Protists, Fungi, Helminths, and Arthropods: Microbiology Study Notes

Economic Effects of Fungi

Overview of Fungal Impacts

Fungi have significant economic impacts, both beneficial and harmful. They play roles in industrial production, food spoilage, and disease.

• Aspergillus niger: Production of citric acid.

• Aspergillus oryzae: Fermentation of soybeans for soy sauce.

• Trichoderma: Cellulase production (used in biofuels, textiles).

• Taxomyces: Taxol (anti-cancer drug) production.

• Entomophaga: Biological control of pests.

• Coniothyrium minitans: Kills crop fungi (biocontrol agent).

• Paecilomyces: Kills termites.

Protists

Introduction to Protists

Protists are a diverse group of eukaryotes, including unicellular, multicellular, and colonial organisms. They can be autotrophic or heterotrophic and reproduce sexually or asexually.

• Many have a cell wall or lack one.

• Examples: Algae, Slime molds, Protozoa.

Characteristics of Protozoa

Protozoa are unicellular eukaryotes that require water and often inhabit soil or aquatic environments.

• Many are parasitic or predatory and specialized for feeding.

• Some have complex life cycles with sexual and asexual reproduction.

• Motility is achieved via flagella, cilia, or pseudopodia.

Protozoan Diversity and Pathogenicity

There are thousands of species of protozoa, some of which are serious medical concerns, while others are harmless. Pathogenic protozoa cause diseases such as malaria and giardiasis.

• Examples of diseases: Plasmodium (malaria), Trichomonas (vaginitis), Giardia (giardiasis).

Protozoan Life Cycle

Protozoa often have complex life cycles, including:

• Trophozoite stage: Actively feeding, growing.

• Cyst stage: Dormant, resistant to harsh conditions, or schizogony (multiple fission).

• Some produce a cyst to survive adverse conditions.

Classification by Motility

Protozoa are classified based on their mode of movement:

• Amoeboid (pseudopods)

• Flagellated (flagella)

• Ciliated (cilia)

• Spore-forming (nonmotile)

Medically Important Protozoa

Several protozoa are medically significant due to their role in human disease.

• Feeding grooves (Excavata): Move by flagella/undulating membrane. Examples: Giardia lamblia (giardiasis), Trichomonas vaginalis (vaginitis), Trypanosoma (sleeping sickness).

• Amoebozoa: Move by pseudopodia. Examples: Entamoeba histolytica (amoebic dysentery), Acanthamoeba (keratitis).

• Apicomplexa: Nonmotile, complex life cycles. Examples: Plasmodium (malaria), Toxoplasma gondii (toxoplasmosis), Cryptosporidium (diarrhea).

• Ciliates: Move by cilia. Example: Balantidium coli (balantidiasis).

Spore-Forming Protozoans (Apicomplexa)

Apicomplexa are the largest phyla of protozoans, characterized by complex life cycles and spore formation.

• Motility achieved during flagellate, cilia, or pseudopodia.

• Life cycle includes sexual and asexual stages.

• Key genera: Plasmodium (malaria), Toxoplasma (toxoplasmosis), Cryptosporidium (diarrhea).

Animals

Introduction to Animals

Animals are multicellular organisms that do not carry out photosynthesis and obtain organic nutrients from other sources. They include parasitic worms (helminths) and arthropods.

• Estimated 7.5 million animal species.

Helminths (Parasitic Worms)

Helminths are parasitic worms with complex life cycles, often spread in microscopic forms. WHO estimates half the world's population is infected with some type of helminth.

• Two phyla: Platyhelminthes (flatworms) and Nematoda (roundworms).

• Specialized for host invasion: digestive system, movement, reproduction.

• Life cycle may include egg, larval, and adult stages or Monoecious (hermaphroditic) vs. Dioecious (separate sexes).

Platyhelminthes

• Trematodes (flukes): Flat, leaf-shaped; ventral/oral suckers; absorb food through cuticle. Examples: Paragonimus (lung fluke), Schistosoma (blood fluke).

• Cestodes (tapeworms): Segmented body (proglottids), absorb food through cuticle. Examples: Taenia (beef/pork tapeworm), Echinococcus (hydatid disease).

Nematodes

• Roundworms: Cylindrical, complete digestive system; dioecious (males have spicules).

• Examples: Ascaris lumbricoides, Enterobius vermicularis (pinworm), Trichuris (whipworm), Necator (hookworm), Trichinella (trichinosis).

Arthropods as Vectors

Arthropods are animals with segmented bodies, hard exoskeletons, and jointed legs. Some act as vectors, transmitting disease.

• Classes: Arthropoda (phylum), Crustacea (crabs, crayfish), Insecta (six legs).

• Definitive host: Microbe's sexual reproduction occurs in vector.