Microbiology Lecture Test 1 Review - Chapter 1

The Evolution of Microorganisms and Microbiology

• Scientific Definition of Microbiology:

  • Microbiology is defined as the scientific study of microscopic organisms.

• Classification of Microscopic Entities:

  • Cellular Microbes: Include fungi, protists, bacteria, and archaea.
  • Acellular Particles: Include viruses, viroids, satellites, and prions.

• Ubiquity of Microbes:

  • Ubiquitous is defined as being present or found everywhere.
  • Microbes are ubiquitous across the biosphere.

• History of Taxonomy and the Three Domains of Life:

  • Carl Linnaeus is recognized as the Father of Taxonomy.
  • Carl Woese differentiated all living organisms into $3$ distinct Domains based on ribosomal $\text{RNA}$ comparison.
  • The $3$ Domains of Life are:
  • Bacteria
  • Archaea
  • Eukarya

• Structural Comparison of Prokaryotic vs. Eukaryotic Cells:

  • Prokaryotic cells are structurally simpler and smaller, lacking membrane-bound organelles and nuclei.
  • Eukaryotic cells are structurally more complex and possess membrane-bound organelles and a true nucleus.

• Characteristics of the Three Domains:

  • Domain Bacteria:
  • Single-celled prokaryotic organisms.
  • Possess cell walls containing peptidoglycan.
  • Ubiquitous in distribution.
  • Some members are human or animal pathogens capable of causing disease.
  • Domain Archaea:
  • Single-celled prokaryotic organisms.
  • Characterized by distinct $\text{rRNA}$, specialized proteins, and unique membrane lipids that differentiate them from bacteria.
  • Cell walls completely lack peptidoglycan.
  • Not known to be pathogenic.
  • Frequently inhabit extreme environmental conditions.
  • Domain Eukarya:
  • More complex cellular structure than prokaryotes, though usually single-celled.
  • Contain membrane-bound organelles and a defined cell nucleus.
  • Includes protozoa, algae, yeast, and molds.

• Universal Cellular Features:

  • All living cells share four fundamental structures in common:
  1. Plasma membrane
  2. Cytoplasm
  3. Ribosomes
  4. Nucleic acid

• Molecular Evolution and the Endosymbiotic Theory:

  • $\text{RNA}$ as the Primary Macromolecule:
  • $\text{RNA}$ is considered the first biological macromolecule and the evolutionary precursor to $\text{DNA}$.
  • Functionally codes for proteins and actively regulates gene expression.
  • Evolutionary Dynamics:
  • Microbial evolution occurs primarily through genetic mutation or the acquisition of new genetic material via horizontal gene transfer.
  • Endosymbiotic Theory:
  • Endosymbiosis is defined as an interaction between $2$ organisms in which $1$ organism lives inside of the other.
  • Eukaryotes evolved through endosymbiotic relationships.
  • Structural and genetic evidence supporting this includes mitochondria, chloroplasts, and hydrogenosomes.

• Historical Milestones and Key Contributors in Microbiology:

  • Janssens: Built the $1^{\text{st}}$ compound microscope with a magnification range of $3\times$ to $9\times$.
  • Robert Hooke: Recognized as the Father of Cell Biology; operated microscopes with $20\times$ to $50\times$ magnification.
  • Antony van Leeuwenhoek: Recognized as the Father of Microbiology; first to describe microscopic organisms using lenses reaching up to $500\times$ magnification; published his findings.
  • John Needham: Proposed and advocated for the theory of spontaneous generation.
  • Lazzaro Spallanzani: Demonstrated that hay in a sealed, boiled environment does not generate microbes, providing empirical evidence disproving spontaneous generation.
  • Louis Pasteur:
  • Conclusively disproved spontaneous generation using custom swan-necked flasks.
  • Demonstrated the biological nature of fermentation.
  • Developed the process of pasteurization.
  • Created attenuated vaccines for anthrax and rabies.
  • Joseph Lister: Observed a significant increase in patient survival rates when phenol ($\text{carbolic acid}$) was utilized as an antiseptic during surgery, indirectly establishing microbes as a primary cause of disease.
  • Robert Koch: Established Koch's Postulates, a set of experimental criteria used to prove that a specific organism causes a specific disease (including recognition of inherent limitations).
  • Charles Chamberland: Developed an advanced porcelain filtration system capable of trapping bacteria, which directly enabled the subsequent discovery of tobacco mosaic virus by Ivanovsky and Beijerinck.
  • Edward Jenner: Administered the $1^{\text{st}}$ true vaccination by using cowpox virus to confer immunity against smallpox.
  • Emil von Behring and Shibasaburo Kitasato: Discovered serum antibodies and developed antitoxin therapies.
  • Elie Metchnikoff: Discovered phagocytic immune cells.
  • Sergei Winogradsky: Discovered nitrogen fixation and pioneered environmental microbiology.
  • Martinus Beijerinck: Recognized as a co-founder of virology (virus discovery) and a pioneer in selective culture media development.

