Microbial Growth Factors
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Questions and Answers

What is the pH level at which most organisms grow optimally?

  • pH 7 (correct)
  • pH 9
  • pH 12
  • pH 4

What happens when temperatures exceed the maximum cardinal temperature for microbial growth?

  • Enzymes and nucleic acids become inactivated. (correct)
  • The microbe enters a dormant state.
  • Growth resumes at a higher rate.
  • Metabolism can continue indefinitely.

Which statement best describes the relationship between acid production and pH maintenance in microbial growth?

  • Acid production is beneficial for all microbes.
  • Maintenance of constant pH is crucial for organisms that produce acid to avoid self-poisoning. (correct)
  • Microbes can thrive in highly acidic environments without pH regulation.
  • Constant pH is only important for fungal species.

What are the cardinal temperatures for microbial growth?

<p>Minimum, Optimal, Maximum (C)</p> Signup and view all the answers

Which type of organism typically prefers a pH between 0 and 5.5?

<p>Acidophiles (D)</p> Signup and view all the answers

Which scenario describes the impact of low temperatures on microbial growth?

<p>Microbial activities are inhibited below the minimum temperature. (C)</p> Signup and view all the answers

What characterizes the optimal temperature for microbial growth?

<p>It maximizes growth and metabolism for a short period. (D)</p> Signup and view all the answers

Which group of organisms typically prefers a neutral pH for growth?

<p>Neutrophiles (B)</p> Signup and view all the answers

What is the primary role of DNA repair mechanisms in microbial growth?

<p>To allow recovery from moderate radiation damage (B)</p> Signup and view all the answers

Which statement best describes the role of Deinococcus radiodurans in relation to DNA?

<p>It has potent mechanisms to repair DNA damage. (D)</p> Signup and view all the answers

What initiates the stationary growth phase in microbial populations?

<p>The depletion of essential nutrients or accumulation of toxic products (C)</p> Signup and view all the answers

Which type of radiation is specifically known to cause the formation of thymine dimers in DNA?

<p>Ultraviolet radiation (C)</p> Signup and view all the answers

How does microbial growth differ from the growth of individual cells?

<p>Microbial growth focuses on population increases rather than individual alterations. (B)</p> Signup and view all the answers

What does the lag phase indicate about microbial growth after inoculation?

<p>Organisms are synthesizing necessary enzymes to adapt to a new medium. (C)</p> Signup and view all the answers

What is a characteristic of coenocytic microorganisms during growth?

<p>They undergo nuclear division without accompanying cell division. (C)</p> Signup and view all the answers

What is the consequence of mutations caused by ultraviolet radiation in microbial cells?

<p>Inhibition of cell replication and potential cell death (C)</p> Signup and view all the answers

What is the primary method through which most bacteria reproduce?

<p>Binary fission (C)</p> Signup and view all the answers

Which two pathways function during the bacterial cell cycle?

<p>DNA replication and partition (C)</p> Signup and view all the answers

Extreme halophiles require NaCl concentrations of what range to thrive?

<p>2M to 6.2M (D)</p> Signup and view all the answers

How do extremophiles differ from other organisms regarding environmental conditions?

<p>They thrive in conditions that are detrimental to most other life forms. (B)</p> Signup and view all the answers

What effect does pH have on microbial growth?

<p>The concentration of hydrogen ions can disrupt enzyme function. (A)</p> Signup and view all the answers

Which of the following is NOT a reproductive strategy observed in bacteria?

<p>Sexual reproduction (D)</p> Signup and view all the answers

What is a characteristic of halophiles compared to extreme halophiles?

<p>Halophiles grow optimally at concentrations above 0.2M. (A)</p> Signup and view all the answers

Which factor could most directly disrupt microbial enzyme function?

<p>Extreme pH levels (C)</p> Signup and view all the answers

What is the role of cytokinesis in the bacterial cell cycle?

<p>Divide the cytoplasm into two cells (C)</p> Signup and view all the answers

Which of these best describes microbial growth under harsh environmental conditions?

<p>Extremophiles thrive in conditions that would inhibit most organisms. (C)</p> Signup and view all the answers

What best describes the process of programmed cell death in a population of organisms?

<p>A fraction of the population has genes that trigger cell death. (C)</p> Signup and view all the answers

Which of the following best defines viable but non-culturable (VBNC) bacteria?

<p>Metabolically inactive bacteria that cannot divide but can be resuscitated. (B)</p> Signup and view all the answers

What is a defining characteristic of fed-batch culture compared to conventional batch culture?

<p>Nutrients are continuously supplied to prevent depletion. (C)</p> Signup and view all the answers

What is a key characteristic of continuous culture systems?

<p>Nutrients are continuously provided while waste is continually removed. (A)</p> Signup and view all the answers

Which of the following elements is NOT controlled in a chemostat during continuous culture?

