Microbial Growth

• Microbial growth is increasing in number, accumulating into colonies
• Biofilms is attached polysaccharide matrix containing embedded bacterial cells
• Growth factors is 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
• Psychrophiles: Cold-loving microbes living at 0°C
• Psychrotrophs: 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 is 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 is pressure exerted on a cell membrane by solutions both inside and outside the cell
• Osmosis is movement of a solvent, through a permeable membrane, from a lower concentration of solutes to a higher concentration of solutes
• Hypertonic is when the concentration of solutes in the external environment of a cell is greater than that of solutes inside the cell
• Plasmolysis is 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 is when the concentration of solutes outside a cell is less than that of solutes inside a cell
• Plasmoptysis is process where the cytoplasm escapes when a bacterial cell placed in a hypotonic solution bursts
• Isotonic is when the concentration of solutes outside a cell equals the concentration of solutes inside the cell
• Extreme Halophiles: Require high salt concentration
• Obligate Halophiles: Require 30% of salt for growth
• Facultative Halophiles: Requires 15% of salt for growth
• Haloduric organisms is 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)
• Major chemical elements in living protoplasm: Carbon, Hydrogen, Nitrogen, Phosphorus, Sulfur
• Trace elements is elements such as iron, copper, molybdenum, and zinc that serve as micronutrients
• Organic growth factors is required for microbes to grow and survive in their environment
• Types of oxygen requirement: Obligate aerobes, Facultative anaerobes, Obligate anaerobes, Aerotolerant anaerobes, Microaerophiles, Capnophiles
• Binary fission is forms a totally new daughter cell, with the mother cell retaining its original identity
• Budding division forms a totally new daughter cell, with the mother cell retaining its original identity
• Generation time is when one cell eventually separates to form two cells, one generation has occurred
• Culture medium or growth medium is liquid or gel designed to support the growth of microorganisms
• 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 is repetitive pattern where the number of cells doubles in a constant time interval
• Chemostat is the most common type of continuous culture system where a known volume of sterile medium is added at a constant rate while an equal volume of spent culture medium is removed at the same rate
• Methods for measuring number of microbes: Microscopic counting, Plate count, Serial dilution, Filtration, Most Probable Number (MPN) method, Direct microscopic count, Coulter counter, Turbidity, Metabolic activity, Dry weight
• Plate count is most frequently used method of measuring bacterial populations, often reported as colony-forming units (CFU)