Chapter 1: A Brief History of Microbiology – Study Notes

Chapter 1: A Brief History of Microbiology

What Does Life Really Look Like?

This section introduces the origins of microbiology and the discovery of microorganisms.

• Antonie van Leeuwenhoek (Dutch):

  • First to make and use microscopes for examining microorganisms.

  • Described and visualized tiny animals, fungi, algae, and single-celled organisms, which he called "animalcules."

  • By the end of the 19th century, these organisms were called microorganisms.

How Can Microbes Be Classified?

Early scientists developed systems to classify living organisms, including microbes.

• Carl Linnaeus (Swedish): Developed a taxonomic system for naming and grouping organisms.

• Leeuwenhoek's microorganisms were grouped into six categories:

  • Fungi

  • Protozoa

  • Algae

  • Bacteria

  • Archaea

  • Small animals

Fungi

Fungi are eukaryotic organisms that obtain food from other organisms and have cell walls.

• Eukaryotic (have membrane-bound nuclei)

• Obtain food from other organisms

• Possess cell walls

• Categories:

  • Molds: Multicellular; have hyphae; reproduce by sexual and asexual spores.

  • Yeasts: Unicellular; reproduce asexually by budding; some produce sexual spores.

Protozoa

Protozoa are single-celled eukaryotes with diverse structures and modes of locomotion.

• Similar to animals in nutrient needs and cellular structure

• Live freely in water; some live in animal hosts

• Mostly asexual reproduction; some sexual reproduction

• Most capable of locomotion by:

  • Pseudopodia: Cell extensions that flow in the direction of travel

  • Cilia: Numerous, short, hairlike protrusions that propel organisms

  • Flagella: Extensions of a cell that are fewer, longer, and more whip-like than cilia

Algae

Algae are photosynthetic organisms that can be unicellular or multicellular.

• Unicellular or multicellular

• Photosynthetic

• Simple reproductive structures

• Categorized based on pigmentation, storage products, and cell wall composition

Bacteria and Archaea

Bacteria and archaea are prokaryotic microorganisms with distinct characteristics.

• Unicellular and lack nuclei

• Much smaller than eukaryotes

• Found everywhere there is sufficient moisture; some in extreme environments

• Reproduce asexually

• Bacterial cell walls contain peptidoglycan; some lack cell walls

• Archaeal cell walls composed of polymers other than peptidoglycan

The Golden Age of Microbiology

This era was marked by the search for answers to fundamental questions about life and disease.

• Key questions:

  • Is spontaneous generation of microbial life possible?

  • What causes fermentation?

  • What causes disease?

  • How can we prevent infection and disease?

Spontaneous Generation

• Aristotle proposed that living things can arise from nonliving matter (spontaneous generation).

Redi's Experiments

• Showed that when decaying meat was kept isolated from flies, maggots never developed.

• Meat exposed to flies became infested, casting doubt on Aristotle's theory.

Needham's Experiments

• Supported spontaneous generation; boiled beef gravy and plant infusions still developed microbes.

Spallanzani's Experiments

• Concluded that microorganisms exist in air and can contaminate experiments.

• Critics argued sealed vials did not allow enough air for organisms to survive.

Pasteur's Experiments

• Used "swan-necked flasks" to show that no microbial growth occurred unless exposed to dust/microbes from the air.

What Causes Disease?

• Germ theory of disease: Diseases are caused by specific microbes (pathogens).

• Robert Koch identified causative agents of disease and established Koch's postulates.

Koch's Postulates

• Suspected causative agent must be found in every case of the disease and absent from healthy hosts.

• Agent must be isolated and grown outside the host.

• When introduced to a healthy host, the agent must cause the disease.

• Same agent must be reisolated from the diseased experimental host.

How Can We Prevent Infection and Disease?

• Handwashing and antiseptics (Semmelweis and Lister)

• Nursing and hygiene (Nightingale)

• Infection control and epidemiology (Snow)

• Vaccination and immunology (Jenner)

• Chemotherapy (Ehrlich's "magic bullet" and Domagk's discovery of sulfa drugs)

Microbial Genetics

Microbial genetics explores the molecular basis of heredity in microorganisms.

• Avery, MacLeod, and McCarty: Genes are contained in DNA.

• Beadle and Tatum: Genes' activity is related to protein function.

• Translation of genetic information into protein explained.

• Rates and mechanisms of genetic mutation investigated.

• Control of genetic expression by cells described.

Molecular Biology

Molecular biology studies cell function at the molecular level.

• Explanation of gene sequences and cellular processes.

• Understanding evolutionary relationships and taxonomy.

• Woese: Discovered significant differences in nucleic acid sequences among cells, leading to the classification of Bacteria, Archaea, and Eukaryotes.

Recombinant DNA Technology

Recombinant DNA technology involves manipulating genes for practical applications.

• Genes in microbes, plants, and animals manipulated for research and industry.

• Examples: Human blood-clotting factor by E. coli, gene therapy, and genetically modified crops.

What Roles Do Microorganisms Play in the Environment?

• Bioremediation: Use of microbes to detoxify polluted environments.

• Recycling of chemicals such as carbon, nitrogen, and sulfur.

How Do We Defend Against Disease?

• Serology: Study of blood serum and immune responses.

• Immunology: Study of the body's defense against pathogens.

• Chemotherapy: Use of chemicals to treat disease (e.g., penicillin, sulfa drugs).