Lecture Notes - Applied Microbiology Overview

How did Carl Woese and Geoffrey Fox use rRNA to determine that Archaea were their own domain (and not genetically similar to bacteria)?

• Carl Woese and Geoffrey Fox utilized ribosomal RNA (rRNA) sequencing to establish that Archaea constitute their own distinct domain. By comparing the sequences of rRNA genes among different organisms, they demonstrated significant genetic divergence between Archaea and Bacteria, indicating that Archaea are not just simple variations of bacteria but a separate lineage altogether.

How do bacteria and Archaea increase genetic diversity?

• Bacteria and Archaea increase genetic diversity primarily through horizontal gene transfer (HGT), which allows them to exchange genetic material between different species. This mechanism includes transformation, transduction, and conjugation, which enhance adaptability and survival in various environments.

What is a Genus?

• A Genus is a taxonomic rank used in the biological classification of organisms, which groups species that are closely related and share a common ancestor. It is one level above species and is typically written with an initial capital letter (e.g., Canis for dogs and wolves).

What is a Species?

• A Species is defined as a group of organisms that can interbreed and produce fertile offspring under natural conditions. It represents the most specific level of classification in taxonomy, characterized by shared traits and genetic similarities.

What is a strain?

• A strain is a genetic variant or subtype of a microorganism, particularly within a species. Strains may exhibit different characteristics, such as virulence or resistance to antibiotics, reflecting their unique evolutionary paths.

What was Leeuwenhoek’s important contribution to microbiology?

• Leeuwenhoek’s crucial contribution to microbiology was the invention of the microscope and the first observation of microorganisms, which he called "animalcules". His detailed drawings and accounts of bacteria, protozoa, and other microscopic life paved the way for the field of microbiology.

What was the theory of spontaneous generation and how did Louis Pasteur “debunk” it?

• The theory of spontaneous generation posited that living organisms could arise from non-living matter. Louis Pasteur debunked this theory through his experiments with sterilized broths and flasks, demonstrating that microorganisms come from existing microbes in the air, not spontaneously from the broth itself.

What are Koch’s postulates and what do they tell us?

• Koch’s postulates are a set of principles used to establish a causative relationship between a microbe and a disease. They state that:

  • The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.

  • The microorganism must be isolated from a diseased organism and grown in pure culture.

  • The cultured microorganism should cause disease when introduced into a healthy organism.

  • The microorganism must be re-isolated from the experimentally infected organism.
    These postulates help in identifying pathogens responsible for diseases.

Describe light microscopy.

• Light microscopy utilizes visible light to illuminate specimens and glass lenses to magnify them. It allows the observation of live and fixed specimens, giving clear images at lower magnifications, but with limited resolution compared to electron microscopy.

Describe electron microscopy.

• Electron microscopy employs beams of electrons instead of light to view specimens, enabling much greater magnification and resolution. It can provide detailed images of cellular structures and organelles.

How does an electron microscope get better resolution?

• An electron microscope achieves better resolution by using electron beams which have shorter wavelengths than visible light, allowing finer details and structures to be resolved. Additionally, specialized techniques like oil immersion can enhance image clarity when observing specimens.