\text{Eukaryotic cell} = \text{Host cell} + \text{Endosymbiont}$

Example: The origin of mitochondria from an alpha-proteobacterium and chloroplasts from a cyanobacterium.

Schimmels (Fungi)

Eigenschappen van Schimmels

• Fungi are eukaryotic, mostly multicellular organisms with cell walls made of chitin and glucan.

• They have ergosterol in their plasma membranes (distinct from cholesterol in animals).

• Fungi are more closely related to animals than to plants.

Groei en Morfologie: Hyfen, Septa, en Mycelium

• Hyphae: Thread-like filaments that make up the body of a fungus.

• Septa: Cross-walls that divide hyphae into cells; some fungi have septate hyphae, others are coenocytic (without septa).

• Mycelium: A network of hyphae that penetrates the substrate.

Function: Hyphal growth allows fungi to efficiently explore and exploit their environment.

Levenscyclus van Schimmels

• Fungi can reproduce sexually and asexually.

• Sexual reproduction increases genetic diversity but requires more energy.

• Asexual reproduction is faster and more energy-efficient.

Advantages of Sexual Reproduction:

• Increases genetic diversity and adaptive potential.

• Eliminates negative mutations.

Disadvantages:

• Energy cost, risk of breaking up favorable gene combinations.

Groepen en Functies van Schimmels

• Chytridiomycota: Simple, often aquatic fungi with flagellated spores (zoospores).

• Zygomycetes: Form zygospores during sexual reproduction.

• Glomeromycetes: Form arbuscular mycorrhizae with plants.

• Ascomycetes: Sac fungi, produce spores in asci.

• Basidiomycetes: Club fungi, produce spores on basidia.

Functions: Saprotrophs (decomposers), mutualists (e.g., mycorrhizae, lichens), pathogens, and parasites.

Symbiose: Mutualisme en Parasitisme

• Mycorrhiza: Mutualistic association between fungi and plant roots; fungi provide water and minerals, plants provide organic carbon.

• Lichens: Symbiosis between a fungus and an alga or cyanobacterium; enables survival in harsh environments.

• Parasitism: Many fungi are plant pathogens (e.g., Magnaporthe grisea in rice, Ustilago maydis in maize) or animal pathogens (including opportunistic infections in humans).

Rol van Schimmels in Ecosystemen

• Fungi are primary decomposers of organic material, especially lignin and cellulose.

• They recycle nutrients and contribute to soil health.

• Some fungi form mutualistic relationships with animals (e.g., leaf-cutter ants cultivate fungi for food).

Belangrijke Producten van Schimmels

• Food production (e.g., Saccharomyces cerevisiae in bread and beer, Penicillium species in cheese).

• Antibiotics (e.g., penicillin from Penicillium).

• Biotechnology and genetic research (yeasts as model organisms).

Schimmeldiversiteit

• Estimated 120,000 described species; actual diversity may be much higher (up to several million species).

• Identification increasingly relies on molecular techniques (e.g., ITS sequencing).

Additional info: Some context and definitions were expanded for clarity and completeness, including the explanation of the endosymbiotic theory, fungal life cycles, and ecological roles.