Overview
This lecture introduces the primary types of microorganisms, their characteristics, and their classification among the domains of life, highlighting differences in structure, function, and roles in human health.
Microorganism Basics and Size
- Most microorganisms are unicellular and require magnification to view.
- Objects must be about 100 micrometers (μm) to be seen without a microscope.
- Typical animal cells are ~10 μm, bacteria ~1 μm, and viruses ~0.1 μm (100 nm).
- Microorganisms vary in size, structure, habitat, and metabolism.
Domains and Classification
- Microorganisms exist within three domains: Archaea, Bacteria, and Eukarya.
- Bacteria and Archaea are prokaryotes (cells lack a nucleus).
- Eukarya includes all eukaryotes (cells contain a nucleus).
- Viruses and prions are acellular and not classified in any domain.
Prokaryotic Microorganisms
- Bacteria are ubiquitous, mostly harmless, some pathogenic, and have peptidoglycan-based cell walls.
- Bacterial shapes: coccus (spherical), bacillus (rod), spirillum/spirochete/vibrio (curved).
- Bacteria have diverse metabolisms (photosynthetic or nonphotosynthetic).
- Archaea are unicellular, exist in extreme environments, lack peptidoglycan in cell walls, and are not known to cause disease.
Eukaryotic Microorganisms
Protists
- Protists include algae and protozoa, neither plants, animals, nor fungi.
- Algae can be unicellular/multicellular, are photosynthetic, and have cellulose cell walls.
- Protozoa are diverse, may move via cilia, flagella, or pseudopods, and can be pathogenic or free-living.
Fungi
- Fungi include unicellular yeasts and multicellular molds; cell walls are usually chitin-based.
- Yeasts are involved in fermentation and can cause disease.
- Molds decompose organic matter and can produce allergens or antibiotics.
Helminths
- Helminths are multicellular parasitic worms; adult forms are visible, but eggs/larvae are microscopic.
- Studied in microbiology due to disease mechanisms involving microscopic stages.
Viruses and Prions
- Viruses are acellular entities made of protein and nucleic acid (DNA or RNA), requiring host cells to reproduce.
- Prions are infectious proteins without genetic material, causing diseases like Creutzfeldt-Jakob disease (CJD).
Microbiology as a Field
- Subfields: bacteriology, mycology, protozoology, parasitology, virology, and immunology.
- Clinical, environmental, and applied microbiology are specializations.
Ethics in Microbiology
- Research must follow ethical standards: informed consent, integrity, respect for rights, and proper review processes.
Key Terms & Definitions
- Microorganism — Organism too small to be seen without a microscope.
- Prokaryote — Cell lacking a nucleus (Bacteria, Archaea).
- Eukaryote — Cell with a nucleus (Protists, Fungi, Plants, Animals).
- Virus — Acellular infectious agent with protein coat and genetic material.
- Prion — Infectious protein causing neurodegenerative diseases.
- Helminth — Parasitic worm, some stages microscopic.
- Pathogen — Microbe capable of causing disease.
Action Items / Next Steps
- Review Table 1.1 on units of length used in microbiology.
- Explore the interactive website to compare microbe sizes.
- Answer review questions to test understanding of microorganism types and characteristics.