BIOL120 - Introduction to Microbiology, Chemistry, and Prokaryotes

The Evolution of Scientific Inquiry and the Scientific Method

  • Historical Context: Early human civilizations (hunter-gatherers) initially sought to understand nature for survival, specifically for food and security. This evolved into animal domestication and agriculture.

  • Philosophical Transition: Early philosophers moved away from supernatural explanations, seeking natural causes for physical events.

  • The Scientific Method: Defined as a systematic process to study and understand natural phenomena. The steps include:

    • Asking questions.

    • Proposing a hypothesis.

    • Gathering information/data.

    • Evaluating results to support or disprove the hypothesis.

    • Communicating results to the scientific community.

Early Microscopy and the Discovery of Microorganisms

  • Optical Technology: Telescopes used lenses to magnify distant objects. Lenses can also magnify small, close objects, provided the lens is of high quality to ensure clarity and lack of distortion.

  • Antonie van Leeuwenhoek (1600s1600\text{s}):

    • Profession: A Dutch draper and clothing merchant.

    • Innovation: As a hobby, he created tiny, high-quality lenses affixed to metal devices, inventing one of the first effective microscopes.

    • Observations: He examined blood, pond water, and scrapings from teeth. He discovered an invisible world of "animalcules"—tiny, living, cell-shaped organisms.

    • Legacy: His published drawings launched the field of microbiology and sparked a controversy regarding the origins of life.

The Debate Over Spontaneous Generation

  • Theory of Spontaneous Generation: The belief that small organisms (like frogs, flies, or maggots) could arise spontaneously from non-living or rotting material under specific conditions.

  • Francesco Redi's Experiment: Proved that maggots did not spontaneously appear on meat if it was protected by a mesh barrier that prevented flies from landing on it.

  • Louis Pasteur's Experiment: Disproved the idea that air itself or a "vital force" caused microbes to appear in broth.

    • The Swan-Neck Flask: Pasteur used a flask with a long, curved neck. Air could pass through, but dust-containing microbes were trapped in the bend of the neck.

    • Result: The broth remained clear unless the flask was tilted to touch the dust or the neck was broken, proving microbes come from the air/dust, not spontaneous generation.

The Golden Age of Microbiology and Vaccination

  • The Golden Age: A period of intense investigation into how microbes interact with humans and animals, leading to modern medical treatments.

  • Smallpox and Immunity: It was historically noted that survivors of smallpox developed immunity and could not be infected twice.

  • Edward Jenner (17961796):

    • Variolation: An early practice of scraping smallpox lesion fluid into the skin of healthy people; while it often worked, it occasionally caused death.

    • The Cowpox Observation: Jenner noted that milkmaids frequently contracted cowpox (a milder disease) and subsequently never caught smallpox.

    • The Experiment: Jenner inoculated a boy (James Phipps) with cowpox. After recovery, he inoculated the boy with smallpox; the boy did not get sick. This was the first documented successful vaccine.

Development of Aseptic Techniques and Handwashing

  • Oliver Wendell Holmes: An American physician who advocated for the prevention of "childbed fever" (post-childbirth infection). He suggested physicians transferred diseases between patients and recommended burning the bedding of the deceased.

  • Ignaz Semmelweis: A physician at Vienna General Hospital who observed high mortality rates in maternity wards staffed by medical students compared to those staffed by midwives.

    • Conclusion: Medical students were performing autopsies on victims of childbed fever and then attending to healthy mothers without cleaning themselves.

    • Intervention: Instituted mandatory handwashing, leading to a significant drop in mortality.

  • Joseph Lister: A British physician known as the pioneer of antiseptic surgery.

    • Method: Inspired by Pasteur, he experimented with spraying carbolic acid directly onto wounds and saturating surgical sites.

    • Outcome: Drastically reduced infection rates and improved surgical survival.

Germ Theory and Koch’s Postulates

  • Louis Pasteur and Germ Theory: Through work on fermentation, Pasteur showed that microbes carry out chemical reactions. This led to the theory that microorganisms invade the body to cause disease.

  • Robert Koch: A contemporary of Pasteur who identified the causative agents of anthrax, tuberculosis, and cholera.

  • Koch's Postulates: A definitive four-step process still used to identify the organism responsible for a disease:

    1. The organism must be present in every case of the disease but absent in healthy individuals.

    2. The organism must be isolated from a diseased host and grown in a pure culture.

    3. The organism must cause the disease when inoculated into a healthy individual.

    4. (Added later) The same pathogen must be re-isolated from the newly diseased experimental host.

