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Bact. 303 Study Questions II

University of Wisconsin - Madison

Nutrition and Growth of Bacteria


37. What are the elemental nutritional requirements of a bacterium? What is the function of each element? What are trace elements and what is their role in bacterial nutrition?

38. Give some examples of organic substances that can be used as carbon and energy sources by bacteria. Give some examples of inorganic chemicals that can be used as either carbon or energy sources by certain bacteria. Besides chemical energy, what other form of energy is commonly available to certain bacteria for growth and metabolism?

39. What are growth factors and what is their role in bacterial nutrition? Name three classes of growth factors? Why are growth factors required in small amounts by cells? What causes the need in a cell for a growth factor?

40. What is a culture medium? Give examples of the types of chemical ingredients in synthetic (chemically-defined) and complex culture media for the growth of bacterial cells. What is meant by the term minimal medium?

41. Define each of the following nutritional classes of bacteria and name some organisms in each class:

  • autotroph
  • lithotroph (chemoautotroph)
  • heterotroph (chemoheterotroph)
  • photoautotroph
  • phototroph
  • 42. Explain the following terms as they relate to a bacterium's response to molecular oxygen (O2).

    43. How is the relationship to O2 similar in metabolism of obligate aerobes and microaerophiles? How is the relationship to O2 different in the metabolism of facultative anaerobes and aerotolerant anaerobes. How is the metabolism of aerotolerant anaerobes and obligate anaerobes similar?

    44. Why can't obligate aerobes grow in the absence of O2? Why can't obligate anaerobes grow in the presence of O2? What is the chemical mechanism of oxygen toxicity in obligate anaerobes? What are the ways that cells have to dispose of toxic oxygen radicals, such as superoxides, singlet oxygen and peroxides, that are inevitably generated by cells in the presence of O2?

    45. What is pH? What effect does pH have on the growth of bacteria? How are bacteria categorized based on their optimal pH for growth. Where in nature are acid-loving bacteria (acidophiles) found?

    46. Draw graphs showing the relationship between temperature and growth rate for each of the following types of bacteria: psychrophile, psychrotroph, mesophile, thermophile, extreme (hyper)thermophile. Give an explanation for the shapes of the curves. What is the approximate range of temperature (degrees) over which each bacterium grows? How are psychrophiles able to grow at temperatures where mesophiles are inhibited. How are thermophiles able to grow at temperatures where most mesophiles are killed? What are the upper and lower temperature limits for the growth of bacteria?

    47. What determines the osmolarity of a bacteriological growth medium? How does osmolarity of the environment affect bacterial growth? What is the relationship between osmolarity and water activity (Aw)? How is Aw expressed? What is the range of Aw over which prokaryotes grow in nature? What is the distinction between an osmotolerant (or halotolerant) organism and an osmophile or (halophile)? Who are the prokaryotes referred to as the "extreme halophiles"?

    48. What is meant by growth of a bacterial cell and growth of a bacterial population? How is bacterial growth measured? Describe several techniques for measuring bacterial growth including microscopic cell counts, viable cell counts, and turbidimetric methods. What are the advantages and disadvantages of each technique?

    49. Draw a typical growth curve for a bacterial population in a closed system (like a test tube). Label the coordinates on the graph. Label each of these phases of the growth cycle: a. lag; b. exponential; c. stationary; d. death. Describe the physiological condition of the cells at each phase of the cycle. Discuss the factors that determine the beginning and end of each phase.

    50. What is the generation time of a bacterial culture? Would you expect generation time to be a constant characteristic of a bacterial species. Explain.

    51. If a fresh culture medium is inoculated with 500 bacterial cells per ml, how many cells will be present after seven generations?

    52. A bacterium having a generation time of 30 minutes will undergo_____cell divisions per hour. During five hours of growth, the cells would double______times. Beginning with 20 cells per ml at time 0, how many cells would be present at 5 hours?

    53. Starting with four bacterial cells in a rich medium with a one-hour lag phase and a 20 minute generation time, how many cells will there be one hour after inoculation of the medium? Two hours after inoculation of the medium?

    54. How long does it take a bacterial culture with a generation time of 12 minutes to increase from 400 cells to 1600 cells per ml?

    55. Distinguish between the following pairs of terms as they are used in microbiology:

  • sterilization and pasteurization
  • bacteriostatic and bactericidal
  • growth factor and growth factor analog
  • antiseptic and disinfectant
  • antibiotic and chemotherapeutic agent

    56. Describe and name some applications for each of the following methods of sterilization:

  • filtration
  • dry heat (hot air oven)
  • autoclave
  • uv irradiation
  • gas (ethylene oxide)

    57. Compare the usefulness of dry heat (hot air oven) and moist heat (autoclave) as means of sterilization. When is boiling effective as a means of sterilization.

    58. What types of materials are generally sterilized by filtration?

    59. What types of chemical substances are used as disinfectants? Antiseptics? Food preservatives?

    60. Why is drying an effective means of preservation. Is its antimicrobial activity microbicidal or microbistatic?

    61. Explain the inhibition of microbial growth brought about by low (refrigeration) temperatures, and the inhibition of growth brought about by the presence of high concentrations of salts or sugars.

    62. What groups of microorganisms are responsible for the industrial production of most antibiotics. What ecological features do these microbes have in common?

    63. What are the five primary modes of action of antimicrobial agents which are in clinical usage. Give important examples of drugs from each category.

    64. Define each of these terms with respect to antimicrobial agents:

  • semisynthetic antibiotic
  • antimetabolite
  • selective toxicity
  • therapeutic index
  • broad spectrum
  • narrow spectrum
  • limited spectrum


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    Edited with Frontier Applications on a Macintosh on Fri, Mar 14, 1997 at 9:06:16 AM by Kenneth Todar University of Wisconsin-Madison Department of Bacteriology.