Microbial Growth

• Microbes that are “growing” are increasing in number, accumulating into colonies.
• many bacteria survive and grow slowly in nutrient-poor environments by forming biofilms.
• Growth Factors may require small amounts of certain organic compounds for growth because they are essential substances that the organism is unable to synthesize from available nutrients.
• The requirements for microbial growth can be divided into two main categories: physical and chemical.
• Three physical requirements

  1. Temperature
  2. pH
  3. Osmotic Pressure and Salinity
• Temperature - Most microorganisms grow well at the temperatures that humans favor.
• 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 temperature
• 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 – 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)
• Plasmolysis is 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.
• 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.
• Determine which is hypotonic, isotonic, and hypertonic

  A) isotonic

  B) hypotonic

  C) hypertonic

  
• 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%–10%)
• Organisms that prefer to live in salty environments are called halophilic organisms.
• Extreme Halophiles – 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 are called haloduric organisms
• Barometric Pressure - 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, nitrogen, phosphorus, and sulfur
• Combinations of these and other elements make up vital macromolecules of life, including carbohydrates, lipids, proteins, and nucleic acids.
• Elements such as iron, copper, molybdenum, and zinc serve as trace elements
• Microbes also need organic growth factors for it to grow and survive in its environment.