Bacterial Metabolism and Oxygen Requirements Quiz

Bacterial Structure and Function

• Bacteria are prokaryotic organisms, meaning they lack a nuclear membrane, mitochondria, Golgi bodies, and endoplasmic reticulum.
• Bacterial cells range from 0.1μm to 5μm in length, making them invisible to the human eye without a microscope.
• The cell wall is the outermost component of all bacteria, except for Mycoplasma species.

Shapes of Bacteria

• Bacteria can have various shapes, including:
  • Coccus (spherical or round)
  • Spirillum (thick, rigid spiral)
  • Bacillus (rod-shaped)
  • Vibrio (comma-shaped)
  • Spirochete (thin, flexible spiral)
  • Cocobacillus (oval-shaped)

Cytoplasmic Structures

• The cytoplasm of a bacterial cell contains:
  • DNA chromosome
  • Ribosomes
  • Proteins
  • Metabolites
• Bacterial chromosomes are single, double-stranded circles, unlike eukaryotic chromosomes.
• Bacteria have 70S ribosomes, which are smaller than eukaryotic ribosomes.
• The cytoplasmic membrane has a lipid bilayer structure, but lacks steroids like cholesterol.

Cell Wall

• The cell wall is composed of peptidoglycan (murein) and provides shape and protection to the cell.
• There are two types of cell walls: Gram-positive and Gram-negative.
• Gram-positive bacteria have a thick, multilayered cell wall, while Gram-negative bacteria have a thinner layer of peptidoglycan and an outer membrane with lipopolysaccharide (LPS).

Gram Stain

• The Gram stain is a technique used to differentiate between Gram-positive and Gram-negative bacteria.
• The process involves:
  • Heat fixation
  • Crystal-violet dye (primary stain)
  • Gram's iodine (mordant)
  • Decolorization solution
  • Safranin (counterstain)

External Structures

• Some bacteria have external structures, including:
  • Capsules: loose polysaccharide or protein layers that protect bacteria from phagocytosis and promote adherence to surfaces.
  • Flagella: long, thin structures responsible for bacterial motility.
  • Fimbria (pili): hairlike structures composed of protein subunits, involved in adherence to surfaces.

Special Structures

• Some bacteria, such as Bacillus and Clostridium, can form spores, which are:
  • Dehydrated, multishelled structures that protect bacteria in "suspended animation"
  • Contain a complete copy of the chromosome, essential proteins, and ribosomes
  • Have an inner membrane, two peptidoglycan layers, and an outer keratin-like protein coat

Bacterial Metabolism

• Bacteria must obtain or synthesize amino acids, carbohydrates, and lipids for building blocks of the cell.
• Bacterial growth requires:
  • Energy source
  • Water
  • Essential elements (C, O, H, N, S, P)
  • Important ions (K, Na, Mg, Ca, Cl)
  • Components of enzymes (Fe, Zn, Mn, Mo, Se, Co, Cu, Ni)
• Oxygen requirements vary among bacteria, with some requiring oxygen, some tolerant of oxygen, and others anaerobic.

Bacterial Growth

• Bacteria grow in colonies, with each colony originating from a single mother cell.
• Colony characteristics include:
  • Color
  • Size
  • Shape
  • Smell
• Bacterial growth can be influenced by factors such as:
  • Species of bacterium
  • Chemical composition of the medium
  • Temperature
• A typical bacterial growth curve consists of four phases:
  • Lag phase
  • Log phase
  • Stationary phase
  • Death phase### Bacterial Structure
• Bacteria are prokaryotic organisms, meaning they have no nuclear membrane, mitochondria, Golgi bodies, or endoplasmic reticulum.
• Bacterial cells range from 0.1 μm to 5 μm in length and are not visible to the human eye without a microscope.
• The cell wall is the outermost component common to all bacteria, except for Mycoplasma species.

Shapes of Bacteria

• Coccus: spherical or round shape
• Spirillum: thick, rigid spiral shape
• Bacillus: rod-shaped
• Vibrio: comma-shaped
• Spirochete: thin, flexible spiral shape
• Cocobacillus: oval-shaped
• Diplococcus: division in one plane, coccus arranged in pairs
• Streptococcus: division in one plane, coccus arranged in chains
• Tetrad: division in two planes, coccus arranged in squares of 4
• Sarcina: division in three planes, regularly arranged in cubes of 8
• Staphylococcus: division in three planes, irregularly arranged in grape-like clusters

Cytoplasmic Structures

• The cytoplasm of a bacterial cell contains the DNA chromosome, ribosomes, proteins, and metabolites.
• Most bacterial chromosomes are a single, double-stranded circle that is not contained in a nucleus.
• Bacteria have 70S ribosomes.
• The cytoplasmic membrane has a lipid bilayer structure similar to eukaryotic membranes, but lacks steroids (e.g., cholesterol), except for Mycoplasma species.

