microbiology exam 2 chapter 4 Flashcards
What factors determine the growth rates of microbes?
Microbial growth rates are determined by nutrition and niche-specific physical parameters like temperature and pH.
What is the growth rate range of microbes?
Microbes have both the fastest and the slowest growth rates of any known organisms, such as hot-spring bacteria (fast) versus deep-sea sediment microbes (slow).
How do most bacteria divide?
Most bacteria divide by binary fission, where one parent cell splits into two equal daughter cells.
Do all bacteria divide symmetrically?
No, some bacteria divide asymmetrically, producing daughter cells that are not identical in size or function.
What is the first step in binary fission?
In binary fission, the cell elongates and DNA is replicated.
What happens after DNA replication in binary fission?
he cell wall and plasma membrane begin to constrict as the cell prepares for division.
How are the two daughter cells formed in binary fission?
A cross-wall forms, completely separating the two DNA copies, and then the cells separate.
What is the growth rate in microbiology?
The growth rate refers to the rate of increase in cell numbers or biomass
How is the number of cells in binary fission related to the number of generations?
in binary fission, the number of cells is proportional to 2ⁿ, where n is the number of generations.
Why is microbial growth rate called exponential?
It is called exponential because cell numbers double within a specific time interval, leading to an exponential curve.
What is generation time in microbiology?
Generation time is the time it takes for a population to double in number.
how does generation time compare between bacteria and eukaryotes?
Generation time is shorter for most bacteria compared to eukaryotes.
What factors affect generation time?
Generation time depends on growth medium and incubation conditions.
What is the formula to calculate cell number during binary fission?
The formula is:
N = No x 2ⁿ
Where:
N = final cell number
No = original cell number
n = number of generations (during exponential growth).
What happens to exponential growth in a batch culture system?
Exponential growth never lasts indefinitely due to changing environmental conditions in a batch culture system.
What is a batch culture/closed system in microbiology?
A batch culture is a liquid medium in a closed system, where bacteria grow without the addition of fresh nutrients or removal of waste.
How do changing conditions in a batch culture affect bacterial growth?
The changing conditions in a batch culture significantly affect bacterial physiology and growth, showcasing bacteria’s ability to adapt to their environment.
simplest wat to model the effects of a changing environment is to culture bacteria in a
batch culture/closed system.
What is a key feature of a continuous culture?
In a continuous culture, all cells achieve a steady state, allowing detailed study of bacterial physiology.
What type of system is a continuous culture?
A continuous culture is an open system.
What is the role of the chemostat in a continuous culture?
The chemostat ensures logarithmic growth by continuously adding and removing equal amounts of culture media.
What natural system is similar to a chemostat?
The human gastrointestinal tract functions similarly to a chemostat.
What does the fresh medium in a continuous culture do?
The fresh medium is supplied from a reservoir to maintain nutrient levels.
What is the function of sterile air or other gas in a continuous culture?
Sterile air or gas provides oxygen and maintains proper gas exchange for microbial growth.
What does the flow-rate regulator control in a continuous culture system?
The flow-rate regulator controls the rate at which the medium enters and exits the culture vessel.
What is the role of the gaseous headspace in a continuous culture?
The gaseous headspace allows for gas exchange, providing oxygen and removing CO2.
What happens in the culture vessel of a continuous culture?
The culture vessel is where the microbial cells grow, maintained at steady conditions.
What is culture overflow in a continuous culture system?
Culture overflow is the excess effluent containing microbial cells that exits the system.
What does a chemostat illustrate about dilution rate, cell mass, and generation time?
A chemostat shows the complex relationships between dilution rate, cell mass, and generation time, where each factor influences microbial growth and physiology.
What is the method of direct counts for measuring microbial growth?
Direct counts involve counting all cells, living and dead, using a microscope or automated counter.
What is the method of viable counts?
Viable counts measure only living cells by counting colony-forming units (CFUs) on agar plates.
What does spectrophotometry measure in microbial growth?
Spectrophotometry measures the turbidity (cloudiness) of a culture, which is proportional to the cell density.
What does turbidity measurement in spectrophotometry indicate?
Turbidity measurement is an indirect, rapid, and useful method to measure microbial growth, often referred to as optical density (OD).
What must be established to relate a direct cell count to a turbidity value?
A standard curve must be established to relate a direct cell count to turbidity.
What are the advantages of using turbidity measurements for microbial growth?
Turbidity measurements are quick, easy to perform, and typically do not require destruction or significant disturbance of the sample.
What is a potential issue with turbidity measurements?
Turbidity measurements can be problematic if microbes form clumps or biofilms in the liquid medium.
