Session 7 - Growth

• Many bacteria survive and grow slowly in nutrient-poor environments by forming biofilms.
• The requirements for microbial growth can be divided into two main categories: physical and chemical.
• Physical requirements for Microbial Growth:

  1. Temperature
  2. pH
  3. Osmotic pressure and Salinity
  4. 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


  can thrive at 121°C and above.
• 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.
• 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


  is the pressure that is exerted on a cell membrane by solutions both inside and outside the cell.
• Osmosis


  is the movement of a solvent, through a permeable membrane, from a lower concentration of solutes (dissolved substances) to a higher concentration of solutes.
• When the concentration of solutes in the external environment of a cell is greater than that of solutes inside the cell, the solution in which the cell is suspended is said to be hypertonic.
• Plasmolysis


  a condition in which the cell membrane and cytoplasm of a cell shrink away from the cell wall; it occurs when bacteria with rigid cell walls are placed in a hypertonic solution.
• When the concentration of solutes outside a cell is less than that of solutes inside a cell, the solution in which the cell is suspended is said to be hypotonic.
• If a bacterial cell is placed into a hypotonic solution, it may not burst (because of the rigid cell wall). If it does burst, the cytoplasm escapes; this process is known as plasmoptysis.
• A solution is said to be isotonic when the concentration of solutes outside a cell equals the concentration of solutes inside the cell.
• Organisms that prefer to live in salty environments are called halophilic organisms. Halophilic microbes can be further categorized into:

  • Extreme Halophiles
  • Obligate Halophiles
  • Facultative Halophiles
• Extreme Halophiles

  organisms which require high salt concentration.
• Obligate Halophiles


  require 30% of salt for growth.
• Facultative Halophiles


  requires 15% of salt for growth.
• Microbes that do not prefer to live in salty environments but are capable of surviving there (e.g., Staphylococcus aureus) are called haloduric organisms.
• Microbes that can survive in high atmospheric pressure (>14.7 psi) are known as piezophiles.
• All living protoplasm contains six major chemical elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
• Elements such as iron, copper, molybdenum, and zinc serve as trace elements.
• Combinations of the six major chemical elements and other elements make up vital macromolecules of life, including carbohydrates, lipids, proteins, and nucleic acids.
• Microbes that use molecular oxygen are aerobes while those that do not use oxygen are anaerobes.
• Types of Oxygen Requirement:

  1. Obligate aerobes
  2. Facultative anaerobes
  3. Obligate anaerobes
  4. Aerotolerant anaerobes
  5. Microaerophiles
• 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


  they're aerobic; they do require oxygen. They grow only in oxygen concentrations lower than those in air.
• Capnophiles


  organisms that grow best in the presence of increased concentrations of CO2 (usually 5% to 10%).
• Two types of Asexual Reproduction in Microbes:

  1. Budding division
  2. Binary fission
• Generation time


  When one cell eventually separates to form two cells, we say that one generation has occurred.