Chapter 1: The Microbial World and You – Structured Study Notes

Chapter 1: The Microbial World and You

Scientific Nomenclature: Genus and Species

Microorganisms are classified using a binomial nomenclature system, which provides a universal method for identifying and naming organisms.

• Binomial Nomenclature: Developed by Carl Linnaeus; uses two names: Genus (capitalized) and species (lowercase).

• Genus: A broader group; e.g., Escherichia.

• Species: A specific organism within the genus; e.g., Escherichia coli.

• Purpose: Universal, precise identification of organisms.

• Application: Scientific names can describe an organism, honor a researcher, or identify the habitat of a species.

Major Groups of Microorganisms

Microorganisms are classified into several major groups based on cellular structure, metabolism, and genetic characteristics.

Bacteria

• Cell Type: Prokaryotic, unicellular.

• Shapes: Bacillus (rod-shaped), coccus (spherical), spiral.

• Cell Wall: Contains peptidoglycan.

• Reproduction: Binary fission.

• Nutrition: Can use organic/inorganic chemicals or photosynthesis.

• Motility: Many bacteria use flagella.

Archaea

• Cell Type: Prokaryotic, unicellular.

• Cell Wall: If present, lacks peptidoglycan.

• Habitat: Extreme environments (e.g., methanogens, extreme halophiles, extreme thermophiles).

• Pathogenicity: Not known to cause disease in humans.

Fungi

• Cell Type: Eukaryotic; can be unicellular (yeasts) or multicellular (molds).

• Cell Wall: Contains chitin.

• Nutrition: Absorbs organic chemicals.

• Reproduction: Can reproduce sexually or asexually.

• Examples: Yeasts (oval, unicellular), molds (filamentous).

Protozoa

• Cell Type: Eukaryotic, unicellular.

• Motility: Move by pseudopods, flagella, or cilia.

• Nutrition: Absorbs or ingests organic chemicals.

• Reproduction: Can reproduce sexually or asexually.

• Parasitism: Some are parasitic.

Algae

• Cell Type: Eukaryotic, mostly multicellular.

• Nutrition: Photosynthetic; produce oxygen and carbohydrates.

• Cell Wall: Contains cellulose.

• Reproduction: Can reproduce sexually or asexually.

• Ecological Role: Important in food production and environmental balance.

Helminths

• Cell Type: Multicellular, eukaryotic parasitic worms.

Viruses

• Cell Type: Acellular; not cells.

• Structure: Consist of DNA or RNA core surrounded by a protein coat.

• Replication: Can only replicate inside a living host cell.

• Pathogenicity: Cause infectious diseases.

Impact of Microbes on Human Life

Microbes play essential roles in health, industry, and the environment, but can also be harmful.

• Beneficial Effects: Normal microbiota, vitamin production, food production (bread, cheese), medicine (antibiotics, vaccines), environmental recycling.

• Harmful Effects: Cause infectious diseases, spoilage of food, produce toxins.

• Key Point: Most microbes are beneficial or harmless.

Historical Contributions to Microbiology

Observations and experiments by early scientists laid the foundation for microbiology.

• Robert Hooke: Observed cells in cork; published Micrographia.

• Antonie van Leeuwenhoek: First to observe living microorganisms; called them "animalcules".

• Francesco Redi: Disproved spontaneous generation (meat and maggots experiment).

• Louis Pasteur: Germ theory, pasteurization, fermentation.

• Ignaz Semmelweis: Handwashing reduces infection.

• Joseph Lister: Antiseptic surgery.

• Robert Koch: Koch's postulates; identified specific microbes causing specific diseases.

• Alexander Fleming: Discovered penicillin.

Spontaneous Generation vs. Biogenesis

Early debates focused on the origin of life and the role of microbes.

• Spontaneous Generation: Life arises from nonliving matter (e.g., maggots from meat).

• Biogenesis: Living cells arise only from existing life.

• Key Experiment: Pasteur's swan-neck flask disproved spontaneous generation.

Koch's Postulates

Koch's postulates are criteria used to establish a causative relationship between a microbe and a disease.

1. The microbe must be present in all cases of the disease.

2. The microbe must be isolated and grown in pure culture.

3. The cultured microbe must cause disease in a healthy host.

4. The microbe must be re-isolated from the experimentally infected host.

Significance: Foundation of medical microbiology.

Three Domains of Life

Organisms are classified into three domains based on genetic and cellular differences, as proposed by Carl Woese.

Domain	Cell Type	Examples
Bacteria	Prokaryotic	Cell wall contains peptidoglycan
Archaea	Prokaryotic	If cell wall present, lacks peptidoglycan
Eukarya	Eukaryotic	Protists, fungi, plants, animals

Key Definitions

• Normal Microbiota: Microbes normally present in the body.

• Biofilms: Microbial communities attached to surfaces.

• Bacteria: Prokaryotic, unicellular organisms.

• Fungi: Eukaryotic, absorb nutrients.

• Algae: Photosynthetic eukaryotes.

• Protozoa: Unicellular, motile eukaryotes.

• Helminths: Parasitic worms.

• Viruses: Acellular infectious agents.

Additional info: These notes expand on the original bullet points with definitions, examples, and context for each major concept, suitable for introductory microbiology study.