Overview
This lecture covers the history, classification, and importance of microbes, major contributors to microbiology, and the development of germ theory and scientific methods in disease investigation.
Origins and Importance of Microbes
- Prokaryotes have existed for over 3.5 billion years; eukaryotic microbes for at least 1.5 billion years.
- Microbes are the source of all life forms and exist wherever there is water.
- Microbes regulate Earth's atmosphere and are primary producers and decomposers in ecosystems.
- The human microbiota (microbes living on and in us) outnumber our own cells and play key roles in digestion and immunity.
Classification and Characteristics of Microbes
- Microbes include bacteria, archaea, eukaryotes (protozoa, algae, fungi, helminths), and viruses.
- Bacteria have simple chromosome structures and cell walls made of peptidoglycan.
- Prokaryotes (bacteria, archaea) are unicellular and lack nuclei; eukaryotes can be unicellular or multicellular and have nuclei.
- Archaea are not pathogenic and live in extreme environments.
- Viruses are non-living, obligate intracellular parasites, much smaller than bacteria.
Key Contributors in Microbiology
- Robert Hooke first described eukaryotic microbes (1665).
- Antoni van Leeuwenhoek first described bacteria (1676).
- Carl Woese established the three-domain phylogenetic tree based on rRNA sequencing.
- Francisco Redi and Louis Pasteur disproved spontaneous generation.
- Pasteur developed the germ theory of disease and pasteurization.
- Robert Koch established postulates for linking microbes to disease.
Naming and Classification Systems
- Microbes are classified by size and genetic sequence comparisons (DNA/RNA).
- The Woese-Fox System divides life into bacteria, archaea, and eukarya.
- Linnaean binomial nomenclature is used for naming bacteria (Genus species).
Germ Theory and Scientific Method
- The germ theory states diseases are caused by microorganisms, not "bad air" (miasma).
- Scientific method involves observation, hypothesis, experimentation, and theory development.
- Pasteur's swan-neck flask experiment disproved spontaneous generation.
- Koch's postulates determine if a microorganism causes a disease.
Key Terms & Definitions
- Microbiology — Study of organisms too small to see unaided.
- Microbiota — All microbes living on or inside the human body.
- Microbiome — Collection of all microbial genes in/on the body.
- Prokaryote — Unicellular organism lacking a nucleus (bacteria, archaea).
- Eukaryote — Organism with a nucleus, can be uni- or multicellular.
- Germ theory of disease — Microorganisms cause diseases.
- Spontaneous generation — Disproven belief that life arises from nonliving matter.
- Pasteurization — Heating food to kill pathogens without altering structure.
- Koch's postulates — Steps to link specific microbes to disease.
- Woese-Fox system — Classification into bacteria, archaea, eukarya by rRNA sequencing.
Action Items / Next Steps
- Review examples of microbes and their roles.
- Memorize Koch’s postulates and Pasteur’s contributions.
- Prepare for quiz on microbial classification and history.