Endospores and Antibiotics

  • Ferdinand Cohn: A botanist who discovered bacterial endospores.

    • Endospores: Highly resistant, dormant structures formed by some bacteria (e.g., Bacillus anthracis) to survive heat and chemicals. They cannot be destroyed by simple boiling.

  • Alexander Fleming: A physician who served in WWI and sought ways to treat infected wounds.

    • Lysozyme: Discovered in tears and saliva; it inhibited bacteria but was not clinically practical.

    • Penicillin (19281928): An accidental discovery where mold contamination on an agar plate inhibited the growth of bacteria. The mold produced a substance called penicillin.

    • Mass Production: Triggered by WWII, penicillin was mass-produced to save soldiers, ushering in the antibiotic age.

Taxonomy and the Classification of Life

  • Timeline: Evidence of single-celled organisms exists in the fossil record dating back 44 billion years.

  • Cell Types:

    • Prokaryotic: Bacteria and Archaea (basic, smaller).

    • Eukaryotic: Fungi, protozoa, algae, and helminths (roughly 1010 times larger, complex, contains organelles).

    • Acellular: Viruses and prions.

  • Taxonomy: The science of naming and classifying organisms.

  • Carl von Linne (Linnaeus): Developed the hierarchical system:

    • Kingdom $\rightarrow$ Phylum $\rightarrow$ Class $\rightarrow$ Order $\rightarrow$ Family $\rightarrow$ Genus $\rightarrow$ Species.

  • Binomial Nomenclature: Organizations are identified by Genus and species (e.g., Homo sapiens, Escherichia coli, or Staphylococcus aureus).

    • Formatting Rules: Italics when typed, underlined when handwritten. The genus is capitalized, and the species is lowercase.

Chemical Foundations: Atoms, Bonds, and Macromolecules

  • Atomic Structure:

    • Protons: Positive (++), located in the nucleus.

    • Neutrons: Neutral charge, located in the nucleus.

    • Electrons: Negative (−-), found in orbits around the nucleus.

  • Ions: Atoms with a charge due to losing electrons (Positive Ion) or gaining electrons (Negative Ion).

  • Chemical Bonds:

    • Covalent: Atoms sharing electrons.

    • Ionic: Attraction between opposite charges.

    • Hydrogen: Attraction caused by partial ionic charges.

  • Carbohydrates (Saccharides):

    • Structures: 55-carbon or 66-carbon chains in rings.

    • Types: Monosaccharides (simple sugars), Disaccharides (e.g., lactose), Polysaccharides (e.g., starch, cellulose, glycogen).

    • Function: Metabolic reactions and structural components (e.g., ribose in ATP).

  • Lipids:

    • Triglycerides: 33 fatty acids attached to 11 glycerol. Can be saturated (single bonds) or unsaturated (double bonds/liquid).

    • Phospholipids: A polar, hydrophilic phosphate head and two non-polar, hydrophobic fatty acid tails. Forms cell membrane bilayers.

    • Steroids/Waxes: Includes cholesterol and protective bacterial waxes.

  • Proteins:

    • Built from 2020 different amino acids.

    • Structure hierarchy: Primary (sequence), Secondary (helices/sheets), Tertiary (3D3\text{D} shape), Quaternary (multiple subunits, e.g., Hemoglobin).

    • Denaturation: Breakdown of shape (and function) via heat, chemicals, or acids.

  • Nucleic Acids:

    • Nucleotides: Composed of a pentose sugar (deoxyribose in DNA; ribose in RNA), a phosphate, and a nitrogenous base.

    • DNA: Double helix, stores genetic info.

    • RNA: Single chain; types include mRNA, tRNA, and rRNA; primary role is protein synthesis.

  • Adenosine Triphosphate (ATP): A nucleotide used for energy storage. Energy is released when the bond for the third phosphate is broken (ATP→ADP+Energy\text{ATP} \rightarrow \text{ADP} + \text{Energy}).

Bacterial Anatomy and Morphology

  • Morphologies:

    • Cocci: Round.

    • Bacilli: Rod-shaped/Oval.

    • Vibrio: Curved rod.

    • Spirillum: Spiral/Corkscrew.

    • Spirochete: Spring-shaped.

    • Branching Filaments.

  • Arrangements: Cocci may form chains (Streptococci) or clusters (Staphylococci).