What are the normal growth conditions for most organisms?
Normal growth conditions are:
Sea level
Temperature: 20°C–40°C
Neutral pH
0.9% salt
Ample nutrients
What are extremophiles?
Extremophiles are organisms that live in conditions outside the normal growth conditions.
What is the main criterion that determines the environment a species inhabits?
The main criterion is the tolerance of the organism’s proteins and other macromolecular structures to the physical conditions within that niche.
Can organisms face multiple extremes in their environment?
Yes, multiple extremes in the environment can be met simultaneously by organisms.
What environmental factors affect microbial growth?
The main environmental factors are:
Temperature
pH
Osmolarity
Oxygen
How does temperature affect microbial growth?
Microbial growth is influenced by temperature, with different species having optimal growth at specific temperatures.
How does pH affect microbial growth?
Microbial growth is sensitive to pH, with each species having an optimal pH range for growth.
What is the effect of osmolarity on microbial growth?
Osmolarity affects microbial growth by determining the water availability, with microbes adapted to specific osmotic conditions.
How does oxygen influence microbial growth?
Oxygen is essential for some microbes (aerobes) and toxic for others (anaerobes), with facultative anaerobes able to grow in both environments.
How does temperature affect a bacterial cell?
A bacterial cell’s temperature matches that of its immediate environment, and changes in temperature impact every aspect of microbial physiology.
What defines the growth limits of microorganisms in relation to temperature?
Each organism has an optimum temperature, as well as minimum and maximum temperatures that define its growth limits.
How do higher temperatures impact microbial growth?
Microbes that grow at higher temperatures can typically achieve higher rates of growth.
microbes can be classified by their
temperature
What are psychrophiles?
Psychrophiles are microorganisms that thrive at low temperatures.
What are mesophiles?
Mesophiles grow best at midrange temperatures, typically between 20°C and 45°C.
What are thermophiles?
Thermophiles are microorganisms that grow best at high temperatures, typically between 45°C and 80°C.
What are hyperthermophiles?
Hyperthermophiles thrive at very high temperatures, typically above 80°C.
How do organisms adapt to different temperatures?
Each group of microorganisms has membranes and proteins that are specifically suited to their growth temperature.
How do enzymes in psychrophiles adapt to cold environments?
Enzymes in psychrophiles function optimally at cold temperatures but are denatured or inactivated at higher temperatures.
What structural adaptations do enzymes in psychrophiles have?
Psychrophile enzymes have more α-helix and less β-sheet, more polar and fewer hydrophobic amino acids, and fewer weak bonds.
How does active transport occur in psychrophiles?
Active transport in psychrophiles is adapted to function at low temperatures.
What are the membrane adaptations in psychrophiles?
Psychrophiles have cytoplasmic membranes with higher content of unsaturated fatty acids to maintain a semi-fluid state at low temperatures.
What types of lipids are found in psychrophile membranes?
Some psychrophile membranes contain polyunsaturated fatty acids and long-chain hydrocarbons with multiple double bonds to maintain fluidity at low temperatures.
How do enzymes in thermophiles adapt to heat?
Enzymes in thermophiles are stable at high temperatures due to critical amino acid substitutions that help resist denaturation.
How do ionic bonds help thermophiles adapt to heat?
Thermophiles have an increased number of ionic bonds between basic and acidic amino acids, which help resist protein unfolding at high temperatures.
What is the role of hydrophobic interiors in thermophile proteins?
Thermophile proteins have densely packed, highly hydrophobic interiors that help stabilize them at high temperatures.
How do solutes contribute to thermophile stability?
Thermophiles produce solutes that help stabilize proteins and protect them from heat-induced damage.
How are the protein synthesizing machinery and cytoplasmic membranes adapted in thermophiles?
The protein synthesizing machinery and cytoplasmic membranes in thermophiles are heat stable, allowing them to function in high-temperature environments.
What is the role of saturated fatty acids in thermophile membranes?
Membranes in thermophiles are rich in saturated fatty acids, which form stronger bonds than unsaturated fatty acids, helping the membrane stay stable at high temperatures.
What triggers the heat-shock response in organisms?
Rapid temperature changes during growth activate stress response genes, triggering the heat-shock response.
What types of proteins are produced during the heat-shock response?
The heat-shock response produces chaperones to maintain protein shape and enzymes to modify membrane lipid composition.
Has the heat-shock response been observed in all organisms?
Yes, the heat-shock response has been documented in all living organisms examined so far.
danger zone for food preservation
50-20 degrees celsius
What happens at high temperatures for food preservation?
High temperatures destroy most microbes, although lower temperatures take more time for the process.
