Microbiology Lecture Notes

Gram Negative Bacteria

• True Statement: Gram-negative bacteria have porin proteins in their outer membrane.

• Explanation:

  • Gram-negative bacteria possess a thin peptidoglycan layer located between the plasma membrane and an outer membrane. This outer membrane contains lipopolysaccharide (LPS) and porin proteins, which facilitate the transport of molecules across the membrane.

  • Teichoic acids are present in Gram-positive bacteria, not Gram-negative.

Temperature and E. coli

• Lethal Temperature: 95°C is most likely to kill E. coli.

• Explanation:

  • E. coli can grow at 37°C, which is its optimal growth temperature, and even at room temperature (21°C), but 95°C is far above its maximum survival temperature.

  • Extremely low temperatures can inhibit growth but not necessarily kill the bacteria.

Chemoautotrophic Bacteria

• Energy and Carbon Source: Chemoautotrophic bacteria in hydrothermal vents use hydrogen sulfide for energy and carbon dioxide as a carbon source.

• Explanation:

  • Chemoautotrophs obtain energy by oxidizing inorganic compounds, such as hydrogen sulfide. They use this energy to fix carbon dioxide into organic molecules.

Phylogenetic Relationships

• Phylogenetically Related Pairs: Paramecium and domestic cat are most related phylogenetically.

• Explanation:

  • Paramecium is a eukaryotic organism, thus it shares a more recent common ancestor with macroscopic eukaryotes than it does with prokaryotic organisms like E. coli or methanogens.

Pathogenic Microorganisms

• Classification: A pathogenic microorganism would be classified as a mesophile.

• Explanation:

  • Mesophiles grow best in moderate temperatures, typically between 20°C and 45°C.

  • Pathogenic microorganisms that infect warm-blooded animals are usually mesophiles because they thrive at body temperature.

Prokaryotic Cell Structures

• Internal Structures: Mitochondria are NOT found internal to the prokaryotic cell wall.

• Explanation:

  • Mitochondria are membrane-bound organelles characteristic of eukaryotic cells, not prokaryotic cells.

  • Prokaryotic cells contain ribosomes, a chromosome, inclusion bodies, and can form endospores.

Bacterial Cell Shape and Arrangement

• Description: Rod-shaped bacteria arranged end-to-end in a chain are called streptobacillus.

• Explanation:

  • "Strepto-" refers to a chain-like arrangement.

  • "Bacillus" refers to a rod shape.

Bacterial Characteristics

• Bacterium Identification: A bacterium that is Gram-positive, exhibits a filamentous growth pattern, and is used in preparing antibiotics is Streptomyces.

• Explanation:

  • Streptomyces is a genus of Gram-positive bacteria known for producing many antibiotics.

  • They exhibit filamentous growth.

Cyanobacteria

• Cyanobacteria Characteristics: Cyanobacteria are phototrophs.

• Explanation:

  • Cyanobacteria are photosynthetic bacteria that use light as an energy source.

Bacterial Identification

• Bacterium Identification: A Gram-negative, non-photosynthetic, spiral-shaped bacterium with an axial filament is Treponema.

• Explanation:

  • Treponema is a genus of spirochetes that possess an axial filament for motility.

Gram-Positive Cells

• Gram-Positive Structure: Gram-positive cells have multiple layers of peptidoglycan that help retain the crystal violet dye.

• Explanation:

  • The thick peptidoglycan layer in Gram-positive bacteria traps the crystal violet dye during Gram staining.

Necessity of a Cell Wall

• Cell Wall Function: The cell wall protects the cell in a hypotonic environment, preventing it from bursting.

• Explanation:

  • In a hypotonic environment, water enters the cell, causing it to swell. The cell wall provides structural support to prevent lysis.

Organism's Respiration Preference

• Respiration Preference: Organisms that prefer using oxygen for respiration but can continue to grow in an anaerobic environment are called facultative anaerobes.

