Unit 3 Objectives Flashcards
Define Growth
An increase in population size via reproduction (Binary fission)
Is bacterial growth the same as human growth? Explain.
Bacterial growth is not the same as human growth;
Human growth involves physical enlargement and cellular differentiation, bacterial growth mainly refers to the reproduction and multiplication of cells.
Describe binary fission
A process where a single bacterial cell divides into two identical daughter cells. It begins with the replication of the bacterial chromosome, followed by the elongation of the cell. A septum then forms, splitting the cell into two, each with a copy of the original DNA
List the phases of microbial population growth. Describe what is happening at each phase. Draw & label a typical growth curve. When do you think would be the best time to use an antimicrobial drug? Explain.
Lag phase: the getting accustomed period; period of little or no cell division
Log (exponential phase): growth > death; metabolically active
Stationary phase: growth = death; metabolism slows
Death (decline) phase: growth < death; waste accumulates
The best time to use an antimicrobial drug is during the log (exponential) phase because the bacteria are actively dividing, making them more susceptible to the drug’s effects because of cell wall synthesis or DNA replication.
List ways to measure microbial growth. What are the advantages and disadvantages of each of these processes? (Without incubation)
Without incubation:
- Microscope counts: microscopic counting using a Petroff-Hausser counting chamber, where a sample is placed on a grid slide, and cells are counted to estimate the concentration in milliliters.
Advantage: this method is quick and useful for high cell concentrations
Disadvantage: has limitations, such as difficulty distinguishing between living and dead cells and counting rapidly moving microorganisms.
- Electronic counts: like the Coulter counter, count cells as they interrupt an electrical current in a narrow tube making it useful for larger cells such as yeasts and protozoa.
Advantage: its speed and ability to analyze many cells quickly
Disadvantage: its reduced effectiveness for bacterial counts due to debris and clumping in the sample
- Flow cytometry: a related technique that uses light-sensitive detectors to analyze cells
Advantage: allows scientists to distinguish and count different types of cells based on fluorescent dyes or antibodies.
List ways to measure microbial growth. What are the advantages and disadvantages of each of these processes? (With Incubation)
-
Serial Dilution and Viable Plate Counts
Serial dilution involves systematically diluting a liquid culture to reduce the number of cells to a manageable level for counting. Scientists then plate a set amount from each dilution onto agar surfaces and count the colonies that develop to estimate the original population size.
Advantage: ability to accurately estimate the number of viable bacteria
Disadvantage: it may underestimate the count if colony-forming units consist of multiple cells.
- Membrane Filtration: used to count microorganisms in low-density samples by filtering a large volume of liquid through a membrane that traps the cells. After filtering, the membrane is placed on a solid medium, where colonies can grow and be counted.
Advantage: its effectiveness for counting low-density populations,
Disadvantage: it may not capture all types of microorganisms due to variations in size and shape.
- Most Probable Number (MPN): a statistical approach to estimating bacterial populations based on dilution and growth in multiple test tubes. By inoculating sets of tubes with different dilutions and counting growth after incubation, researchers can reference MPN tables to estimate cell numbers.
Advantage: its usefulness for counting microorganisms that do not grow on solid media
Disadvantage: it requires multiple tubes and incubations, making it time-consuming.
- Turbidity: indirect method of estimating microbial population size by measuring the cloudiness of a broth culture, which increases as bacteria reproduce. A spectrophotometer is used to assess how much light passes through the culture, providing an estimate of the cell concentration.
Advantage: its speed and ease of use
Disadvantage: only works well for concentrations above 1 million cells per milliliter and does not differentiate between living and dead cells.
- Metabolic Activity: estimates cell numbers based on the rate of nutrient consumption and waste production by a population of microorganisms. By monitoring changes in nutrient levels or waste products, scientists can infer cell density in a culture.
Advantage: it provides real-time estimates of growth
Disadvantage: it may not directly correlate with cell numbers if metabolic rates vary widely among organisms.
- Dry Weight: involves filtering microorganisms from a culture, drying them, and weighing the biomass to estimate abundance. This method is particularly useful for filamentous organisms that are hard to count directly.
