LEC #7

• Microbial growth


  Increasing in number, accumulating into colonies
• Bacteria in nutrient-poor environments

  • Survive and grow slowly by forming biofilms
• Growth factors


  Small amounts of certain organic compounds required for growth because they are essential substances that the organism is unable to synthesize from available nutrients
• Requirements for microbial growth

  • Physical
  • Chemical
• Physical requirements

  • Temperature
  • pH
  • Osmotic pressure and salinity
  • Barometric pressure
• Psychrophiles


  Cold-loving microbes living at 0°C
• Psychrotrophs


  A particular group of psychrophiles, prefer refrigerator temperature (4°C)
• Psychroduric microbes


  Prefer warm temperatures but can endure very cold or even freezing temperatures
• Mesophiles


  Moderate temperature-loving microbes withstanding 25 to 40°C; the most common type of microbe
• Thermophiles

  Heat-loving microbes withstanding 50 to 60°C
• Hyperthermophiles

  Have an optimum growth temperature of 80°C or higher
• Extreme thermophiles

  121°C and above
• pH

  Acidity or alkalinity of a solution
• Acidophiles

  Bacteria that loves acidic environment (pH of 2 to 5)
• Alkaliphiles

  Bacteria that loves basic or alkaline environment (pH of >8.5)
• Osmotic pressure

  Pressure exerted on a cell membrane by solutions both inside and outside the cell
• Osmosis

  Movement of a solvent, through a permeable membrane, from a lower concentration of solutes to a higher concentration of solutes
• Hypertonic

  When the concentration of solutes in the external environment of a cell is greater than that of solutes inside the cell
• Plasmolysis

  Condition in which the cell membrane and cytoplasm of a cell shrink away from the cell wall; occurs when bacteria with rigid cell walls are placed in a hypertonic solution
• Hypotonic

  When the concentration of solutes outside a cell is less than that of solutes inside the cell
• Plasmoptysis

  Process where the cytoplasm escapes when a bacterial cell placed in a hypotonic solution bursts
• Isotonic

  When the concentration of solutes outside a cell equals the concentration of solutes inside the cell
• Halophilic organisms

  Organisms that prefer to live in salty environments
• Halophilic microbes

  • Extreme Halophiles
  • Obligate Halophiles
  • Facultative Halophiles
• Haloduric organisms

  Microbes that do not prefer to live in salty environments but are capable of surviving there
• Piezophiles

  Microbes that can survive in high atmospheric pressure (>14.7 psi)
• Chemical requirements

  • Major chemical elements (carbon, hydrogen, nitrogen, phosphorus, sulfur)
  • Trace elements (iron, copper, molybdenum, zinc)
  • Organic growth factors
  • Oxygen requirement
• Obligate aerobes

  Organisms that require oxygen to live
• Facultative anaerobes

  Microbes that can grow in the absence of oxygen
• Obligate anaerobes

  Microbes that are unable to use molecular oxygen for energy-yielding reactions
• Aerotolerant anaerobes

  Cannot use oxygen for growth, but they tolerate it fairly well
• Microaerophiles

  Aerobic, require oxygen but only in concentrations lower than those in air
• Capnophiles

  Organisms that grow best in the presence of increased concentrations of CO2 (usually 5%-10%)
• Categories of microbes based on oxygen relationship

  • Obligate aerobes
  • Facultative anaerobes
  • Obligate anaerobes
  • Aerotolerant anaerobes
  • Microaerophiles
• Types of asexual reproduction in microbes

  • Binary fission
  • Budding division
• Generation time

  Time for one cell to separate to form two cells
• Biofilms

  Attached polysaccharide matrix containing embedded bacterial cells
• Types of culture media

  • Defined media
  • Complex media
• Phases of microbial growth cycle

  • Lag phase
  • Exponential or log phase
  • Stationary phase
  • Death phase
• Exponential growth

  Repetitive pattern where the number of cells doubles in a constant time interval