Microbes in Our Lives

Introduction to Microorganisms

Microorganisms, or microbes, are organisms too small to be seen with the unaided eye. They play essential roles in the environment, industry, and health.

• Microorganisms include bacteria, fungi, protozoa, microscopic algae, and viruses.

• Most microbes are beneficial, but some are pathogenic (disease-producing).

Roles of Microbes

• Decompose organic waste, recycling nutrients in ecosystems.

• Generate oxygen through photosynthesis (e.g., algae).

• Produce chemical products such as ethanol, acetone, and vitamins.

• Produce fermented foods (e.g., vinegar, cheese, bread).

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

Importance of Microbiology Knowledge

• Prevents food spoilage.

• Prevents disease.

• Helps understand causes and transmission of disease to prevent epidemics.

The Microbiome

Definition and Importance

The microbiome is the collection of microbes that live stably on or in the human body. An adult human has about 30 trillion body cells and harbors another 40 trillion bacterial cells.

• Helps maintain good health.

• Prevents growth of pathogenic microbes.

• May help train the immune system to discriminate threats.

Normal and Transient Microbiota

• Normal microbiota: Microorganisms acquired on or in a healthy human being, starting at birth.

• May colonize the body indefinitely or fleetingly (as transient microbiota).

• Colonization occurs only at body sites that provide suitable nutrients and environment.

Microbiome Research Initiatives

• Human Microbiome Project (2007): Determined the makeup of typical microbiota and their relationship to human diseases.

• National Microbiome Initiative (NMI) (2016): Explores the role of microbes in various ecosystems.

Naming and Classifying Microorganisms

Scientific Nomenclature

Carolus Linnaeus established the system of scientific nomenclature in 1735. Each organism has two names: the genus and the specific epithet.

• Scientific names are italicized or underlined.

• The genus is capitalized; the specific epithet is lowercase.

• Names are Latinized and used worldwide; may be descriptive or honor a scientist.

Examples:

• Escherichia coli: Honors Theodor Escherich; describes habitat (colon).

• Staphylococcus aureus: Describes clustered (staphylo-) spherical (coccus) cells and gold-colored (aureus) colonies.

• After first use, names may be abbreviated (e.g., E. coli).

Types of Microorganisms

• Bacteria: Prokaryotes, single-celled, peptidoglycan cell walls, divide by binary fission, may have flagella.

• Archaea: Prokaryotes, lack peptidoglycan, often live in extreme environments (methanogens, extreme halophiles, extreme thermophiles), generally not pathogenic.

• Fungi: Eukaryotes, chitin cell walls, absorb organic chemicals, yeasts (unicellular), molds/mushrooms (multicellular, composed of hyphae).

• Protozoa: Eukaryotes, absorb/ingest organic chemicals, motile (pseudopods, cilia, flagella), free-living or parasitic, some photosynthetic, reproduce sexually/asexually.

• Algae: Eukaryotes, cellulose cell walls, photosynthetic, found in water/soil, produce oxygen and carbohydrates, sexual/asexual reproduction.

• Viruses: Acellular, DNA or RNA core, protein coat (sometimes lipid envelope), replicate only in living host cells, inert outside hosts.

• Multicellular Animal Parasites: Eukaryotes, multicellular animals (helminths: flatworms, roundworms), some microscopic stages.

Classification of Microorganisms

• Developed by Carl Woese in 1978.

• Three domains based on cellular organization:

A Brief History of Microbiology

Key Observations and Theories

• 1665: Robert Hooke – Living things are composed of cells (cell theory).

• 1623–1673: Anton van Leeuwenhoek – First observations of microbes (“animalcules”).

Spontaneous Generation vs. Biogenesis

• Spontaneous generation: Life arises from nonliving matter (vital force).

• Biogenesis: Living cells arise only from preexisting living cells.

These experiments contributed to the debate between spontaneous generation and biogenesis.