• Fields of Study in Microbiology:

  • Microbiology encompasses both Basic and Applied fields, including:
  • Medical Microbiology
  • Public Health Microbiology
  • Immunology
  • Microbial Ecology
  • Agricultural Microbiology
  • Food Microbiology
  • Industrial Microbiology
  • Microbial Physiology

Microscopy

• Fundamentals of Light Microscopy:

  • Lenses bend light rays to enlarge images, forming the physical basis of light microscopy.
  • Magnification: Defined as enlarging the apparent size of an object.
  • Refractive Index: Defined as a measure of how much light bends as it passes through a specific substance.

• Key Metrics of Optical Resolution:

  • Resolution: Defined as image clarity, specifically the ability to distinguish between $2$ closely spaced points as separate entities.
  • Numerical Aperture ($\text{NA}$): A physical property describing the light-gathering capacity of a lens.
  • Limit of Resolution Formula:     $D = \frac{2}{\text{NA}_{\text{obj}} + \text{NA}_{\text{condenser}}}$
  • Role of Immersion Oil: Immersion oil minimizes light refraction at high magnifications, thereby increasing the numerical aperture ($\text{NA}$) and improving resolution.

• Principles of Specimen Staining:

  • Microorganisms have a refractive index virtually identical to water, creating low contrast.
  • Staining provides necessary optical contrast required for microscopic visualization.

• Types of Light Microscopes:

  • Bright-Field Microscope: Standard light microscope producing a dark image against a bright background.
  • Dark-Field Microscope: Image is formed solely by reflected light, producing a bright image against a dark background.
  • Phase-Contrast Microscope: Converts differences in light phases into variations in intensity, causing the microbe to appear darker than the bright background.
  • Fluorescence Microscope:
  • Fluorescence Definition: The process wherein a substance absorbs light at a shorter wavelength (higher energy) and emits light at a longer wavelength (lower energy).
  • Fluorescent specimens are excited with a specific wavelength of light and emit light at a longer wavelength to generate high-contrast images.
  • Confocal Microscope: Uses a laser beam to illuminate a fluorescently labeled specimen point-by-point, utilizing computer technology to render $3\text{D}$ image reconstructions.

• Staining Methodologies and Principles:

  • Simple Staining:
  • Involves the application of $1$ single dye.
  • Used to determine the presence, general size, morphological shape, and structural arrangement of microbes, while aiding in sample preservation.
  • Heat-Fixing:
  • Kills the microbial specimens.
  • Causes the cells to adhere firmly to the glass slide.
  • Increases cellular susceptibility to stain uptake.
  • Chemical Dyes and Cellular Charge Interactions:
  • Bacterial cellular surfaces carry a net negative ($-$) charge.
  • Basic Dyes: Possess a net positive ($+$) charge, directly binding to and staining the microbial cell.
  • Acidic Dyes: Possess a net negative ($-$) charge, are repelled by the microbial surface, and stain the surrounding background.
  • Differential Staining:
  • Utilizes $2$ or more dyes to differentiate distinct organisms or specific cellular structures based on chemical properties.
  • Gram Staining: Divides the majority of bacteria into Gram-positive ($\text{G}+$) or Gram-negative ($\text{G}-$) based on cell wall composition:
    • Gram-positive ($\text{G}+$): Stains purple due to a thick peptidoglycan layer.
    • Gram-negative ($\text{G}-$): Stains red/pink due to a thinner peptidoglycan layer and outer membrane.
  • Acid-Fast Staining:
    • Primary diagnostic stain for Mycobacterium species because their rich mycolic acid content prevents standard Gram staining.
    • Acid-fast organisms stain red; non-acid-fast organisms stain blue.

• Metric Length Conversions:

  • Ability to execute conversions from the base meter down to the nanometer ($10^{-9}\,\text{m}$).