Cell Wall

• Rigid peptidoglycan (murein) layers surround the cytoplasmic membranes of most bacteria, except for Mycoplasma species.
• The cell wall is responsible for the shape of the cell.
• It protects the cell from osmotic lysis and provides a barrier against certain toxic chemical and biologic agents.
• There are two types of cell walls in bacteria: Gram-positive and Gram-negative, distinguished by their reaction to the Gram stain.
• Gram stain is a technique used to differentiate between Gram-positive and Gram-negative bacteria based on their cell wall constituents.

Gram Stain

• Heat fixation: a thin layer of the biological sample is spread on a slide and passed through a flame to paste the sample.
• Crystal-violet dye (primary dye): cover the smear with crystal-violet dye for 1 minute, then gently rinse off the stain with water.
• Gram's iodine (mordant): cover the smear with Gram's iodine for 1 minute.

Cell Wall Components

• Gram-positive bacteria have a thick, multilayered cell wall consisting mainly of peptidoglycan, proteins, teichoic and lipoteichoic acids, and complex polysaccharides.
• Gram-negative bacteria have a thinner layer of peptidoglycan (10% of the cell wall) and an outer membrane containing lipopolysaccharide (LPS).

Bacterial Metabolism

• The minimum requirements for bacterial growth are:
  • Energy source
  • Water
  • Essential elements (C, O, H, N, S, P)
  • Important ions (K, Na, Mg, Ca, Cl)
  • Components of enzymes (Fe, Zn, Mn, Mo, Se, Co, Cu, Ni)
• Bacteria can be classified according to their oxygen requirements:
  • Obligate aerobes: require the presence of molecular oxygen for metabolism and growth
  • Microaerophiles: require 5% to 10% oxygen for optimal growth
  • Facultative anaerobes: can grow in either the presence or absence of oxygen
  • Obligate anaerobes: cannot grow in the presence of oxygen
• Bacteria multiply by binary fission, involving cell elongation, DNA replication, cell wall and plasma membrane constriction, cross-wall formation, and cell separation.

Media and Culture

• Media are artificially prepared mixtures of various nutrients in appropriate concentrations, prepared for the biochemical requirements of microbes.
• Culture: microbes that grow and multiply in or on a culture media.
• The growth rate of a bacterial culture depends on three factors:
  • Species of bacterium
  • Chemical composition of the medium
  • Temperature
• Bacteria exhibit four phases of growth in a typical growth curve:
  • Lag phase: adaptation to the new environment
  • Log phase: rapid growth and division
  • Stationary phase: growth halts due to depletion of metabolites or buildup of toxic substances
  • Death phase: population size decreases, and cells lose their ability to divide

Colony and Genetics

• A colony is a visible mass of microorganisms originating from a single mother cell, and is a clone of bacteria all genetically alike.
• Bacteria grow in colonies, each with distinguishing characteristics such as color, size, shape, and smell.
• Bacterial chromosomes are a single, double-stranded circle contained not in a nucleus.
• Bacteria may contain extrachromosomal genetic elements such as plasmids or bacteriophages.
• Genetic material can be transferred between different strains of bacteria, allowing for the exchange of genes and characteristics.### Bacterial Structure
• Bacteria are prokaryotic organisms, simple unicellular organisms with no nuclear membrane, mitochondria, Golgi bodies, or endoplasmic reticulum.
• Bacterial cells range from 0.1 μm to 5 μm in length, making them not visible to the human eye without a microscope.
• The cell wall is the outermost component common to all bacteria (except Mycoplasma species).

Shapes of Bacteria

• Coccus: spherical or round shape
• Spirillum: thick, rigid spiral shape
• Bacillus: rod-shaped
• Vibrio: comma-shaped
• Spirochete: thin, flexible spiral shape
• Cocobacillus: oval shape

Cytoplasmic Structures

• The cytoplasm of the bacterial cell contains the DNA chromosome, ribosomes, proteins, and metabolites.
• Most bacterial chromosomes are a single, double-stranded circle that is not contained in a nucleus.
• Bacteria have 70S ribosomes.
• The cytoplasmic membrane has a lipid bilayer structure similar to that of eukaryotic membranes, but contains no steroids (e.g., cholesterol); (except Mycoplasma species).

