micp

• All living organisms require nutrients to sustain life
• Nutrients are energy sources
• Organisms obtain energy by breaking chemical bonds
• Water is essential for life. It is needed to carry out normal metabolic processes
• Certain microbial stages (e.g., bacterial endospores and protozoal cysts) can survive a drying process (desiccation).
• Every organism has an optimum growth temperature
• The temperature (and pH) ranges over which an organism grows best are largely determined by its enzymes
• Thermophiles are microorganisms that grow best at high temperatures
• Mesophiles are microbes that grow best at moderate temperatures (e.g., 37o C)
• Psychrophiles prefer cold temperatures (like deep ocean water)
• Psychrotrophs, a particular group of psychrophiles, prefer refrigerator temperature (4oC)
• Psychroduric organisms prefer warm temperatures, but can endure very cold or even freezing temperatures
• pH refers to the acidity or alkalinity of a solution
• Most microorganisms prefer a neutral or slightly alkaline growth medium (pH 7.0 - 7.4)
• Acidophiles prefer a pH of 2 to 5
• Alkaliphiles prefer a pH > 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 is a 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 into 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
• Those that do not prefer to live in salty environments, but which 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 know as piezophiles
• Microorganisms vary with respect to the type of gaseous atmosphere that they require.
• Obligate aerobes prefer the same atmosphere that humans do (~20-21% O2 and 78-79% N2 , other gases < 1%).
• Microaerophiles require reduced concentrations of oxygen (~5% O2 ).
• Obligate anaerobes are killed by the presence of oxygen.
• Capnophiles require increased concentrations of CO2 (5-10% CO2 ).
• Think of bacterial growth as an increase in the number of organisms rather than an increase in their size.
• Bacteria divide by binary fission (one cell divides to become two cells) when they reach their optimum size.
• Binary fission continues through many generations until a colony is produced on solid culture medium.
• Binary fission continues for as long as there is a sufficient supply of nutrients, water, and space.
• The time it takes for one cell to become two cells is called the generation time (e.g., E. coli = 20 minutes).
• Media are used in microbiology labs to culture bacteria
• media prepared in the lab are referred to as artificial media or synthetic media
• A chemically defined medium is one in which all ingredients are known
• Culture media can be liquid or solid.