The Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Fungi

Fungi are a diverse group of eukaryotic organisms studied in the field of mycology. They play essential roles in decomposition and nutrient cycling, and can be medically or economically significant.

• Chemoheterotrophs: Obtain energy and carbon from organic compounds.

• Decompose organic matter: Important in recycling nutrients.

• Aerobic or facultative anaerobic: Most molds are aerobic; most yeasts are facultative anaerobes.

• Non-motile: Fungi do not possess structures for movement.

Fungal Structures

• Yeasts: Nonfilamentous, unicellular fungi.

  • Budding yeasts: Divide unevenly, producing a bud that eventually detaches.

  • Fission yeasts: Divide evenly to produce two new cells.

• Dimorphic fungi: Can exist as both yeast-like and mold-like forms, depending on environmental conditions.

Representative Asexual Spores

• Conidia: Asexual spores formed in chains at the end of conidiophores (e.g., Aspergillus niger).

• Arthroconidia: Formed by fragmentation of hyphae.

• Blastoconidia: Formed from the buds of a parent cell (e.g., Candida albicans).

• Chlamydoconidium: Thick-walled cells within hyphae.

• Sporangiospores: Formed within a sporangium (e.g., Rhizopus stolonifer).

Fungal Nutritional Adaptations

• Grow best at pH 5.

• Resistant to osmotic pressure; can grow in high sugar and salt concentrations.

• Can grow in low moisture environments.

• Can metabolize complex carbohydrates.

• Require less nitrogen than bacteria.

Medically Important Fungi

• Zygomycota: Includes Rhizopus stolonifer.

• Microsporidia: Obligate intracellular parasites; lack mitochondria.

• Ascomycota: Includes Saccharomyces cerevisiae (baker's yeast), Claviceps purperea (ergot).

• Basidiomycota: Includes Cryptococcus neoformans, a plant pathogen.

Fungal Diseases (Mycoses)

• Systemic mycoses: Affect deep tissues and organs.

• Subcutaneous mycoses: Occur beneath the skin.

• Cutaneous mycoses: Affect hair, skin, and nails.

• Superficial mycoses: Localized to hair shafts.

• Opportunistic mycoses: Harmless fungi become pathogenic in compromised hosts.

Economic Uses of Fungi

• Aspergillus niger: Production of citric acid.

• Aspergillus terreus: Production of statins (cholesterol inhibitors).

• Saccharomyces cerevisiae: Used in bread, wine, and hepatitis B vaccine production.

• Trichoderma: Produces cellulase.

• Taxomyces: Produces taxol (anticancer drug).

• Tolypocladium inflatum: Produces cyclosporine (immunosuppressant).

• Coniothyrium minitans: Biocontrol agent against crop fungi.

• Paecilomyces: Used to kill termites.

Algae

Algae are a diverse group of photosynthetic eukaryotes, important for their ecological roles and economic uses.

• Not a taxonomic group.

• Unicellular or filamentous photoautotrophs.

• Lack roots, stems, and leaves.

• Mostly aquatic; found in various water habitats.

• All reproduce asexually; multicellular algae may reproduce sexually or by fragmentation.

Diatoms

• Pectin and silica cell walls.

• Unicellular or filamentous.

• Store energy from photosynthesis as oil.

• Produce domoic acid, which can cause neurological disease.

Dinoflagellates

• Cellulose in plasma membrane.

• Unicellular.

• Produce neurotoxins (saxitoxins) that cause paralytic shellfish poisoning.

Oomycota (Water Molds)

• Cellulose cell walls.

• Chemoheterotrophic.

• Decomposers and plant parasites.

• Phytophthora infestans caused the Irish potato blight.

• P. cinnamoni infects Eucalyptus; P. ramorum causes "sudden oak death".

Roles of Algae in Nature

• Fix CO2 into organic molecules.

• Produce 80% of Earth's O2.

• Algal blooms can release toxins or consume O2 when they die.

• Oil production.

• Symbionts with animals.

Protozoa

Protozoa are unicellular eukaryotes with complex life cycles, found in water and soil. Some are normal microbiota, while others cause disease.

• Feeding and growing form is a trophozoite.

• Asexual reproduction by fission, budding, or schizogony (multiple fission).

• Sexual reproduction via conjugation.

• Cysts allow survival in harsh conditions.

Characteristics of Protozoa

• Require water for survival.

• Many have a protective pellicle.

• Ciliates use cilia to direct food into a cytosome.

• Amebae phagocytize food.

• Food is digested in vacuoles; wastes eliminated via anal pore.

Medically Important Protozoa

• Amebae: Move by pseudopods; includes Entamoeba histolytica (causes amebic dysentery), Acanthamoeba (infects corneas), Balamuthia (causes encephalitis).

• Apicomplexa: Nonmotile, obligate intracellular parasites; includes Toxoplasma gondii (fetal infections), Cryptosporidium (waterborne illness), Plasmodium (malaria).

• Ciliates: Move by cilia; Balantidium coli causes dysentery.

• Diplomonads: No mitochondria, multiple flagella.

• Parabasalids: Undulating membrane, no cyst stage.

• Euglenozoa: Photoautotrophs or facultative chemotrophs; hemoflagellates transmitted by blood-feeding insects.

Helminths

Helminths are multicellular parasitic worms, classified into two phyla: Platyhelminthes (flatworms) and Nematoda (roundworms).

• Specialized to live in hosts; may lack digestive system, have reduced nervous system, and complex reproductive system.

• Life cycle may involve separate sexes (dioecious) or both reproductive systems in one animal (monoecious).

• Life stages: egg → larva(e) → adult.

Hosts

• Definitive host: Supports adult or sexually reproductive form.

• Intermediate host: Supports immature or nonreproductive forms.

Platyhelminths

• Trematodes (flukes): Flat, leaf-shaped; ventral and oral suckers; absorb food through cuticle.

• Cestodes (tapeworms): Scolex (head with suckers), proglottids (body segments with reproductive organs), absorb food through cuticle.

• Taenia solium: Pork tapeworm; humans can be definitive or intermediate hosts.

• Echinococcus granulosus: Causes hydatid cysts in liver or lungs.

Nematodes

• Cylindrical, complete digestive system.

• Dioecious; free-living and parasitic.

• Eggs infective for humans: Ascaris lumbricoides (intestinal), Baylisascaris procyonis (raccoon roundworm), Trichuris trichiura (whipworm), Enterobius vermicularis (pinworm).

• Larvae infective for humans: Strongyloides (reemerging), Necator americanus & Ancylostoma duodenale (hookworms), Dirofilaria immitis (heartworm).

Arthropods as Vectors

Arthropods are animals with segmented bodies, hard exoskeletons, and jointed legs. Some act as vectors, carrying pathogenic microorganisms.

• Arachnida: Eight legs.

• Crustacea: Four antennae.

• Insecta: Six legs.

Additional info: These notes cover the structure, function, and medical importance of eukaryotic microorganisms, including fungi, algae, protozoa, and helminths, as well as their ecological and economic roles.