Overview
This lecture introduces major groups of microorganisms, the branches of microbiology that study them, methods used to observe them, and systems for classifying and naming microbes.
Types of Microorganisms
- Microorganisms are divided into categories: bacteria, archaea, fungi, protozoa, helminths, algae, and viruses.
- Bacteria and archaea are prokaryotic (no nucleus or organelles) and always unicellular.
- Fungi are eukaryotic and can be unicellular (yeasts) or multicellular (molds).
- Protozoa are unicellular eukaryotes, grouped by structure, not taxonomy.
- Helminths are multicellular eukaryotic organisms, always multicellular.
- Algae are eukaryotic and can be unicellular or multicellular.
- Viruses are acellular, non-living entities.
Branches of Microbiology
- Bacteriology studies bacteria and archaea.
- Mycology studies fungi.
- Parasitology studies protozoa and helminths.
- Phycology studies algae.
- Virology studies viruses.
Viewing Microorganisms
- Bacteria and archaea: often visible with light microscopy.
- Fungi and protozoa: visible with light microscopy.
- Helminths: usually visible to the naked eye, occasionally need light microscopy.
- Algae: visible to the naked eye or with light microscopy.
- Viruses: normally require electron microscopy to be seen.
Classification Systems
- Whitaker's five-kingdom system uses structural/ecological traits: Monera (prokaryotes), Protista (unicellular eukaryotes), Fungi, Plantae, Animalia.
- Taxonomy is artificial and can be based on different criteria.
- Woese-Fox system (current standard) classifies life by genetic similarities in the 16S rRNA gene.
- Woese defined three domains: Bacteria, Archaea, and Eukarya, all derived from a last universal common ancestor.
- Archaea and Eukarya are genetically closer to each other than to Bacteria.
Naming Microorganisms
- Binomial nomenclature assigns two names: genus and species (e.g., Staphylococcus aureus).
- Viruses have a more complex and less standardized naming system.
Key Terms & Definitions
- Prokaryotic — Cells lacking a nucleus or membrane-bound organelles (e.g., bacteria, archaea).
- Eukaryotic — Cells with a nucleus and membrane-bound organelles.
- Acellular — Not composed of cells (e.g., viruses).
- Binomial nomenclature — Two-part scientific naming method using genus and species.
- 16S rRNA gene — A gene used for genetic classification and evolutionary studies of organisms.
Action Items / Next Steps
- Be prepared to identify and characterize different microbe groups for future questions.
- Review classification systems and practice naming microbes using binomial nomenclature.