Chapter 1: The Microbial World and You – Study Notes

Chapter 1: The Microbial World and You

Introduction to Microbiology

Microbiology is the study of microorganisms, a diverse group of microscopic life forms that include bacteria, archaea, fungi, protozoa, algae, viruses, and some multicellular parasites. These organisms play essential roles in ecosystems, human health, and industry.

What is a Microbe?

Microbes are organisms that are typically too small to be seen with the unaided eye, though some exceptions exist. They can be unicellular, multicellular, or acellular, and include both prokaryotic and eukaryotic forms.

• Bacteria: Prokaryotic, single-celled organisms with peptidoglycan cell walls.

• Fungi: Eukaryotic organisms, including unicellular yeasts and multicellular molds and mushrooms.

• Protozoa: Eukaryotic, mostly unicellular organisms, often motile.

• Algae: Eukaryotic, photosynthetic organisms with cellulose cell walls.

• Viruses: Acellular entities with DNA or RNA, requiring a host cell for replication.

• Multicellular Animal Parasites: Eukaryotic, multicellular organisms such as helminths, with some microscopic stages.

Microbes in Our Lives

Microorganisms are vital to life on Earth. While a few are pathogenic, most are beneficial and perform essential functions:

• Decompose organic waste

• Generate oxygen via photosynthesis

• Produce chemicals (e.g., ethanol, acetone, vitamins)

• Ferment foods (e.g., cheese, bread, vinegar)

• Used in manufacturing and disease treatment (e.g., insulin)

• Prevent food spoilage and disease

The Microbiome

The microbiome refers to the community of microorganisms that inhabit a particular environment, such as the human body. Normal intestinal bacteria, for example, aid in digestion and protect against pathogens.

Naming and Classifying Microorganisms

Scientific nomenclature, established by Carolus Linnaeus, assigns each organism a two-part name: the genus (capitalized) and the specific epithet (lowercase), both italicized or underlined. For example, Escherichia coli.

Major Groups of Microorganisms

Bacteria

• Prokaryotic, single-celled

• Peptidoglycan cell walls

• Divide by binary fission

• Obtain nutrition from organic/inorganic chemicals or photosynthesis

• May be motile via flagella

Archaea

• Prokaryotic, lack peptidoglycan in cell walls

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

• Not known to cause human disease

Fungi

• Eukaryotic, chitin cell walls

• Absorb organic chemicals for energy

• Yeasts (unicellular), molds and mushrooms (multicellular)

• Molds form mycelia composed of hyphae

Protozoa

• Eukaryotic, unicellular

• Absorb or ingest organic chemicals

• Motile via pseudopods, cilia, or flagella

• Free-living or parasitic; some are photosynthetic

• Reproduce sexually or asexually

Algae

• Eukaryotic, cellulose cell walls

• Photosynthetic, produce oxygen and carbohydrates

• Found in freshwater, saltwater, and soil

• Reproduce sexually and asexually

Viruses

• Acellular, consist of DNA or RNA core

• Core surrounded by protein coat, sometimes with lipid envelope

• Replicate only inside living host cells

• Inert outside living hosts

Multicellular Animal Parasites

• Eukaryotic, multicellular animals

• Include helminths (flatworms and roundworms)

• Some life stages are microscopic

Classification of Microorganisms

Carl Woese developed the three-domain system based on cellular organization:

• Bacteria

• Archaea

• Eukarya (includes protists, fungi, plants, animals)

Historical Foundations of Microbiology

The First Observations

• 1665: Robert Hooke observed "cells" in cork, beginning cell theory.

• 1623–1673: Anton van Leeuwenhoek observed "animalcules" (microbes) with simple microscopes.

The Debate over Spontaneous Generation

Spontaneous generation was the hypothesis that life could arise from nonliving matter. This was challenged by the concept of biogenesis, which states that living cells arise only from preexisting cells.

• 1858: Rudolf Virchow proposed biogenesis.

Disproving Spontaneous Generation

Louis Pasteur's experiments with swan-necked flasks demonstrated that microorganisms do not arise spontaneously, but from other microbes in the environment.

The Germ Theory of Disease

The germ theory states that microorganisms are the cause of many diseases. Key contributors include:

• Agostino Bassi (1835): Fungus caused silkworm disease.

• Louis Pasteur (1865): Protozoan caused another silkworm disease.

• Ignaz Semmelweis (1840s): Advocated handwashing to prevent puerperal fever.

• Joseph Lister (1860s): Used phenol to prevent surgical infections.

• Robert Koch (1876): Developed Koch's postulates to link specific microbes to specific diseases.

Prevention and Treatment of Diseases

Vaccination

• 1796: Edward Jenner developed the first vaccine (cowpox for smallpox).

Chemotherapy and Antibiotics

• Chemotherapy: Treatment of disease with chemicals (synthetic drugs or antibiotics).

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

• 1928: Alexander Fleming discovered penicillin from Penicillium fungus.

• 1940s: Penicillin mass-produced for clinical use.

Branches of Microbiology

• Bacteriology: Study of bacteria

• Mycology: Study of fungi

• Parasitology: Study of protozoa and parasitic worms

• Immunology: Study of immunity

• Virology: Study of viruses

• Microbial genetics: Study of microbial inheritance

• Molecular biology: Study of DNA-directed protein synthesis

Modern Microbiology: Applications and Impact

Recycling Vital Elements

Microbial ecology studies the interactions between microbes and their environment. Microbes recycle elements such as carbon, nitrogen, sulfur, and phosphorus, making them available to plants and animals.

Bioremediation

Microbes degrade organic matter in sewage and detoxify pollutants like oil and mercury, contributing to environmental cleanup.

Biotechnology and Recombinant DNA Technology

• Biotechnology: Use of microbes for practical applications (e.g., food production, chemical synthesis).

• Recombinant DNA technology: Genetic engineering of microbes to produce proteins, vaccines, and enzymes.

Normal Microbiota and Biofilms

• Normal microbiota: Microbes that inhabit the human body, providing protection and nutrients.

• Biofilms: Microbial communities attached to surfaces, often resistant to antibiotics and causing persistent infections.

Emerging Infectious Diseases (EIDs)

Emerging infectious diseases are new or increasing in incidence. Examples include:

• Viral: Zika, MERS, SARS, COVID-19, H1N1, H5N1, Ebola, Marburg, HIV

• Bacterial: MRSA, Clostridium difficile

Summary Table: Major Groups of Microorganisms

Group	Cell Type	Cell Wall	Reproduction	Nutrition	Example
Bacteria	Prokaryotic	Peptidoglycan	Binary fission	Organic/inorganic/photosynthesis	Escherichia coli
Archaea	Prokaryotic	None or pseudomurein	Binary fission	Various	Methanogens
Fungi	Eukaryotic	Chitin	Spores/budding	Absorption	Yeast, mold
Protozoa	Eukaryotic	None	Sexual/asexual	Absorption/ingestion	Amoeba
Algae	Eukaryotic	Cellulose	Sexual/asexual	Photosynthesis	Volvox
Viruses	Acellular	None	Host cell machinery	Host cell	HIV, Zika
Helminths	Eukaryotic	None	Sexual	Ingestion/absorption	Tapeworm