Module 3 - Microbial Growth Flashcards
What are the four basic phases of bacterial growth?
- Lag phase
- Log phase
- Stationary phase
- Death phase
What occurs during the lag phase of bacterial growth?
Period of little to no cell division; cells do not immediately reproduce but undergo intense metabolic activity
What is another name for the log phase in bacterial growth?
Exponential growth phase
What characterizes the log phase of bacterial growth?
Cells divide actively, and generation time reaches a constant minimum
What happens during the stationary phase of bacterial growth?
Growth rate slows, number of deaths balances new cells, and population stabilizes
What defines the death phase in bacterial growth?
Number of deaths exceeds new cells, leading to a decline until the population diminishes or dies out
What is a batch culture?
Method of growing microorganisms in a closed system with nutrients provided only at the start
What is a continuous culture?
Also known as open system; continuously supplies nutrients and removes waste products
How do bacterial cells reproduce?
By binary fission, where one cell divides into two
What is the basic equation for exponential bacterial growth?
N = N₀ * 2^n
What does each symbol represent in the equation N = N₀ * 2^n?
- N: Final number of cells
- N₀: Initial number of cells
- n: Number of generations
How can generation time be calculated?
Using a semilogarithmic plot where the slope represents the growth rate (k)
What is the division rate (v) in microbial growth?
Reciprocal of the generation time; indicates how many generations occur per unit of time
What is the optimum temperature for most pathogenic bacteria?
37 degrees Celsius
What are psychrophiles?
Cold-loving microbes that grow within a temperature range of 0–20 degrees Celsius
What are mesophiles?
Moderate temperature-loving microbes that grow between 25 and 40 degrees Celsius
What are thermophiles?
Heat-loving microbes that can grow at temperatures between 55–80 degrees Celsius
What role do heat shock proteins (HSPs) play in stress response?
Assist microbes in handling heat stress by refolding damaged proteins
What are aerobic bacteria?
Bacteria that require oxygen for growth
What are obligate aerobes?
Bacteria that can grow only in the presence of oxygen
What are facultative aerobes?
Bacteria that can grow with or without oxygen; most pathogenic bacteria belong to this group
What are obligate anaerobes?
Bacteria that can grow only in the absence of oxygen
What is the pH range for most pathogenic bacteria?
Between pH 7.2 and 7.6
What is osmotic pressure in relation to microbial growth?
Factors such as osmotic pressure and salt concentration affect the growth of bacteria
What are osmophilic bacteria?
Organisms requiring high osmotic pressures
What happens to bacteria in a hypertonic solution?
Causes osmotic withdrawal of water, leading to plasmolysis
What are barophiles?
Microbes that have adapted to high pressures, such as those found at the ocean’s bottom
What is the effect of radiation on cells?
Causes damage to DNA, leading to mutations and cell destruction
How do bacterial endospores respond to ionizing radiation?
They are extremely resistant to the harmful effects
What types of radiation cause mutations and destruction of the cell’s DNA?
X-rays and gamma rays
These types of ionizing radiation can lead to significant cellular damage.
Which type of bacterial cells are extremely resistant to the harmful effects of ionizing radiation?
Bacterial endospores
Endospores can withstand extreme environmental conditions, including radiation.
What were vegetative cells thought to be in relation to ionizing radiation?
Quite susceptible
Vegetative cells are the active form of bacteria, as opposed to dormant endospores.
What is the purpose of DNA repair mechanisms in microorganisms?
To repair damage caused by radiation
These mechanisms help maintain cellular integrity and functionality.
Name one DNA repair mechanism used by microorganisms.
Photoreactivation
This mechanism involves the direct reversal of DNA damage caused by UV light.
What is another DNA repair mechanism besides photoreactivation?
Excision repair
This mechanism removes damaged DNA and replaces it with the correct sequence.
What is the SOS response in microorganisms?
A DNA repair mechanism activated in response to extensive DNA damage
This mechanism allows cells to repair DNA damage that might otherwise lead to cell death.