What happens during rapid growth temperatures for bacteria?
At rapid growth temperatures, bacteria grow quickly, and some may produce toxins.
What happens at refrigerator temperatures for bacteria?
Refrigerator temperatures slow bacterial growth; spoilage bacteria may grow slowly, but very few pathogens can grow.
What happens at freezing temperatures for bacteria?
At freezing temperatures, there is no significant growth of bacteria.
What is Thermus aquaticus?
Thermus aquaticus is a thermophilic bacterium that can survive in extremely high temperatures, often found in hot springs and thermal vents.
How does pH affect microbial growth?
The concentration of hydrogen ions (H+) or hydronium ions (H3O+) directly affects the cell’s macromolecular structures, and extreme pH values can limit growth.
why do extreme pH values limit microbial growth?
Extreme concentrations of hydronium (H3O+) or hydroxide ions (OH-) can disrupt cell processes and damage cellular structures, limiting growth.
How does microbial tolerance to pH compare to other chemical substances?
Microbial cells can tolerate a greater range of hydrogen ion (H+) concentration than almost any other chemical substance in the environment.
What are acidophiles?
Acidophiles are microorganisms that thrive in acidic environments, typically with a pH of 3 or lower (e.g., acidic soils, gastric fluids, or lemon juice).
What are alkaliphiles?
Alkaliphiles are microorganisms that thrive in alkaline environments, typically with a pH of 9 or higher (e.g., alkaline lakes, soap solutions, or household ammonia).
Which environments are suitable for acidophiles?
acidophiles can grow in volcanic soils, acid mine drainage, gastric fluids, lemon juice, and rhubarb, with pH values ranging from 1 to 5.
Which environments are suitable for alkaliphiles?
Alkaliphiles grow in environments like alkaline lakes, soda lakes, household ammonia, and lime solutions, with pH values ranging from 9 to 14.
At what pH level is neutrality in the pH scale?
Neutrality occurs at a pH of 7, where the concentrations of H+ and OH- ions are equal.
What are the optima, minima, and maxima in enzyme activity with regard to pH
Enzyme activity is affected by pH, and each enzyme has a pH optimum where it functions best, a minimum pH where the enzyme activity slows down, and a maximum pH where the enzyme activity stops.
How do bacteria regulate internal pH?
Bacteria actively regulate their internal pH to maintain a stable environment for enzymes and cellular functions, often using ion pumps or other mechanisms to prevent harmful changes in pH.
Why are weak acids used to preserve food?
Weak acids can pass through microbial cell membranes, disrupting the internal pH balance and killing the cells, making them useful in food preservation to prevent spoilage.
What role do buffers play in microbial culture media?
Buffers in microbial culture media help to maintain a constant pH, preventing harmful fluctuations that could affect microbial growth and enzyme activity.
What happens when weak acids enter microbial cells?
When weak acids pass through microbial membranes, they disrupt the internal pH balance, leading to cell damage or death by affecting pH homeostasis.
What pH range do Neutralophiles grow in?
neutralophiles grow in the pH range of 5–8 and include most pathogens. Most bacteria grow between pH 6.5 and 7, while molds and yeasts grow between pH 5 and 6.
What defines Acidophiles, and what is critical for their survival?
Acidophiles grow at pH less than 6. Some are obligate acidophiles. Their cytoplasmic membrane stability is critical for survival, as they must maintain their internal pH in acidic environments.
What defines Alkaliphiles, and how do they differ from other organisms?
Alkaliphiles grow at pH greater than 9. Some alkaliphiles use a sodium motive force instead of the typical proton motive force to maintain cellular functions in alkaline environments.
What is the pH range and salt concentration of saline soda lakes?
Saline soda lakes have high salt concentrations and pH values as high as pH 11.
What types of organisms are found in saline soda lakes?
Saline soda lakes contain alkalophiles such as:
The archaeon Halobacterium salinarum
The cyanobacterium Spirulina
What distinctive feature does Spirulina have in saline soda lakes?
Spirulina has high carotene concentrations, giving it a distinct pink color
What is the significance of Spirulina in the food chain?
spirulina is a major food source for the famous pink flamingo.
What does water activity (aw) measure?
Water activity (aw) measures how much water is available for use in a solution. It is defined as the ratio of the solution’s vapor pressure relative to that of pure water.
What is the required water activity level for most bacteria?
Most bacteria require water activity levels > 0.91 for growth.
What is the required water activity level for fungi?
Fungi can tolerate water activity levels > 0.86.
What is the typical water condition in microbial cells?
The cytoplasm of microbial cells typically has a higher solute concentration than the surrounding environment, causing water to move into the cell.