• Electron and Advanced Probe Microscopy:

  • Electron microscopes utilize the short wavelength of an electron beam for illumination, employing electromagnetic lenses and vacuum chambers to direct the beam.
  • Transmission Electron Microscope ($\text{TEM}$):
  • Ultra-thin slices of specimen are bombarded with an electron beam.
  • Computer processing aggregates views to construct detailed structural images.
  • Scanning Electron Microscope ($\text{SEM}$):
  • The surface of an intact specimen is scanned with electrons.
  • Computer analysis yields realistic $3\text{D}$ surface topographical images.
  • Scanning Probe Microscope: An electrical probe passes directly over an electrically conductive sample surface.
  • Atomic Force Microscope: The premier type of scanning probe microscope suitable for living specimens, capable of imaging individual atoms.

Bacterial Cell Structure

• Bacterial Morphology and Arrangement:

  • Cell Shapes:
  • Cocci (spherical)
  • Bacilli (rod-shaped)
  • Coccobacilli (intermediate short rod)
  • Spiral shapes: Spirilla (rigid spiral), Vibrios (comma-shaped curved rod), Spirochetes (flexible spiral)
  • Pleomorphic (variable or irregular shape)
  • Cell Arrangements:
  • Single cells
  • Diplococci (pairs)
  • Streptococci (chains)
  • Staphylococci (clusters)
  • Tetrads (groups of four)
  • Sarcina (cubical packets of eight)
  • Mycelium (network of filamentous branching hyphae)

• Surface-to-Volume Ratio Dynamics:

  • Small cells possess a high surface-to-volume ratio.
  • Efficient diffusion across the membrane in small cells yields higher relative nutrient transport rates compared to larger cells.

• Labeling and Anatomy of a Bacterial Cell:

  • Envelope
  • Slime layer or Capsule
  • Cell Wall
  • Plasma Membrane
  • Cytoplasm
  • Ribosomes
  • Nucleoid
  • Flagellum
  • Pili

• Plasma Membrane Structure and Transport Systems:

  • Plasma Membrane Structure: A semi-permeable, protein-spanned lipid bilayer barrier that selectively regulates transport between the intracellular and extracellular environments.
  • Nutritional Requirements:
  • Macronutrients: Required in large quantities; includes proteins, lipids, nucleic acids, and carbohydrates.
  • Micronutrients: Required in trace amounts; serve supportive and enzymatic roles.
  • Transport Mechanisms:
  • Passive Transport: Requires no cellular energy expenditure ($\text{ATP}$). Includes osmosis, simple diffusion, and facilitated diffusion; net movement is always from high concentration to lower concentration.
  • Active Transport: Driven by cellular energy in the form of $\text{ATP}$ expenditure or the proton-motive force (an electrical/electron gradient across a membrane). Utilizes carrier protein channels:
    • Uniporters: Transport a single molecule in one direction.
    • Symporters: Transport two different molecules simultaneously in the same direction.
    • Antiporters: Transport two different molecules in opposite directions.
    • Group Translocation: Energetically modifies traveling molecules as they are transported across the membrane.
  • Iron Uptake Regulation:
  • Host fevers induce iron storage within the liver, withholding free iron from invading pathogenic microbes that require it for metabolic activity.

• Structural Architecture of Cell Walls:

  • Gram-Positive ($\text{G}+$) Cell Wall:
  • Composed primarily of a thick layer of $\text{NAG}$ ($N\text{-acetylglucosamine}$) and $\text{NAM}$ ($N\text{-acetylmuramic acid}$) cross-linked peptidoglycan.
  • Contains embedded teichoic acids.
  • Gram-Negative ($\text{G}-$) Cell Wall:
  • Composed of a thin inner layer of peptidoglycan situated between $2$ periplasmic spaces.
  • Surrounded by an outer membrane composed of lipids, proteins, and lipopolysaccharides ($\text{LPS}$).
  • Completely lacks teichoic acid.

• Cellular Response to Osmotic Environments:

  • Isotonic: Solute concentration inside and outside the cell is equal; no net movement of water.
  • Hypotonic: Solute concentration outside the cell is lower than inside; water rushes into the cell.
  • Hypertonic: Solute concentration outside the cell is higher than inside; water exits the cell.
  • Lysis: Cell rupture or explosion resulting from osmotic pressure influx in a hypotonic environment.
  • Plasmolysis: Shrinking or shriveling of the cellular protoplasm away from the wall in a hypertonic environment.