<p>Nutrient absorption rate of microorganisms (A)</p> Signup and view all the answers

What advantage does fed-batch culture offer during biotechnological processes?

<p>Controlled feeding of nutrients while retaining products in the bioreactor. (B)</p> Signup and view all the answers

What are primary metabolites usually associated with in microorganisms?

<p>Normal growth and functioning of cells. (B)</p> Signup and view all the answers

What is the primary purpose of maintaining cells in log phase in continuous culture systems?

<p>To minimize the production of by-products that inhibit growth. (D)</p> Signup and view all the answers

In the context of continuous culture, what is meant by the term 'exponential phase'?

<p>A phase in which cell division occurs at a constant rate. (C)</p> Signup and view all the answers

Which of the following best describes secondary metabolites?

<p>Often serve as pharmaceuticals and biopesticides. (D)</p> Signup and view all the answers

Which apparatus maintains optimal growth conditions for microorganisms in large-scale fermentation?

<p>Fermentor (C)</p> Signup and view all the answers

Which factor is crucial for the successful operation of continuous culture systems?

<p>Balancing nutrient supply with growth and waste removal. (D)</p> Signup and view all the answers

What is a major consequence of failing to adequately maintain nutrient levels in a continuous culture?

<p>Inhibition of growth and potential cell death. (D)</p> Signup and view all the answers

How does fed-batch culture influence the yield of desired metabolites?

<p>By controlling concentrations of limiting nutrients. (B)</p> Signup and view all the answers

What can the control of pH in a chemostat primarily affect?

<p>Growth rate of microorganisms (B)</p> Signup and view all the answers

Which metabolic products are associated with the synthesis of microbial cells?

<p>Primary metabolites (C)</p> Signup and view all the answers

What is the optimal pH range for alkaliphiles to grow?

<p>pH 8.5 to pH 11.5 (D)</p> Signup and view all the answers

At what temperature is the lethality threshold for most microorganisms typically defined?

<p>70 °C for 10 minutes (A)</p> Signup and view all the answers

Microorganisms classified as thermoduric are mainly characterized by what trait?

<p>Ability to survive high temperatures (A)</p> Signup and view all the answers

Which adaptation helps stabilize the DNA of thermophiles?

<p>Increased histone-like proteins (A)</p> Signup and view all the answers

Which of the following is NOT a protective enzyme produced by aerobes?

<p>Aldose reductase (B)</p> Signup and view all the answers

Barophilic organisms are distinguished by which characteristic?

<p>They require or grow more rapidly under increased hydrostatic pressure (B)</p> Signup and view all the answers

What effect does ionizing radiation have on microorganisms?

<p>Causes mutations leading to death (B)</p> Signup and view all the answers

Strict anaerobic microorganisms typically lack which protective enzymes?

<p>Both A and B (C)</p> Signup and view all the answers

Psychrophiles are characterized by their optimal growth temperature range of?

<p>0 to 20 °C (B)</p> Signup and view all the answers

What defines the cardinal temperature range for mesophiles?

<p>20 °C to 45 °C (D)</p> Signup and view all the answers

Which of the following compounds can thermoresistance in microorganisms depend upon?

<p>Genetic properties and physiologic status (C)</p> Signup and view all the answers

What characteristic distinguishes barotolerant organisms from nontolerant organisms?

<p>They are adversely affected by increased pressure, but not as severely (D)</p> Signup and view all the answers

Which environmental condition is commonly associated with oligotrophic environments?

<p>Low nutrient concentrations (C)</p> Signup and view all the answers

Flashcards

Binary Fission

The process by which bacterial cells divide into two identical daughter cells. It involves DNA replication, partitioning, and cytokinesis.

Environmental Factors

A range of environmental conditions, such as temperature, pH, and salt concentration, that a microbe can tolerate for growth.

Extremophiles

Organisms that thrive in extreme conditions that would kill most other organisms, such as high temperatures, high salinity, or low pH.

Halophiles

Microbes that require high salt concentrations (above 0.2 M) for optimal growth.

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Extreme Halophiles

Halophiles that require very high salt concentrations (2 M to 6.2 M) for growth.

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Cytokinesis

The process by which cells divide their cytoplasm and organelles to create two daughter cells.

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Temperature Range

The range of temperatures at which an organism can grow.

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pH

The amount of hydrogen ions (H+) in a solution, expressed as a pH value.

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Bacterial Reproduction

A process in which bacteria replicate their genome, partition it, and then divide via binary fission.

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Microbial Kinetics

The study of microbial growth in controlled conditions.

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Optimal pH

The ideal pH range for most organisms where the concentration of hydrogen ions (H+) and hydroxide ions (OH-) is balanced.

