The Microbial World and You – Chapter 1 Study Notes

The Microbial World and You

Introduction to Microbiology

Microbiology is the study of microorganisms, which are organisms too small to be seen with the unaided eye. These include bacteria, viruses, fungi, protozoa, algae, and some animal parasites. Microorganisms play essential roles in ecosystems, human health, and disease.

• Microorganisms (microbes): Living organisms that are usually microscopic in size.

• Some microbes, such as algae and animal parasites, can be seen without a microscope in certain stages.

• Microbes are found everywhere: in soil, water, air, and as part of the human body.

Roles of Microorganisms

Importance in Health and Environment

Microbes have both beneficial and harmful roles in nature and human society.

• Normal microbiota: Microbes that live stably on or in the human body, contributing to health by preventing the growth of pathogens and aiding the immune system.

• Humans are composed of approximately 30 trillion body cells and are colonized by an additional 40 trillion bacterial cells.

• Transient microbiota: Microbes that temporarily colonize the body.

• Microbes are essential for nutrient cycling, decomposition, and maintaining ecological balance.

Naming and Classifying Microorganisms

Scientific Nomenclature

The system of naming organisms was established by Carolus Linnaeus in 1735. Each organism has a two-part scientific name (binomial nomenclature):

• Genus: Always capitalized.

• Specific epithet (species): Lowercase.

• Both names are italicized (or underlined when handwritten). Example: Escherichia coli or E. coli.

• Names often describe characteristics or honor scientists. Example: Staphylococcus aureus (staphylo- = clustered, coccus = spherical, aureus = golden color).

Types of Microorganisms

Bacteria

• Prokaryotic ("pre-nucleus"): No true nucleus.

• Unicellular, with peptidoglycan cell walls.

• Reproduce by binary fission.

• Obtain energy from organic/inorganic chemicals or photosynthesis.

• Move using flagella.

Archaea

• Prokaryotic, lack peptidoglycan in cell walls.

• Often found in extreme environments (e.g., halophiles, thermophiles).

• Not known to cause disease in humans.

Fungi

• Eukaryotic (true nucleus surrounded by a nuclear membrane).

• Cell walls contain chitin.

• Obtain nutrients by absorbing organic material.

• Can be unicellular (yeasts) or multicellular (molds, mushrooms).

Protozoa

• Unicellular eukaryotes.

• Obtain nutrients by ingesting organic chemicals.

• May move using pseudopods, cilia, or flagella.

• Some are photosynthetic; can reproduce sexually or asexually.

Algae

• Eukaryotic, mostly unicellular or simple multicellular.

• Cell walls contain cellulose.

• Found in freshwater, saltwater, and soil.

• Photosynthetic, producing oxygen and carbohydrates.

• Reproduce sexually or asexually.

Viruses

• Acellular (not composed of cells).

• Consist of DNA or RNA core surrounded by a protein coat; sometimes enclosed in a lipid envelope.

• Can only reproduce inside living host cells (obligate intracellular parasites).

Multicellular Animal Parasites

• Not strictly microorganisms, but include parasitic worms (helminths) with microscopic stages in their life cycles.

Classification of Microorganisms

Three Domains of Life

Microorganisms are classified into three domains:

Domain	Characteristics	Examples
Bacteria	Prokaryotic, peptidoglycan cell walls	Escherichia coli
Archaea	Prokaryotic, no peptidoglycan, extreme environments	Halophiles, thermophiles
Eukarya	Eukaryotic, includes fungi, protozoa, algae, plants, animals	Fungi, Protozoa

Historical Perspectives in Microbiology

Early Observations and Cell Theory

• Hippocrates and Aristotle speculated about links between environment and disease.

• Robert Hooke (1665): Observed "cells" in cork, leading to cell theory (all living things are composed of cells).

• Antonie van Leeuwenhoek: First to observe microorganisms ("animalcules") using a microscope.

Spontaneous Generation vs. Biogenesis

• Spontaneous generation: Hypothesis that life arises from nonliving matter.

• Biogenesis: Hypothesis that living cells arise only from preexisting living cells.

Key Experiments:

• Francesco Redi (1668): Showed that maggots do not arise from decaying meat unless flies lay eggs on it.

• John Needham (1745) and Lazzaro Spallanzani: Debated whether microbes arise spontaneously in broth.

• Louis Pasteur: Disproved spontaneous generation with swan-neck flask experiments, showing that microbes come from the air.

The Golden Age of Microbiology

Major Discoveries and Advances

• Edward Jenner: Developed the first vaccine (smallpox) using cowpox virus; foundation of immunology.

• Ignaz Semmelweis: Advocated handwashing to prevent puerperal fever.

• Louis Pasteur: Discovered fermentation, pasteurization, and disproved spontaneous generation.

• Joseph Lister: Introduced aseptic surgery techniques.

• Robert Koch: Developed the germ theory of disease and Koch's postulates for linking microbes to specific diseases.

Koch's Postulates

1. The same pathogen must be present in every case of the disease.

2. The pathogen must be isolated from the diseased host and grown in pure culture.

3. The cultured pathogen must cause the disease when inoculated into a healthy, susceptible animal.

4. The pathogen must be re-isolated from the inoculated animal and shown to be the original organism.

Development of Chemotherapy and Antibiotics

• Paul Ehrlich: Developed the first synthetic drug (Salvarsan) to treat syphilis; concept of the "magic bullet".

• Alexander Fleming: Discovered the first antibiotic, penicillin, produced by the fungus Penicillium.

• Antibiotics: Chemicals produced by bacteria and fungi that inhibit or kill other microbes.

• Development of antimicrobial resistance is a major modern challenge.

Modern Microbiology and Biotechnology

Genomics and Molecular Biology

• Genomics: Study of an organism's entire genetic material.

• Recombinant DNA technology: Combining DNA from different sources to produce useful products (e.g., human hormones).

• Microbiome research: Study of microbial communities in various environments, including the human body.

Branches of Microbiology

Field	Focus
Bacteriology	Study of bacteria
Mycology	Study of fungi
Phycology	Study of algae
Protozoology	Study of protozoa
Parasitology	Study of parasites
Virology	Study of viruses
Immunology	Study of the immune system
Taxonomy	Science of naming and classifying organisms

Microorganisms and Human Welfare

Environmental and Industrial Roles

• Microbes recycle vital elements (carbon, oxygen, nitrogen, sulfur, phosphorus) for use by plants and animals.

• Waste treatment: Microbes degrade organic matter in sewage and remove pollutants (e.g., oil, mercury).

• Biological control: Some bacteria produce toxins fatal to insect pests but harmless to animals and crops.

Example: Bioremediation

• Use of microbes to clean up environmental pollutants, such as oil spills.

Additional info: Some inferred details and clarifications were added to ensure completeness and academic context, especially where the original notes were fragmented or unclear.