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</p> Signup and view all the answers

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

    <p>Acidophiles</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.</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.</p> Signup and view all the answers

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

    <p>Neutrophiles</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</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.</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</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</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.</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.</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.</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</p> Signup and view all the answers

    What is the primary method through which most bacteria reproduce?

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

    Which two pathways function during the bacterial cell cycle?

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

    Extreme halophiles require NaCl concentrations of what range to thrive?

    <p>2M to 6.2M</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.</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.</p> Signup and view all the answers

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

    <p>Sexual reproduction</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.</p> Signup and view all the answers

    Which factor could most directly disrupt microbial enzyme function?

    <p>Extreme pH levels</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</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.</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.</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.</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.</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.</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</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.</p> Signup and view all the answers

    What are primary metabolites usually associated with in microorganisms?

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

    Which of the following best describes secondary metabolites?

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

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

    <p>Fermentor</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.</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.</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.</p> Signup and view all the answers

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

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

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

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

    Microorganisms classified as thermoduric are mainly characterized by what trait?

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

    Which adaptation helps stabilize the DNA of thermophiles?

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

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

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

    What effect does ionizing radiation have on microorganisms?

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

    Strict anaerobic microorganisms typically lack which protective enzymes?

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

    Psychrophiles are characterized by their optimal growth temperature range of?

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

    What defines the cardinal temperature range for mesophiles?

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

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

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

    Which environmental condition is commonly associated with oligotrophic environments?

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

    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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