microbial growth

    Cards (65)

    • Microbial Growth
      Increase in number of cells (not the size of cells)
    • Growing microbes accumulate into colonies
    • In nutrient poor environments, they form biofilms
    • Significance of microbial growth topic
      • By understanding the conditions necessary for microbial growth, we can determine how to control the growth of microbes that cause diseases and food spoilage
      • We can also learn how to encourage the growth of helpful microbes and those we wish to study
    • Requirements for growth
      • Physical requirements
      • Chemical requirements
    • Physical requirements
      • Temperature
      • pH
      • Osmotic pressure
    • Chemical requirements
      • Carbon
      • Nitrogen
      • Sulfur
      • Phosphorus
      • Trace Elements
      • Oxygen
      • Organic Growth Factors
    • Temperature
      • Most microorganisms grow well at temperatures that humans favor, while some thrive at extremes of temperatures
      • Most bacteria grow only within a limited range of temperatures with their maximum and minimum growth temperatures only approx. 30qC apart
    • Microbial classification by preferred range of temperature
      • Psychrophiles (cold loving)
      • Mesophiles (moderate temperature)
      • Thermophiles (heat loving)
    • Minimum growth temperature
      The lowest temperature at which a microorganism can grow
    • Optimum growth temperature
      The temperature at which a microorganism grows best
    • Maximum growth temperature
      The highest temperature at which a microorganism can grow
    • Refrigeration is the most common method of food preservation as low temperatures decrease microbial reproduction rates
    • Refrigerating rice in a pot half-full

      Versus transferring to and flattening it in a wider plate or pan
    • pH
      Refers to the acidity or alkalinity of a solution
    • Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5
    • Pickled foods
      Foods preserved from spoilage by acids produced by bacterial fermentation
    • Acidophiles
      Microorganisms that tolerate acidity and thrive in lower pH levels
    • Molds & yeasts grow over a greater pH range than bacteria, but their optimum pH is about 5 to 6
    • Chemical buffers
      Chemicals added to the growth medium used to neutralize the acids and maintain proper pH
    • Chemical buffers help maintain proper pH despite changes in pH
    • Osmotic pressure
      The pressure that causes water to move across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration
    • Microorganisms require water for growth and even obtain almost all their nutrients in solution from the surrounding water
    • Hypertonic solution

      A solution with a higher concentration of solutes than the cell, causing water to leak out of the cell (plasmolysis)
    • Plasmolysis
      The shrinkage of a cell's cytoplasm due to osmotic loss of water, inhibiting cell growth
    • The high salt or sugar concentrations in salted or sweetened foods draw water out of any microbial cells that are present and thus prevent their growth
    • Adaptations to different salt concentrations
      • Obligate/extreme halophiles (thrive in high salt, require it for growth)
      • Facultative halophiles (able to grow at salt concentrations up to 2%)
    • Hypotonic environment

      An environment with very low osmotic pressure, causing water to enter the cell and potentially lyse it (cytolysis)
    • Carbon is the structural backbone of living matter, needed for all the organic compounds that make up a living cell, or provide energy source
    • Chemoheterotrophs
      Organisms that get most of their carbon from organic materials such as proteins, carbohydrates, and lipids
    • Autotrophs
      Organisms that derive their carbon from CO2
    • Nitrogen, Sulfur, Phosphorus
      Important for protein synthesis, DNA/RNA synthesis, and ATP synthesis
    • Nitrogen acquisition
      • Decomposition of proteins & reincorporation
      • Acquisition of ammonium ions (NH4+) from organic material
      • Nitrogen fixation (directly use gaseous nitrogen (N2) from the atmosphere)
    • Sulfur is used to synthesize sulfur-containing amino acids & vitamins such as thiamine & biotin
    • Phosphorus is essential for the synthesis of nucleic acids and the phospholipids of cell membranes, and is also found in the energy bonds of ATP
    • Trace elements such as iron, copper, molybdenum, and zinc are required in very small amounts, usually as cofactors for enzymes
    • Aerobic respiration

      Metabolic system that requires oxygen as the final electron acceptor, extracting more energy from nutrients than anaerobic respiration
    • Classification based on need for oxygen
      • Obligate aerobes
      • Microaerophiles
      • Facultative anaerobes
      • Aerotolerant anaerobes
      • Obligate anaerobes
    • Oxygen is actually toxic in its reactive forms (singlet oxygen, superoxide radicals, peroxide anion, hydroxyl radical)
    • Organic growth factors
      Essential organic compounds that an organism is unable to synthesize and must directly obtain from the environment, including vitamins, essential amino acids, and purines & pyrimidines
    See similar decks