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Acidophiles

Microorganisms that thrive in acidic environments with a pH between 0 and 5.5.

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Neutrophiles

Microorganisms that grow best in neutral environments, with a pH close to 7.

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Minimum Growth Temperature

The lowest temperature at which a microbe can still grow and metabolize.

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Maximum Growth Temperature

The highest temperature at which a microbe can still grow and metabolize.

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Optimal Growth Temperature

The temperature at which microbial growth and metabolism occur at the fastest rate.

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Cardinal Temperatures

The range of temperatures at which a particular microbe can grow, including the minimum, maximum, and optimal temperatures.

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Alkaliphiles

Microorganisms that prefer an alkaline environment with optimal growth between pH 8.5 and 11.5.

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Lethal Temperature

The lowest temperature at which all microorganisms are killed within a specific time.

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Thermoresistance

The ability of a microbe to withstand high temperatures.

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Thermoduric Bacteria

Microorganisms that can survive exposure to temperatures above their maximum growth temperature, often due to spore formation.

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Psychrophiles

Microbes that have an optimal growth temperature between 0°C and 20°C.

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Thermophiles

Microbes that thrive in extremely hot environments, with optimal growth temperatures between 55°C and 85°C.

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Hyperthermophiles

Microorganisms that grow optimally at temperatures above 85°C and can even withstand temperatures above 100°C.

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Protein Stability in Thermophiles

Proteins in thermophiles are stabilized by various adaptations, such as increased hydrogen bonds, more proline residues, and chaperone proteins.

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Membrane Adaptation in Thermophiles

Thermophiles have membrane adaptations, including more saturated and branched lipids with higher molecular weights, and sometimes ether linkages in archaeal membranes.

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Reactive Oxygen Species (ROS)

Oxygen is easily reduced to reactive oxygen species (ROS), like superoxide radical, hydrogen peroxide, and hydroxyl radical, which can be harmful to cells.

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Aerobes

Microorganisms that grow in the presence of oxygen and use it for energy production.

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Strict Anaerobic Microbes

Strict anaerobic microbes lack or have very low levels of superoxide dismutase and catalase, which are essential for detoxifying reactive oxygen species.

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Barotolerant Organisms

Microorganisms that can survive and grow in the presence of increased pressure.

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Barophilic (Piezophilic) Organisms

Microorganisms that require or grow better in the presence of increased pressure.

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Lag Phase

A period of time during microbial growth where an increase in the number of organisms is initially slow.

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Stationary Phase

The phase of microbial growth where the number of viable organisms remains relatively constant.

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Exponential Phase

The phase of microbial growth where the number of living organisms increases exponentially, resulting in a rapid increase in the population.

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Deinococcus radiodurans

Deinococcus radiodurans is highly resistant to DNA damage due to efficient repair mechanisms. It can withstand high doses of radiation and oxidative stress.

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DNA Repair

The process by which a damaged DNA strand is repaired to maintain the integrity of the genetic information.

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UV Radiation Damage

The absorption of UV radiation by DNA can lead to the formation of thymine dimers, which can cause mutations and eventually cell death.

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Viable but Non-Culturable (VBNC) Bacteria

A state where microbes are alive but metabolically inactive and do not divide. They can regain their ability to grow under suitable resuscitation conditions.

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Continuous Culture System

A method for culturing microorganisms where nutrients are continually added and waste products are removed, maintaining the cells in exponential growth phase.

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Fed-batch Culture

A cultivation technique where specific nutrients are added to the bioreactor during the growth process, while products remain in the reactor until the end of the run.

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Growth

The ability of a microorganism to multiply and increase in numbers exponentially.

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Bioreactor

A controlled environment where living organisms are cultivated and their growth can be monitored. It typically involves providing a suitable medium with nutrients and maintaining specific conditions like temperature and pH.

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Biotechnology

The process of using living organisms or their components to produce valuable products or carry out specific tasks.

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Batch Culture

A method for cultivating microorganisms where a specific volume of growth medium is inoculated with cells and allowed to grow without further additions or removals. After a specific period, the products produced by the organisms are harvested.

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Programmed Cell Death

A form of programmed cell death where a fraction of the population is genetically programmed to die.

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Fermentor

A device that provides optimal conditions for the growth of microorganisms. It maintains factors like temperature, pH, and nutrient concentration to support large-scale fermentation.

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Chemostat

A type of controlled continuous culture where the flow rate and concentration of a limiting nutrient are carefully regulated to maintain a steady state.

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Primary Metabolites

Metabolites that are essential for the growth and development of microorganisms. They are produced during the active growth phase of the organism.

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Secondary Metabolites

Products produced by microorganisms typically during the stationary phase of growth. These metabolites are not essential for normal growth but can be valuable for industrial applications.

