Micro Chapter 6: Microbial Growth

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Micro Chapter 6: Microbial Growth
2011-06-18 00:19:19

Chapter 6
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  1. Mother cell divides into
    two daughter cells
  2. Microbial growth
    the increase in the number of cells, which occurs by cell division
  3. Binary fission
    a cell duplicates its components and divides into two cells
  4. Budding
    cell division in yeast and a few bacteria where a small, new cell develops from the surface of an existing cell and subsequently separates from the parent cell
  5. Medium
    mixture of substances on or in which microorganisms grow
  6. The Lag Phase
  7. a. The organisms do not increase significantly in number, but they are metabolically active – growing in size, synthesizing enzymes, and incorporating various molecules from the medium
    b. Increase in size and produce large quantities of ATP
  8. The Log Phase
    • a. Population growth occurs at an exponential, or logarithmic (log) rate
    • b. Organisms divide at their most rapid rate
  9. Generation time
    regular, genetically determined interval
  10. Synchronous growth
    stair-step pattern
  11. Nonsynchronous growth
    1/20 of cells dividing every minute
  12. Limiting factor
    the rate at which energy can be produced in the form of ATP
  13. The Stationary Phase
    When cell division decreases to the point that new cells are produced at the same rate as old cells die
  14. The Decline (death) Phase
    • a. As conditions in the medium become less and less supportive of cell division, many cells lose their ability to divide, and thus the cells die
    • b. Decreases at a logarithmic rate
  15. Involution
    cells assume a variety of unusual shapes, which makes them difficult to identify
  16. Colony
    all the descendants of an original cell
  17. Agar plate
    a Petri dish containing a nutrient medium solidified with agar (a complex polysaccharide extracted from certain marine algae)
  18. Countable number of colonies
    is 30 – 300 per plate
  19. Direct Microscopic Counts
    Uses a specially calibrated, etched glass slide called a Petroff-Hausser counting chamber (hemocytometer)
  20. Most Probable Number
  21. 1. When samples contain too few organisms to give reliable measures of population size (food and water sanitation studies)
    2. Dilute to where some test tubes contain 1 organisms and some none (testing water purity)
  22. Filtration
    A known volume of water or air is drawn through a filter with holes too small to allow passage of bacteria
  23. Turbidity
    indicates presence of organisms

    • a. Spectrophotometer
    • b. Subject to error when cultures contain fewer than 1 million cells per milliliter
  24. For almost any substance, there is some microbe that can metabolize it as a nutrient; for almost any environmental change, there is some microbe that can survive the change
  25. Physical Factors
    Include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure, and radiation
  26. optimum pH
    the pH at which microbes grow best
  27. acidophiles
    grow best at a pH of 0.1 to 5.4 (Lactobacillus)
  28. neutrophiles
    exist from pH 5.4 to 8.0
  29. alkaliphiles
    exist from pH 7.0 to 11.5 (Vibrio cholera grows best at pH 9.0)
  30. Obligate
    the organism must have the specified environmental condition
  31. Facultative
    the organism is able to adjust to and tolerate the environmental condition, but it can also live in other conditions
  32. Psychrophiles
    (cold-loving organisms) grow best at temperatures of 15* to 20*C, although some live quite well at 0*C
  33. Obligate psychrophiles
    (Bacillus globisporus) cannot grow above 20*C
  34. Faciltative psychrophiles
    (Xanthomonas pharmicola) grows best below 20*C but can grow above that temperature
  35. Mesophiles
    grow best at temperatures between 25* and 40*C.

    Human pathogens
  36. Thermoduric organisms
    ordinarily live as mesophiles but can withstand short periods of exposure to high temperatures
  37. Thermophiles
    (heat-loving organisms) grow best from 50* to 60*C
  38. Obligate thermophiles
    can grow only at temperatures above 37*C
  39. Facultative thermophiles
    can grow both above and below 37*C
  40. Minimum growth temperature
    the lowest temperature at which cells can divide
  41. Maximum growth temperature
    the highest temperature at which cells can divide
  42. Optimum growth temperature
    the temperature at which cells divide most rapidly
  43. Obligate aerobes
    (Pseudomonas) must have free oxygen for aerobic respiration
  44. Obligate anerobes
    (Clostridium botulinum, C. tetani, and Bacteroides) are killed by free oxygen

    a. Killed by superoxide
  45. Microaerophiles
    appear to grow best in the presence of a small amount of free oxygen
  46. Capnophiles
    carbon dioxide-loving organisms
  47. Facultative anaerobes
    ordinarily carry on aerobic metabolism when oxygen is present, but they shift to anaerobic metabolism when oxygen is absent (Staphylococcus and E. Coli)

