Introduction to Microbiology for Majors

Course Overview and Re Relevance

This course, Microbiology for Majors (BIO 3054), is a foundational requirement for biology, biomedical science, and medical laboratory science majors. It is also important for students pursuing pre-medical, pre-dental, pre-pharmacy, and pre-physician assistant tracks. The course covers essential topics in microbiology, including microbial diversity, cell structure, metabolism, microbial growth, and the impact of microorganisms on human society.

The Microbial World: The Microbial World and Its Importance

Definition and Scope of Microbiology

• Microbiology is the study of microscopic organisms, including bacteria, archaea, fungi, protozoa, and viruses.

• Microorganisms are life forms too small to be seen by the naked eye and are found in every environment that supports life.

• Microbes are highly diverse in form and function, with many being single-celled, while others form complex multicellular structures.

• Microbes live in communities and interact with their environment and other organisms.

Importance of Microbiology

• Microorganisms are the oldest form of life and constitute a major fraction of Earth's biomass.

• They play critical roles in infectious diseases, agriculture, food and water safety, soil health, animal health, and fuel production.

• Microbes have significant impacts on human society, including both beneficial and harmful effects.

Examples of Microbial Impact

• Pathogens: Microbes can cause diseases such as COVID-19, influenza, measles, and food poisoning.

• Environmental: Microbes are involved in nutrient cycling, bioremediation, and biofuel production.

• Applied Microbiology: Microbes are used in biotechnology, industrial microbiology, and food production.

Microbial Diversity and Classification

• Microbes are classified into three domains: Bacteria, Archaea, and Eukarya.

• Bacteria and Archaea are prokaryotes, while Eukarya includes plants, animals, fungi, and protists.

• Viruses are obligate parasites that require a host cell to replicate.

Structure and Function of Microbial Cells

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes (Bacteria and Archaea) lack a membrane-bound nucleus and organelles.

• Eukaryotes (plants, animals, fungi, algae, protozoa) have a nucleus and membrane-bound organelles.

• All cells have a cytoplasmic membrane, cytoplasm, ribosomes, and genetic material.

• Some cells have a cell wall, which provides structural support.

Cell Size and Morphology

• Prokaryotic cells range from 0.2 to 600+ µm in diameter; eukaryotic cells are typically 5 to 100 µm long.

• Cell shape varies: cocci (spherical), bacilli (rod-shaped), spirilla (spiral), spirochetes (flexible spiral), and more.

• Cell size affects metabolism, with smaller cells having a higher surface-to-volume ratio, which supports more efficient nutrient and waste exchange.

Cellular Activities

• Metabolism: Chemical transformation of nutrients

• Enzyme activity: Protein catalysts for metabolic reactions

• Genetic information flow: DNA → RNA → Protein

• Motility: Many cells can move by self-propulsion

• Differentiation: Some microbes form specialized cell types

• Communication: Cells can interact via chemical signals

• Evolution: Genetic changes are passed to offspring

Microbial Diversity and Evolution

Three Domains of Life

• Bacteria: Prokaryotes, usually undifferentiated single cells, with 80+ phylogenetic lineages

• Archaea: Prokaryotes, historically associated with extreme environments, with 12+ lineages

• Eukarya: Includes plants, animals, fungi, and protists, with great diversity in size, shape, and physiology

LUCA and Evolution

• LUCA: Last Universal Common Ancestor, from which all life descended

• Life on Earth began ~3.8–4.3 billion years ago

• Atmosphere was originally anoxic; oxygenic photosynthesis evolved later

Microorganisms and the Biosphere

Microbial Habitats

• Microbes inhabit a vast range of environments, including extreme ones (hot springs, glaciers, high salt, high acidity/alkalinity, high pressure)

• Microbial communities are found in soil, water, air, and within other organisms, including humans

• Microbes play key roles in nutrient cycling, decomposition, and other ecological processes

Impact of Microorganisms on Human Society

Microorganisms as Disease Agents

• Microbes can cause infectious diseases in humans, animals, and plants

• Examples include COVID-19, influenza, measles, MRSA, and food poisoning

• Microbes can also be beneficial, e.g. in the production of antibiotics, vaccines, and fermented foods

Microorganisms in Agriculture and Food Production

• Microbes are involved in nitrogen fixation, decomposition, and nutrient cycling in soils

• They are also important in the production of fermented foods (e.g., cheese, yogurt, sauerkraut, kimchi, pickles, beer)

• Microbial contamination can cause food spoilage and foodborne diseases

Microorganisms in Industry and Biotechnology

• Microbes are used in the production of biofuels (e.g., ethanol from corn), antibiotics, enzymes, and other valuable products

• They are also used in bioremediation to clean up pollutants

Microorganisms and Human Health

• Microbes are part of the normal human microbiome, where they help digest food and synthesize vitamins

• They can also cause diseases, but many are beneficial or harmless

Tables and Diagrams

Comparison of Prokaryotic and Eukaryotic Cells

Major Morphologies of Prokaryotic Cells

Key Equations

Surface Area and Volume of a Sphere (Cell Size)

• Surface Area:

• Volume:

• Surface-to-volume ratio:

Microbiology in the News

• Pandemics: COVID-19

• Epidemics: Influenza, flu

• Endemic: RSV

• Outbreaks: Measles

• Antibiotic resistance: MRSA, MDTB

• Food and water contamination: Listeria, Cyclospora

• Bioterrorism, vaccines, probiotics, cancer, animal infections, environmental microbiology

Review Questions

1. List the 4 types of “organisms” that are studied in microbiology and give an example of each.

2. Besides the pathogen, what are the other 2 categories that affect whether a pathogen may cause disease? Explain how they can affect how/if a pathogen can cause disease.

3. Name something in the news about microbiology.

4. What are other subfields in microbiology besides disease?

5. Looking ahead- what’s one way of studying bacteria?

Additional Academic Context

• Microbiology is a required course for many health and biology-related majors.

• Microbiology is not required for the new Ecology/Evolution major.

• Microbiology is a prerequisite for some advanced biology courses (e.g., path microbiology, immunology, virology).