• Wall-Deficient Microbial Forms:

  • Protoplast: A Gram-positive ($\text{G}+$) bacterial cell that has completely lost its cell wall.
  • Spheroplast: A Gram-negative ($\text{G}-$) bacterial cell that has lost its peptidoglycan layer but retains its outer membrane.
  • Mycoplasma: Bacteria that naturally lack a cell wall entirely; their plasma membrane is structurally reinforced to resist osmotic lysis.

• Extracellular Layers, Inclusions, and Internal Architecture:

  • Glycocalyx: Polysaccharide coating that aids in cell adhesion to surfaces.
  • Capsule: A highly organized, tightly attached glycocalyx layer.
  • Slime Layer: An unorganized, loosely attached glycocalyx layer.
  • Functions of Outer Layers: Provide protection against host immune cells (phagocytosis), detergents, viral infection, and desiccation; may also assist in motility.
  • $\text{S}$-Layers: Highly structured geometric patterns of protein subunits; commonly serve as the primary cell wall in archaea.
  • Cytoskeleton: Protein filaments that provide structural support, maintain cell shape, and assist in intracellular microcompartmentation.
  • Inclusions: Aggregates or groupings of organic or inorganic substances stored within the cytoplasm.
  • Gas Vacuoles: Aggregates of gas vesicles that provide buoyancy control in aquatic environments.
  • Ribosomes: Intracellular sites of protein synthesis; bacterial ribosomes are $70\text{S}$, consisting of smaller subunits than eukaryotic $80\text{S}$ ribosomes.
  • Nucleoid: Cytoplasmic region containing $1$ circular bacterial chromosome physically anchored to the plasma membrane; lacks a surrounding nuclear membrane.
  • Plasmids: Small, double-stranded, extrachromosomal $\text{DNA}$ molecules that replicate independently of the chromosome; often harbor genes providing selective survival advantages.
  • Episomes: Genetic elements or plasmids capable of integrating directly into the host bacterial chromosome.

• External Appendages and Motility Mechanisms:

  • Fimbriae: Short, fine, hair-like appendages utilized for surface attachment and biofilm formation.
  • Sex Pili: Specialized protein appendages required for bacterial conjugation (transfer of plasmid or chromosomal $\text{DNA}$ between cells).
  • Pili: Appendages that mediate twitching motility across solid surfaces.
  • Flagella: The longest surface appendages, specialized for swimming motility via a characteristically distinct run and tumble pattern.
  • Swarming: Coordinated, group movement of bacterial cells across a moist surface utilizing flagella and secreted surfactants.
  • Spirochete Motility: Cell movement driven by the undulation of axial filaments (endoflagella) within the periplasmic space, producing a corkscrew rotation that spins the entire cell.
  • Taxis: Directional movement toward an attractant (nutrient/favorable environment) or away from a repellant (toxin/unfavorable environment), mediated by photoreceptors and chemoreceptors.

• Endospore Formation and Physiology:

  • Endospores: Specialized, dormant structures produced by certain bacterial genera in response to adverse environmental conditions (extreme heat, starvation, desiccation).
  • Characteristics: Exceptionally resistant to environmental physical and chemical stresses; remain dormant until favorable conditions return.
  • Germination: Process by which an endospore converts back into an actively metabolizing vegetative cell when nutrients and conditions improve.
  • Sporulation is strictly a survival mechanism, not a reproductive process.

Archaeal Cell Structure

• Comparative Structural Differences Between Bacteria and Archaea:
  • Plasma Membrane Lipids: Archaea possess unique membrane lipids with ether linkages and branched isoprenoid chains, differing fundamentally from bacterial ester-linked fatty acid lipids.
  • Cell Wall Composition:
  • Peptidoglycan is exclusive to Bacteria; Archaea never contain true peptidoglycan.
  • Archaeal walls are predominantly composed of protein $\text{S}$-layers directly tethered to the underlying plasma membrane.
  • Glycocalyx and Slime Layers:
  • Bacteria commonly form protective capsules or slime layers for immune evasion and adhesion.
  • Slime layers are extremely rare in Archaea; when present, they function primarily in cell-to-cell communication.
  • Motility Appendages:
  • Bacterial swimming is propelled by flagella (singular: flagellum).
  • Archaeal swimming is propelled by structurally and compositionally distinct archaella (singular: archaellum).