Advantage: provides a direct measurement of biomass
Disadvantage: it cannot track growth over time since the organisms are killed in the process.
Define photoautotroph
Organisms that use light energy to convert carbon dioxide (CO₂) into organic compounds, primarily through the process of photosynthesis. They generate their own food and are capable of producing oxygen as a byproduct
Energy: light (phototroph)
Carbon: CO2 (autotroph)
Define photoheterotroph
Organisms that obtain energy from light but rely on organic compounds for carbon sources, rather than fixing carbon dioxide. They use light to enhance their growth but cannot synthesize all necessary organic molecules from CO₂ alone.
Energy: light (phototroph)
Carbon: organic (heterotroph)
Define chemoautotroph
Organisms that derive energy from the oxidation of inorganic compounds (such as hydrogen sulfide or ammonia) and use this energy to fix carbon dioxide into organic compounds. They are often found in extreme environments where sunlight is not available.
Energy: chemical (chemotroph)
Carbon: CO2 (autotroph)
Define chemoheterotroph
Organisms that obtain both energy and carbon from organic compounds. They cannot synthesize their own food and must consume other organisms or organic matter for survival.
Energy: chemical (chemotroph)
Carbon: organic (heterotroph)
Define organotroph
Organisms that obtain electrons from organic substrates. They typically rely on organic compounds for energy and growth, often breaking them down through metabolic processes.
Electrons: organic (organotroph)
Define lithotroph
Organisms that obtain electrons from inorganic substances, such as minerals or metals. They can utilize these inorganic compounds in their metabolism to generate energy.
Electrons: inorganic (lithotroph)
How do environmental factors (oxygen levels) affect microbial growth & how can we use this information for practical application.
-Aerobic bacteria require oxygen for respiration
-Anaerobic bacteria grow in its absence
-Facultative anaerobes can thrive in both conditions.
-Application: Understanding oxygen requirements helps in the selection of appropriate growth media and conditions for culturing specific bacteria
How do environmental factors (osmotic pressure) affect microbial growth & how can we use this information for practical application.
-High osmotic pressure (hypertonic environments) can cause plasmolysis (shrinkage of the cell)
-Low osmotic pressure (hypotonic environments) can lead to lysis (bursting of the cell).
-Application: Food preservation techniques, like salting or sugaring, exploit osmotic pressure to inhibit microbial growth by creating hypertonic environments, effectively preserving food.
How do environmental factors (temperature) affect microbial growth & how can we use this information for practical application.
Each microbial species has an optimal growth temperature.
-Psychrophiles grow best in cold environments
-Mesophiles in moderate temperatures
-Thermophiles in hot conditions.
Extreme temperatures can denature enzymes and inhibit growth.
Application: Temperature control is vital in food storage, clinical settings, and industrial processes. For example, refrigeration slows down the growth of mesophilic bacteria in food, while pasteurization uses heat to kill pathogenic organisms.
How do environmental factors (pH) affect microbial growth & how can we use this information for practical application.
Microbes have an optimal pH range for growth. Most bacteria prefer a neutral pH (around 7), while some can thrive in
-Acidic (acidophiles)
-Alkaline (alkaliphiles) environments.
Application: The pH of growth media can be adjusted to favor specific microbial growth or inhibit unwanted microbes. For example, acidic conditions can be used to preserve foods, as many pathogens cannot survive in low pH.
How do environmental factors (salt concentrations) affect microbial growth & how can we use this information for practical application.
High salt concentrations can inhibit growth by creating osmotic stress. Some bacteria, known
-Halophiles, can thrive in high-salt environments, while others cannot tolerate it.
Application: Salting is a method used in food preservation. Additionally, understanding salt tolerance can help in biotechnological applications, such as the production of enzymes from halophilic organisms for use in high-salt conditions.
How do environmental factors (hydrostatic pressure) affect microbial growth & how can we use this information for practical application.
Increased hydrostatic pressure can affect microbial growth, particularly in deep-sea environments.
-Barophiles can thrive under high pressure, while many organisms cannot.
Application: Knowledge of hydrostatic pressure is essential for deep-sea microbial studies and bioprospecting for novel enzymes that function under extreme conditions.