    Have the most complex enzyme systems
  48. Aerotolerant anaerobes
    can survive in the presence of oxygen but do not use it in their metabolism
  49. Hydrostatic Pressure
    Pressure exerted by standing water, in proportion to its depth
  50. Barophiles
    bacteria that lice at high pressures, but die in atmospheric pressure
  51. Plasmolysis
    shrinking of the cell
  52. Halophiles
    salt-loving organisms
  53. Bacteria which can withstand high levels of radiation may be valuable for use in cleaning up contaminated sites
  54. Fastidious
    microbes that have special nutritional needs that can be difficult to meet in the laboratory
  55. Photoautotrophic organism reduce carbon dioxide to
    glucose and other organic molecules
  56. Some microbes reduce nitrate ions to
    amino groups
  57. Some organisms synthesize sulfur-containing amino acids and they use phosphorus to
    synthesize ATP, phospholipids, and nucleic acids
  58. Vitamin
    an organic substance that an organism requires in small amounts and that is typically used as a coenzyme
  59. Nutritional Complexity
    The number of nutrients it must obtain to grow
  60. Extracellular enzymes
    usually produces by Gram-positive rods, which act in the medium around the organism
  61. Periplasmic enzymes
    usually produced by Gram-negative organisms, which act in the periplasmic space
  62. Many organisms adjust the rate at which _____________ and the rate at which _____________ to fit the availability of the lease plentiful nutrient
    they metabolize nutrients

    they synthesize molecules required for growth
  63. The formation of endospores occurs in _______ .
    Bacillus, Clostridium, and a few other Gram-positive genera.
  64. Bacteria that form endospores generally do so during the __________ in response to environmental, metabolic, and cell cycle signals
    stationary phase
  65. Sporulation
    Protective or survival mechanism, not a means of reproduction
  66. Core
    living part of the endospore
  67. Endospore septum
    consisting of a cell membrane but lacking a cell wall, grows around the core, enclosing it in a double thickness of cell membrane (synthesizes peptidoglycan)
  68. Cortex
    protects the core against changes in osmotic pressure (drying)
  69. Spore coat
    is laid down around the cortex by the mother cell
  70. Exosporium
    a lipid-protein membrane
  71. Germination
    a spore returns to its vegetative state
  72. Germination Activation
    usually requires some traumatic agent such as low pH or heat, which damages the coat
  73. Germination proper
    requires water and a germination agent that penetrates the damaged coat
  74. Germination Outgrowth
    occurs in a medium with adequate nutrients. Proteins and RNA are synthesized, and in about an hour, DNA synthesis begins
  75. Cysts
    spherical, thick-walled cells, that resemble endospores

    Metabolically inactive and resist drying
  76. Conidia
    chains of aerial spores with thick outer walls
  77. Pure culture
    a culture that contains only a single species of organism
  78. The Pour Plate Method
  79. 1. Makes use of serial dilutions
    • a. A series of dilutions are made such that the final dilution contains about 1,000 organisms
    • b. It is particularly useful for growing microaerophiles that cannot tolerate exposure to oxygen in the air at the surface of the medium
  80. Synthetic medium
    a medium prepared in the laboratory from materials of precise or reasonable well-defined composition
  81. Defined synthetic medium
    one that contains known specific kinds and amounts of chemical substances
  82. Complex medium (chemically nondefined medium)
    contains reasonable familiar materials but varies slightly in chemical composition from batch to batch
  83. Peptone
    a product of enzyme digestion of proteins, common ingredient of complex medium
  84. Casein hydrolysate
    made from mil protein, contains many amino acids and is used to enrich certain media
  85. Selective medium
    one that encourages the growth of some organisms but suppresses the growth of others (SPS agar)
  86. Differential medium
    has a constituent that causes an observable change ( a color change or a change in pH) in the medium when a particular biochemical reaction occurs
  87. Enrichment medium
    contains special nutrients that allow growth of a particular organism that might not otherwise be present in sufficient numbers to allow it to be isolated and identified
  88. Stock culture
    one an organism has been isolated, it can be maintained indefinitely in a pure culture
  89. Aseptic techniques
    minimize the chances that cultures will be contaminated by organisms from the environment or that organism, especially pathogens, will escape into the environment
  90. Preserved Cultures
    A culture in which organisms are maintained in a dormant state
  91. Lyophilization
  92. Reference culture
    a preserved culture that maintains the organisms with the characteristics as originally defined