• Explanation:

  • Facultative anaerobes can grow with or without oxygen, but they prefer using oxygen when available.

Nitrogen Fixation

• Nitrogen Fixation: Nitrogen fixation involves the conversion of nitrogen gas to biologically usable products.

• Explanation:

  • During nitrogen fixation, atmospheric nitrogen (N2) is converted to ammonia (NH3), which can be used by plants and other organisms.

Phylogenetic Relationships

• Phylogenetically Related Pairs: Animal and amoeba are most related phylogenetically.

• Explanation:

  • Both animals and amoebas are eukaryotes.

Classification of E. coli

• E. coli Classification: E. coli would be classified as a mesophile.

• Explanation:

  • E. coli grows best at moderate temperatures and is commonly found in the intestines of warm-blooded animals.

Anaerobic Respiration

• Anaerobic Respiration: Anaerobic respiration requires an inorganic terminal electron acceptor, and only prokaryotes can do it.

• Explanation:

  • Anaerobic respiration uses a terminal electron acceptor other than oxygen, such as sulfate or nitrate.

  • This process is unique to prokaryotes.

Organism Growth at 100 Degrees C

• Organism Classification: An organism that prefers growth at 100°C would be classified under Domain Archaea.

• Explanation:

  • Archaea often include extremophiles, which thrive in extreme conditions like high temperatures.

Bacterial Structures

• Superficial Resemblance: Bacterial flagella most superficially resemble eukaryotic cilia.

• Explanation:

  • While they differ structurally and functionally, both flagella and cilia are used for movement.

Eukaryotic Organelle

• Non-Membrane Bound Organelle: Ribosomes are the only eukaryotic organelle that is not a membrane-bound compartment.

• Explanation:

  • Ribosomes are present in all cells and responsible for protein synthesis.

Cell Wall Composition

• Cell Wall Component: Peptidoglycan is found in both gram-positive and gram-negative cell walls.

• Explanation:

  • Peptidoglycan is a unique component of bacterial cell walls.

Chromosomes in Bacterial Cells

• Number of Chromosomes: A typical bacterial cell contains 1 chromosome.

Bacterial Shape and Arrangement

• Bacterial Cell Description: Bacteria that are spherical and arrange themselves in chains are called streptococci.

• Explanation:

  • "Strepto-" indicates a chain arrangement and "cocci" refers to spherical shape.

Photosynthetic Eukaryotic Microorganisms

• Photosynthetic Microorganisms: Photosynthetic eukaryotic microorganisms (and also plants) contain mitochondria is true.

• Explanation:

  • Mitochondria are responsible for aerobic respiration in eukaryotic cells.

Endoplasmic Reticulum

• Rough Endoplasmic Reticulum: Archeabacteria would NOT be expected to have ribosomes present on a rough endoplasmic reticulum.

• Explanation:

  • Archeabacteria are prokaryotic and lack a rough endoplasmic reticulum.

Cell Growth

• Cell Growth Rate: As a cell grows larger, the volume increases much more quickly than the surface area.

• Explanation:

  • Volume increases by the cube of the radius, while surface area increases by the square of the radius.

Peptidoglycan Cell Wall

• Peptidoglycan Cell Wall: Escherichia would be expected to have a peptidoglycan cell wall with an outer membrane.

• Explanation:

  • Escherichia is a Gram-negative bacterium.

Eukaryotic Cells

• Eukaryotic Cells: Chloroplasts are found in EUKARYOTIC CELLS ONLY.

• Explanation:

  • Chloroplasts are organelles responsible for photosynthesis in plants and eukaryotic microorganisms.

Gram Positive Cell Walls

• Gram Positive Cell Walls: Gram positive cell walls contain more peptidoglycan layers than Gram negative cell walls.

• Explanation:

  • The thick peptidoglycan layer is a defining characteristic of Gram-positive bacteria.

Sunlight as Energy Source

• Sunlight as Energy Source: By definition, a phototroph uses sunlight as its energy source.