Microbiology Study Notes: Protozoa, Fungi, Algae, and Other Eukaryotic Microbes

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Protozoa

Introduction to Protozoa

Protozoa are diverse eukaryotic microorganisms that lack cell walls and are typically unicellular. They inhabit a wide range of environments and play important roles in ecological food chains, as well as in human and animal diseases.

Motility: Protozoa move using cilia, flagella, or pseudopods.
Cell Structure: Eukaryotic, lack cell walls, some have two nuclei or contractile vacuoles.

Distribution of Protozoa

Protozoa are found in most environments, especially moist ones. They are key components of food webs and some are pathogenic to animals and humans.

Morphology of Protozoa

Unique cell morphology: some have two nuclei, mitochondria, or contractile vacuoles.
Life cycle stages: motile stage called trophozoite; dormant stage called cyst.

Nutrition of Protozoa

Most are chemoheterotrophic; some are photoautotrophic.

Reproduction of Protozoa

Asexual: binary fission, schizogony.
Sexual: gametocytes fuse to form a zygote; ciliates reproduce by conjugation.

Classification of Protozoa

Protozoa are classified by locomotion:

Sarcodina (pseudopods)
Mastigophora (flagella)
Ciliophora (cilia)
Sporozoa (nonmotile)

Genetic studies place protozoa into six taxa.

Major Groups and Examples

Amoebozoa: Move by pseudopods; includes Entamoeba (pathogen), slime molds.
Diplomonadida: Have mitosomes; includes Giardia (causes giardiasis).
Euglenozoa: Includes Euglena (photoautotrophic), kinetoplastids (Trypanosoma, Leishmania).
Alveolates: Includes ciliates (Balantidium), apicomplexans (Plasmodium, Toxoplasma), dinoflagellates (Gymnodinium, Gonyaulax, Pfiesteria).

Fungi

Introduction to Fungi

Fungi are eukaryotic organisms that include molds, mushrooms, and yeasts. They are chemoheterotrophic and have cell walls made of chitin. Fungi do not perform photosynthesis. The study of fungi is called mycology.

Significance of Fungi

Beneficial: Decomposers, help plants absorb nutrients, used in food/beverages, produce antibiotics, research tools.
Harmful: Cause diseases (mycoses), spoil food.

Morphology of Fungi

Molds: Multicellular, form hyphae (can be septate or aseptate).
Yeasts: Unicellular, some produce buds.
Dimorphic fungi: Can exist as mold or yeast forms (e.g., Histoplasma capsulatum).
Mycelium: Tangled mass of hyphae; fruiting bodies are reproductive structures.

Nutrition of Fungi

Most are saprobic (feed on decaying matter).
Some are parasitic or have modified hyphae (haustoria).
Most are aerobic; some are facultative anaerobes.

Reproduction of Fungi

Asexual: Budding (yeasts), spore formation (molds: sporangiospores, chlamydospores, conidiospores).
Sexual: Formation of sexual spores (+ and - types), dikaryon stage.

Sexual Spore Formation Steps:

Haploid cells fuse (+ and -).
Cell forms dikaryon (two nuclei).
Nuclei fuse to form diploid.
Meiosis produces haploid spores.

Classification of Fungi

Four major subgroups:

Division	Key Features	Examples
Zygomycota	Multinucleate molds, reproduce sexually/asexually, sexual spore = zygospore	Microsporidia (obligate intracellular parasites)
Ascomycota	Molds/yeasts, sexual spore = ascospore, form dikaryon	Penicillium, Claviceps purpurea, Saccharomyces, Neurospora
Basidiomycota	Mushrooms, puffballs, bracket fungi, sexual spore = basidiospore	Cryptococcus neoformans, toadstools
Deuteromycetes	Imperfect fungi, sexual stages unknown	Classification evolving

Algae

Introduction to Algae

Algae are eukaryotic photoautotrophs that produce gametes. They are classified by distribution, morphology, reproduction, and biochemical traits.

Distribution of Algae

Mostly aquatic: fresh, brackish, salt water.
Use chlorophyll and accessory pigments to absorb light.

Morphology of Algae

Unicellular or colonial; some have simple multicellular structures.

Reproduction of Algae

Unicellular: Asexual by mitosis; sexual by gametes.
Multicellular: Asexual by fragmentation; sexual by gametes or alternation of generations.

Classification of Algae

Division	Key Features	Examples
Chlorophyta (Green Algae)	Chlorophyll a and b, starch reserves, cellulose walls	Freshwater, filamentous forms
Rhodophyta (Red Algae)	Phycoerythrin pigment, cell walls with agar/carrageenan	Gelidium, Chondrus
Phaeophyta (Brown Algae)	Xanthophyll pigments, produce alginic acid	Giant kelp
Chrysophyta (Golden Algae, Diatoms)	Chrysolaminarin storage, silica cell walls	Diatoms

Water Molds

Introduction to Water Molds

Water molds are not true fungi. They are more closely related to diatoms, chrysophytes, and brown algae. Water molds are decomposers and can cause crop diseases (e.g., Great Potato Famine).

Other Eukaryotic Microbes: Parasitic Helminths and Vectors

Introduction

Although not microbes, parasitic helminths and arthropod vectors are important in microbiology due to their role in disease transmission.

Helminths

Parasitic worms: Found in human body fluids; can be mechanical or biological vectors.

Arthropod Vectors

Arachnids: Ticks and mites; transmit bacterial, viral, protozoan diseases (e.g., Lyme disease).
Insects: Fleas, lice, mosquitoes, kissing bugs; transmit various diseases (e.g., plague, typhus, malaria, Chagas disease).

Summary Table: Human Pathogens by Group

Group	Pathogen	Disease
Protozoa	Trichomonas vaginalis	STD
Protozoa	Giardia	Giardiasis (severe diarrhea)
Protozoa	Kinetoplastids: Trypanosoma, Leishmania	Trypanosomiasis, Leishmaniasis
Protozoa	Balantidium	Amoebic dysentery
Protozoa	Apicomplexans: Plasmodium, Toxoplasma	Malaria, toxoplasmosis
Protozoa	Dinoflagellates: Gymnodinium, Gonyaulax, Pfiesteria	Produce neurotoxins
Protozoa	Amoebozoa: Naegleria, Acanthamoeba, Entamoeba	Brain infections, amoebic dysentery
Fungi	Microsporidia	Immunocompromised disease
Fungi	Ascomycota: Claviceps purpurea	Ergot poisoning, hallucinations
Fungi	Ascomycota: Penicillium	Antibiotic production
Fungi	Basidiomycota: Cryptococcus neoformans	Fungal meningitis
Lichens	Fungi + photosynthetic microbes	Environmental contributions

Key Terms and Definitions

Trophozoite: Motile feeding stage of protozoa.
Cyst: Dormant, resistant stage of protozoa.
Hyphae: Filamentous structures in molds.
Mycelium: Mass of hyphae.
Saprobe: Organism that feeds on decaying matter.
Dikaryon: Fungal cell with two nuclei.
Zygospore, Ascospore, Basidiospore: Sexual spores of fungi.
Lichen: Symbiotic partnership between fungus and photosynthetic microbe.

Important Equations and Processes

Fungal Sexual Reproduction:

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