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Questions and Answers
Which process involves the transfer of genetic material from a donor to a recipient cell by viruses called bacteriophages?
Which process involves the transfer of genetic material from a donor to a recipient cell by viruses called bacteriophages?
What is the process by which bacteria take up fragments of naked DNA and incorporate them into their genomes?
What is the process by which bacteria take up fragments of naked DNA and incorporate them into their genomes?
Which mechanism results in the one-way transfer of DNA from a donor cell to a recipient cell through the sex pilus?
Which mechanism results in the one-way transfer of DNA from a donor cell to a recipient cell through the sex pilus?
What is the term for mobile DNA segments that move within a genome, between plasmids, and between plasmids and the genome?
What is the term for mobile DNA segments that move within a genome, between plasmids, and between plasmids and the genome?
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What is the term for the process by which bacteria take up fragments of naked DNA and incorporate them into their genomes?
What is the term for the process by which bacteria take up fragments of naked DNA and incorporate them into their genomes?
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Transformation is the process by which bacteria take up fragments of RNA and incorporate them into their genomes.
Transformation is the process by which bacteria take up fragments of RNA and incorporate them into their genomes.
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Transduction involves the transfer of genetic information from a donor to a recipient cell by viruses of bacteria called bacteriophages.
Transduction involves the transfer of genetic information from a donor to a recipient cell by viruses of bacteria called bacteriophages.
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Conjugation results in two-way transfer of DNA between donor and recipient cells.
Conjugation results in two-way transfer of DNA between donor and recipient cells.
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Transposition involves the movement of non-mobile DNA segments within a genome.
Transposition involves the movement of non-mobile DNA segments within a genome.
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Transformation is the only mechanism for genetic material exchange between bacterial cells.
Transformation is the only mechanism for genetic material exchange between bacterial cells.
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What is the size range of bacterial cells?
What is the size range of bacterial cells?
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Which of the following bacterial shapes is characterized by a thin, flexible spiral shape?
Which of the following bacterial shapes is characterized by a thin, flexible spiral shape?
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Which type of bacteria has a thicker layer of peptidoglycan and includes proteins, teichoic and lipoteichoic acids, and complex polysaccharides in its cell wall?
Which type of bacteria has a thicker layer of peptidoglycan and includes proteins, teichoic and lipoteichoic acids, and complex polysaccharides in its cell wall?
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What is the function of the capsule in some bacteria?
What is the function of the capsule in some bacteria?
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Under what conditions do some Gram-positive bacteria convert from a vegetative state to a dormant state known as spore?
Under what conditions do some Gram-positive bacteria convert from a vegetative state to a dormant state known as spore?
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Which of the following is true about microorganisms classified as microaerophiles?
Which of the following is true about microorganisms classified as microaerophiles?
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What characterizes the log phase of a typical bacterial growth curve?
What characterizes the log phase of a typical bacterial growth curve?
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Which type of culture media has added inhibitors that discourage the growth of certain organisms without inhibiting the growth of the organism being sought?
Which type of culture media has added inhibitors that discourage the growth of certain organisms without inhibiting the growth of the organism being sought?
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What is a colony defined as in bacterial metabolism?
What is a colony defined as in bacterial metabolism?
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Which type of bacteria can grow in either the presence or absence of oxygen?
Which type of bacteria can grow in either the presence or absence of oxygen?
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What is the term for an artificially prepared mixture of nutrients used for the cultivation of bacteria in the laboratory?
What is the term for an artificially prepared mixture of nutrients used for the cultivation of bacteria in the laboratory?
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Which phase of bacterial growth is characterized by the culture running out of metabolites or a toxic substance building up, leading to the cessation of growth?
Which phase of bacterial growth is characterized by the culture running out of metabolites or a toxic substance building up, leading to the cessation of growth?
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What is the term for a visible mass of microorganisms originating from a single mother cell?
What is the term for a visible mass of microorganisms originating from a single mother cell?
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What is the term for an artificially prepared mixture of nutrients used for the cultivation of bacteria in the laboratory?
What is the term for an artificially prepared mixture of nutrients used for the cultivation of bacteria in the laboratory?
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What is the term for a visible mass of microorganisms originating from a single mother cell?
What is the term for a visible mass of microorganisms originating from a single mother cell?
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Obligate anaerobes can grow in the presence of oxygen.
Obligate anaerobes can grow in the presence of oxygen.
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The lag phase of a typical bacterial growth curve is characterized by the most rapid growth.
The lag phase of a typical bacterial growth curve is characterized by the most rapid growth.
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Differential media inhibits the growth of Gram-negative bacteria.
Differential media inhibits the growth of Gram-negative bacteria.
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Study Notes
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.
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Test your knowledge of bacterial metabolism and oxygen requirements with this quiz. Explore the essential elements and important ions necessary for bacterial growth, as well as the classification of microorganisms based on their oxygen requirements.