  • External Structures:

    • Flagella: Provide motility via chemotaxis (moving toward/away from signals in a zig-zag "random walk"). Arrangements: Monotrichous (one end), Amphitrichous (both ends), Lophotrichous (bunches), Peritrichous (all over).

    • Fimbriae: Bristles for surface attachment.

    • Pili: Long tubes used for conjugation (sharing genetic material).

    • Nanotubes: Transfer nutrients and assist in energy production.

    • S Layer/Glycocalyx: Protective layers. Glycocalyx can be a loose "slime layer" or a dense, organized "capsule."

  • Biofilms: Complex microenvironments formed when cells stick to surfaces (e.g., catheters, pipes) and each other, protected by a sugar substance.

The Cell Envelope and Internal Structures

  • Cytoplasmic Membrane: Phospholipid bilayer; performs energy metabolism and nutrient transport in bacteria.

  • Peptidoglycan: Unique to bacteria; a mesh-like sugar/protein network that prevents osmotic bursting.

  • Gram Staining:

    • Gram-Positive: Thick layer of peptidoglycan.

    • Gram-Negative: Thin layer of peptidoglycan plus an outer membrane containing Lipopolysaccharide (LPS). LPS acts as an endotoxin when released into the blood.

  • Internal Anatomy:

    • Nucleoid: Area containing the single circular DNA chromosome.

    • Plasmids: Small, independent circular DNA; often carry antibiotic resistance.

    • Ribosomes: Sites of protein synthesis; made of rRNA and protein.

    • Inclusion Bodies/Microcompartments: Storage for nutrients, enzymes, or gases.

    • Endospores: Dormant form (sporangium stage) that survives extreme heat up to 121 ∘C121\,^\circ\text{C}.

Bacterial Growth and Population Dynamics

  • Binary Fission: A process where one cell divides into two identical cells.

  • Exponential Growth: Patterns of doubling (1→2→4→8→16→...1 \rightarrow 2 \rightarrow 4 \rightarrow 8 \rightarrow 16 \rightarrow ...). It takes 2020 generations for one cell to become 11 million.

  • The Growth Curve (in enclosed systems):

    1. Lag Phase: No increase in number; cells prepare for division.

    2. Exponential (Log) Phase: Maximum rate of binary fission; population doubles continuously.

    3. Stationary Phase: Growth rate equals death rate as nutrients deplete and waste builds up.

    4. Death Phase: Population declines as cells die off.

Questions & Discussion

  • Question: What did Redi's experiment prove?

    • Answer: It proved that maggots arise from flies landing on meat, not from the meat itself (disproving spontaneous generation for large organisms).

  • Question: How did Pasteur's experiment differ from Redi's?

    • Answer: Pasteur used a swan-neck flask to show that even when air (the "vital force") was present, microbes did not grow unless they had physical access to dust/contaminants.

  • Knowledge Check 1: True or False: Humans have always known about microbes and how they cause disease.

    • Answer: False.

  • Knowledge Check 2: Who was a pioneer of aseptic surgical techniques?

    • Answer: Joseph Lister.

  • Knowledge Check 3: What is the process of determining the specific organism that causes disease?

    • Answer: Koch's Postulates.

  • Knowledge Check 4: True or False: Ions are atoms containing only neutrons that have no charge.

    • Answer: False (Ions have charge due to electron loss/gain).

  • Knowledge Check 5: Triglycerides are made up of glycerol and three ______?

    • Answer: Fatty acids.

  • Knowledge Check 6: Nucleotides contain: a pentose sugar, a phosphate, and a nitrogenous base. (All of these).

  • Knowledge Check 7: True or False: Bacterial endospores are the easiest cell structure to destroy by heat.

    • Answer: False (They are the hardest).

  • Knowledge Check 8: Which part of the growth curve shows the cells doubling in number?

    • Answer: Exponential growth phase.

  • Knowledge Check 9: If a cell has a generation time of 1010 minutes, how long would it take for that cell to increase in number to become 512512 cells?

    • Answer: 1.51.5 hours (9090 minutes). Explanation: 1→2→4→8→16→32→64→128→256→5121 \rightarrow 2 \rightarrow 4 \rightarrow 8 \rightarrow 16 \rightarrow 32 \rightarrow 64 \rightarrow 128 \rightarrow 256 \rightarrow 512 is 99 doublings. 9×10 minutes=90 minutes9 \times 10\,\text{minutes} = 90\,\text{minutes}.