Cell Wall

• Rigid peptidoglycan (murein) layers surround the cytoplasmic membranes of most bacteria (except Mycoplasma species which have no peptidoglycan).
• The cell wall is responsible for the shape of the cell.
• It protects the cell from osmotic lysis and also provides a barrier against certain toxic chemicals and biologic agents.
• There are two types of cell wall in bacteria: Gram-positive and Gram-negative.

Gram Stain

• Heat fixation: a thin layer of the biological sample is spread on the slide and passed through a flame to paste the sample.
• Crystal-violet dye (primary dye): cover the smear with crystal-violet dye for 1 minute, then gently rinse off the stain with water.
• Gram's iodine (mordant): cover the smear with Gram's iodine for 1 minute, then gently rinse off the stain with water.
• Decolorization solution: run the acetone/alcohol decolorizer over the smear until the solution appears clear, then gently rinse with water.
• Safranin (counterstain): cover the smear with safranin for 30 seconds, then gently rinse the stain with water.

External Structures

• Some bacteria have surface features external to the cell wall, such as capsules, flagella, and pili.
• Capsules: loose polysaccharide or protein layers that can protect bacteria from phagocytosis by the immune system, act as a barrier to toxic hydrophobic molecules, and promote adherence to other bacteria or host tissue surfaces.
• Flagella: long, slender, thin hair-like appendages responsible for bacterial motility, allowing the cell to swim (chemotaxis) toward food and away from poisons.
• Flagella are attached to cells in different places, and their number and location are distinctive for each genus, making them useful for bacterial classification.
• Fimbria (pili): hair-like structures on the outside of bacteria, composed of protein subunits (pilin), which can be morphologically distinguished from flagella.

Special Structure: Spore

• Under poor environmental conditions, some bacteria can convert from a vegetative state to a dormant state, or spore.
• Some Gram-positive (but never Gram-negative) bacteria, such as Bacillus and Clostridium, are spore formers.
• The spore is a dehydrated multishelled structure that protects and allows the bacteria to exist in "suspended animation".
• The spore contains a complete copy of the chromosome, the bare minimum concentrations of essential proteins and ribosomes, and a high concentration of calcium bound to dipicolinic acid.

Bacterial Metabolism

• Bacteria must obtain or synthesize amino acids, carbohydrates, and lipids for building blocks of the cell.
• The minimum requirements for growth are:
  • Energy source
  • Water
  • Essential elements (C, O, H, N, S, P)
  • Important ions (K, Na, Mg, Ca, Cl)
  • Components of enzymes (Fe, Zn, Mn, Mo, Se, Co, Cu, Ni)
• Microorganisms can be classified according to their oxygen requirements:
  • Obligate aerobes require the presence of molecular oxygen for metabolism and growth.
  • Microaerophiles require 5% to 10% oxygen for optimal growth.
  • Facultative anaerobes grow in either the presence or absence of oxygen.
  • Obligate anaerobes cannot grow in the presence of oxygen.

Bacterial Growth

• Bacteria multiply by binary fission.
• The growth rate of a bacterial culture depends on three factors:
  • The species of bacterium
  • The chemical composition of the medium
  • The temperature
• Some species can double in 20 minutes (e.g., Escherichia coli), while others take almost 20 hours (e.g., Mycobacterium tuberculosis).
• A bacterial growth curve typically exhibits four phases:
  • Lag phase: adaptation to the new environment
  • Log phase: exponential growth
  • Stationary phase: growth slows due to depletion of nutrients or buildup of toxic substances
  • Death phase: population size decreases

Culture Media

• A colony is a visible mass of microorganisms all originating from a single mother cell, making it a clone of bacteria.
• Bacteria grow in colonies, and each colony has distinguishing characteristics such as color, size, shape, and smell.
• Culture media are artificially prepared mixtures of various nutrients in appropriate concentrations.
• There are four general categories of culture media:
  • Enriched nonselective media
  • Selective media
  • Differential media
  • Specialized media

Bacterial Genetics

• Bacterial chromosomes are a single, double-stranded circle that is not contained in a nucleus.
• Bacteria may also contain extrachromosomal genetic elements such as plasmids or bacteriophages.
• Genetic material can be transferred between different strains of bacteria through the exchange of DNA.
• This exchange can be advantageous for the recipient, especially if the exchanged DNA encodes antibiotic resistance.