Microbiology Chapter 1: The Microbial World

Chapter 1: The Microbial World and You

• The study of microorganisms, their diversity, and their roles in human life and health.
• Includes the vast array of microbes: bacteria, archaea, fungi (yeast and molds), protozoa, algae and viruses (non-cellular).
• Microbes are incredibly diverse, some causing disease, and others playing essential roles in the environment, food production, and human welfare.

Outline

• Microbes in our lives
• Naming and classifying microbes
• A brief history of microbiology
• Microbes and human welfare
• Microbes and human disease

Microbes in Our Lives

• Microbes are single-celled organisms, invisible to the naked eye, requiring a microscope to be seen.
• Microbes are diverse and perform many functions.
• Some microbes cause disease, but most do not.
• Environmental microbes play vital roles (e.g., food chain, nutrient cycling, photosynthesis)
• Commercially useful microbes (e.g., chemical production, vitamins, fermented foods)

The Microbiome

• The human body contains many bacterial cells alongside body cells.
• Human microbiota refers to the bacteria in our intestines which aid in digestion and synthesize vitamins.
• Microbiota contribute to human health by preventing pathogenic bacteria colonization.
• Our bodies become populated by microbes at birth.
• The microbiome includes the microbes that interact with the human body.

Nomenclature

• The system used today for naming organisms was developed by Carolus Linnaeus in 1735.
• Each organism is assigned two names, italicized (underlined when written).
• The first name is capitalized, and the second is not, with abbreviations possible.
• Names may describe the organism, honor a researcher, or identify the habitat (e.g., Staphylococcus aureus).

Types of Microorganisms: Bacteria

• Bacteria are single-celled, prokaryotic organisms that lack a membrane-bound organelle containing DNA.
• Common shapes are spherical, rod-shaped, and spiral.
• Cells are surrounded by a cell wall containing chains of sugars (glycans) linked by amino acids (peptides).
• They reproduce asexually by binary fission, dividing into two equal cells.

Types of Microorganisms: Archaea

• Archaea are single-celled, prokaryotic organisms.
• Their cell walls differ from those of bacteria and are found in extreme environments.
• Examples include methanogens (methane producers), halophiles (salt-loving), and thermophiles (heat-loving).
• They don't cause disease commonly.
• They reproduce asexually.

Types of Microorganisms: Fungi

• Fungi are eukaryotes (DNA within a nuclear membrane).
• They can be unicellular (e.g., yeast) or multicellular (e.g., molds).
• Cell walls are composed of a polysaccharide called chitin.
• Fungi form multicellular structures (mycelia) which are networks of hyphae.

Types of Microorganisms: Protists

• Eukaryotes that lack cell walls, can move through using pseudopods, flagella, or cilia, and can be free-living or parasitic. (e.g., Protozoa).

Types of Microorganisms: Algae

• Eukaryotes with cell walls composed of cellulose (a type of polysaccharide).
• Require sunlight, carbon dioxide, and water to produce oxygen and carbohydrates.

Types of Microorganisms: Viruses

• Viruses are acellular (lack cellular structure), requiring electron microscopes.
• They are very small and simple, with a nucleic acid genome (either DNA or RNA) enclosed by a protein coat.
• Some have an optional lipid membrane (envelope).
• Viruses do not possess cellular machinery and are strictly parasitic (requiring host cells for reproduction)

Classification of Microorganisms

• Prior to the discovery of microbes, organisms were classified as plants or animals.
• In 1978, Carl Woese developed a classification system (now used)grouping all cellular organisms into three domains (Bacteria, Archaea, Eukarya).
• Bacteria and archaea are prokaryotes (lacking membrane-bound organelles) eukaryotes have them.

A Brief History of Microbiology

• Prokaryotes appeared on Earth before more complex lifeforms.
• For a long time, microbes were the only lifeforms on Earth.
• Early humans didn't recognize microbes.
• Advancements in technology were required to discover microbes.

The First Observations

• Robert Hooke (1665) used a microscope to view cells, the smallest structural unit of life, starting the cell theory.
• Late 17th century: scientists observed microbial cells ("animalcules") in various environments (rainwater, feces, dental plaque).

The Debate Over Spontaneous Generation

• After discovering microbes, scientists debated whether they arose spontaneously from nonliving matter or from pre-existing living cells (biogenesis).

The Theory of Biogenesis

• Scientists (including Louis Pasteur) performed experiments to demonstrate that microbes do not spontaneously generate, but instead emerge from pre-existing cells.

The Germ Theory of Disease

• For centuries, the cause of diseases remained unknown.
• Robert Koch (1876) developed the germ theory of disease, proposing that microbes cause infectious diseases.
• Koch's postulates established a set of criteria for linking specific microbes to specific diseases.

Vaccination

• Edward Jenner (late 18th century) developed the first vaccine against smallpox.
• Vaccination is based on the principle of inducing immunity against diseases using substances like vaccines.
• In his time the germ theory was not well accepted.

A Fortunate Accident – Antibiotics

• Alexander Fleming's accidental discovery of penicillin in 1928 led to the development of antibiotics, which treat bacterial infections, but resistance is a growing problem

Antibiotics

• Antibiotics have saved many lives, but some bacteria have evolved resistance to them (antibiotic resistance).
• Antibiotics generally work by targeting components of bacterial cells

The Genomics Era

• Scientists can now study microbes by "reading" their DNA (genomes).
• Techniques allow studying microbes without requiring them to be cultured, providing insights into their capabilities.
• Genome information allows understanding evolutionary relationships between microbes.

Microbes and Human Welfare

• Most microbes don't cause disease.
• Many microbes contribute to essential processes like nutrient recycling, helping with pest control, food production, and industrial technologies.

Biogeochemical Cycling

• Microbes play a vital role in converting chemical elements (e.g., nitrogen, carbon, oxygen) into forms useable by other organisms (for example, nitrogen fixation).

Bioremediation

• Microorganisms can help cleanup spills that involve oil and chemicals

Pest Control

• Some microbes produce toxins that specifically harm insects (without harming plants or other animals).

Microbes and Human Disease

• Disease is a condition disrupting normal body function, often caused by pathogens (disease-causing microbes).
• Pathogens aren't diseases themselves, but may cause diseases.
• Some diseases are caused by genetic factors, environmental factors or a combination of both.
• The body has defenses against pathogens.
• Some pathogens cause short-term or long-term diseases.
• Pathogens do not have diseases as their main goal. Survival and reproduction are the major goals.