Microbiology: Introduction, Roles, and Historical Foundations ~ Chp 1

Microbiology Introduction

A. Microbes: Characterization

Microbiology is the study of microscopic organisms, including bacteria, fungi, archaea, protozoa, algae, and viruses. These organisms are classified based on their cellular structure, mode of nutrition, and ecological roles.

• Bacteria: Prokaryotes with no nucleus, cell wall made of peptidoglycan, and no membrane enclosed organelles

• Fungi: Non-motile, absorb nutrients, cell wall made of chitin.

• Archaea: Prokaryotes with cell walls not made of peptidoglycan; molecular structures distinct from bacteria.

• Protozoa: Motile (at least in one developmental stage), ingest nutrients by absorption or phagocytosis, no cell wall. Examples: Amoeba, Paramecium.

• Algae: Photosynthetic, some motile, cell wall made of cellulose.

• Viruses: Non-cellular entities; not classified by cell structure. They lack cell membranes and ribosomes and are obligate intracellular parasites.

B. Multi-cellular Organisms

Some microbes are multicellular and can be classified as follows:

• Arthropods: Vectors of human disease (e.g., ticks, lice, fleas, flies, mosquitoes).

• Helminths: Parasitic worms, including:

  • Roundworms (e.g., pinworms)

  • Flatworms (e.g., tapeworms)

C. Taxonomy

Taxonomy is the science of classification. Microbes are classified into domains and kingdoms based on cellular organization.

• Domains: Eukarya (all have eukaryotic cells)

Kingdom	Cell Type	Nutrition	Cell Wall Composition
Animalia	Multi-cellular	Ingest nutrients	No cell wall
Plantae	Multi-cellular	Photosynthetic	Cell wall made of cellulose
Fungi	Multi-cellular (molds, mushrooms), unicellular (yeasts)	Absorptive	Cell wall made of chitin
Protista	Multi-cellular (slime molds, algae), unicellular	Varied	Cell wall made of cellulose (algae)

• Eubacteria (Bacteria): Prokaryotes, cell wall made of peptidoglycan.

• Viruses: Not placed in the taxonomy above; acellular.

D. Immunology

Immunology is the study of host defense mechanisms against foreign agents (pathogens).

• Antigen: Any substance that elicits an immune response.

• Antibody: Protein produced by the immune system to neutralize antigens.

E. Epidemiology

Epidemiology is the study of the transmission and spread of diseases within populations.

• Incidence: Number of new cases in a population over a period.

• Prevalence: Total number of cases at a given time.

Our Friend the Microbe

Microbes play essential roles in ecosystems, industry, and health. Most are harmless or beneficial.

A. Photosynthesis

• Microbes account for approximately 80% of planetary photosynthesis.

• They release oxygen ($O_2$) and form the basis of food chains.

B. Nitrogen, Sulfur, and Phosphorus Fixation

• Microbes convert atmospheric nitrogen ($N_2$), sulfur, and phosphorus into usable forms for other organisms.

• Example: Nitrogen fixation by Rhizobium bacteria in plant roots.

C. Decomposers

• Microbes break down dead organic matter, recycling nutrients for the next generation.

D. Normal Flora

• Microbes in the gut aid digestion, prevent infections, and provide nutrients.

• Industrial exploitation: Use of microbes in food production.

E. Food Production

• Microbes are used to produce bread, cheese, wine, beer, yogurt, and other foods.

F. Vitamins and Antibiotics

• Microbes synthesize vitamins and antibiotics essential for health and medicine.

G. Recombinant DNA Technology

• Microbes are engineered to produce human proteins (e.g., insulin, growth hormone, interferons, erythropoietin).

• Used in crop improvement and medical diagnostics.

H. Diagnostics

• Immunological and DNA-based tests for pregnancy, disease, and microbial identification.

I. DNA Fingerprinting

• Used in criminal investigations, taxonomy, and identification of microbes.

J. Bioremediation

• Microbes are used to clean up sewage, toxic waste, and other pollutants.

Our Enemy the Microbe

Some microbes are pathogenic and cause diseases in humans, animals, and plants.

A. Human Disease

• Example: The Black Death (1347-1351) killed one-third of Europe's population.

• Microbial diseases have shaped human history.

B. Destruction of Food

• Microbes can spoil food and damage crops and livestock.

History of Microbiology

The development of microbiology as a science involved key discoveries and experiments that disproved spontaneous generation and established the germ theory of disease.

Key Historical Events

• 1665: Robert Hooke improves the compound light microscope, first to describe the cell.

• 1673: Anton van Leeuwenhoek, first to describe major classes of bacteria.

• Spontaneous Generation: Discredited idea that living things arise from non-living material.

• Theory of Biogenesis: Living things arise from pre-existing living things.

• 1668: Francesco Redi's experiment with jars and meat disproved spontaneous generation.

• 1745: John Needham's chicken broth experiment (covered and heated) supported spontaneous generation.

• 1765: Lazzaro Spallanzani's experiment (boiled broth, sealed flasks) refuted Needham's results.

• 1861: Louis Pasteur's swan-necked flask experiment finally disproved spontaneous generation.

Major Contributors

• Robert Koch: Developed the germ theory of disease, importance of pure culture, Koch's postulates.

• Edward Jenner (1796): First to develop a vaccine (smallpox).

• Joseph Lister (1860): First to develop aseptic surgical technique.

Additional info: Koch's postulates are a set of criteria used to establish a causative relationship between a microbe and a disease. Pasteur's work laid the foundation for modern microbiology and immunology.