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Continuous Stirred-Tank Reactor

A completely mixed bioreactor that is used to cultivate cells in a continuous manner, allowing for the maintenance of a controlled environment.

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Study Notes

Microbial Growth

  • Microbial growth is an increase in cellular components, possibly resulting in more cells, or larger cells.
  • Microbiologists study population growth, not the growth of individual cells.

Microbial Growth: Factors

  • Environmental factors:

    • Most microorganisms grow in moderate environments.
    • Extremophiles grow in harsh conditions.

  • Temperature:

    • Microbes cannot regulate internal temperature.
    • Enzymes have optimal temperatures.
    • High temperatures can inhibit enzyme functions and be lethal.
    • Cardinal growth temperatures are minimal, maximal, and optimal.
    • Psychrophiles grow at or below 0°C
    • Psychrotrophs grow at 0-35°C
    • Mesophiles grow at 20-45°C
    • Thermophiles grow over 55°C
    • Hyperthermophiles grow at or above 85°C

  • pH:

    • Enzymes are sensitive to H+ and OH- ion concentrations.
    • Most grow best around a neutral pH (pH 7).
    • Many bacteria prefer slightly alkaline conditions.
    • Many fungi prefer slightly acidic conditions.

  • Oxygen:

    • Some microbes lack or have very low levels of superoxide dismutase and catalase.
    • These microbes cannot tolerate oxygen.
    • Obligate aerobes require oxygen.
    • Facultative anaerobes grow better with oxygen but do not require it.
    • Obligate anaerobes cannot tolerate oxygen.
    • Microaerophiles require low levels of oxygen.

  • Salt:

    • Halophiles grow optimally in the presence of high salt (NaCl) concentrations.
    • Extreme halophiles grow in high salt concentrations (above 2M).
    • Halophiles require high salt concentration.

  • Pressure:

    • Barotolerant microorganisms are adversely affected by increased pressure but not as severely as nontolerant organisms.
    • Barophilic organisms require high pressure to grow more rapidly.
    • Organisms alter their membrane fatty acids to cope with high pressure.

  • Radiation:

    • lonizing radiation (x-rays, gamma rays) causes mutations and cell death.
    • UV radiation causes thymine dimers in DNA.
    • There are mechanisms to repair DNA damage.

Microbial Reproductive Strategies

  • Eukaryotic microbes reproduce both asexually and sexually, in diploid or haploid forms.
  • Bacteria and archaea utilize budding and binary fission.
  • All should replicate and segregate their genome before division.

Bacterial Cell Cycle

  • A sequence of events that result in formation of new daughter cells.
  • Most bacteria divide by binary fission.
  • Two pathways function: DNA replication and partition, and cytokinesis (cell division).

Microbial Growth Curve

  • Four phases in the growth curve:

    • Lag phase
    • Log phase
    • Stationary phase
    • Death phase

  • Lag phase: Initial period immediately after inoculation. Organisms prepare to grow in the new medium (synthesizing enzymes, adjusting to the environment). Cell size may increase but not the population.

  • Log phase: (also called exponential phase or logarithmic phase) exponential increase in population. Cell doubling occurs at a constant rate.

  • Stationary phase: Population growth rate and death rate are equal. Limiting factors may influence growth, like nutrient depletion or the accumulation of toxic waste products.

  • Death phase: Rate of death is faster than growth. Cellular components start breaking down as the microbes die off.

Balanced growth

  • During the log phase, cells all exhibit balanced growth. Growth components/constituent rates are constant proportional to one another.

Possible Reasons for Stationary Stage

  • Limited nutrients
  • Oxygen limitation
  • Accumulation of waste products

Stationary Phase and Starvation Response

  • Entry into stationary phase due to starvation and other factors.
  • Key survival mechanisms are activated such as morphological changes with the production of endospores.

Senescence and Death Phase

  • Bacteria may be alive but not culturable (VBNC). This describes a state where organisms are alive but in a non-dividing, dormant condition.
  • Cell death or programmed cell death (PCD) can occur as a programmed decision to die. This reduces the population of cells through a programmed fraction of the population.

Types of Cultivation

  • Batch culture: A closed system where nothing is added or removed from the system as growth continues.
  • Fed-batch culture: A type of batch culture, where one or more substances are fed into the system over time. Nutrient limitations are less likely to occur in this type of culture.
  • Continuous culture: A system where nutrients are supplied and wastes are continuously removed as the cells grow.

Primary and Secondary Metabolites

  • Primary: Necessary for the growth, development, and reproduction of the organism. Often produced during exponential growth. (e.g., sugars, amino acids, nucleotides, organic acids, vitamins and enzymes).
  • Secondary: Not essential/necessary for growth, produced at or near stationary growth phase (e.g., antibiotics or toxins). These substances are produced in response to environmental conditions.

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