Chapter 4 Flashcards
Microbial growth:
Increase in number of cells, not cell size. Growth in population size.
Colony-forming units:
On plate counts. Visible bacterial colonies on solid media.
Serial Dilutions:
Used for plate counting, used to decrease a bacterial concentration to a required concentration for a specific test method, or to a concentration which is easier to count when plated to an agar plate.
Turbidity:
Most common method of cell counting.
Measured with a Spectrophotometry: Bacteria scatter light, based on their density, measured as optical density (OD), OD correlated with biomass and counts from viable counts. Only absorbance needs to be measured (very rapid).
Percentage of transmission
Used for large amounts of bacteria, need 10 million to 100 million cells per milliliter to read – not for detecting contaminants
Endospores:
Sporulation:
Germination:
Resting cells; produced when nutrients are depleted, resistant to desiccation, heat, chemicals, and radiation. Readily spread.
Produced by Bacillus and Clostridium
Sporulation: endospore formation
Germination: spore returns to vegetative state
NOT REPRODUCTION
Balanced Growth:
All cells constituents increase by the same proportion over any given interval of time
Chemostat:
Growth rate determined by addition of medium
Cell density is constant, limiting nutrient. Used for performing long experiments- good for studying evolution of microbes. Large scale industrial fermentations.
Extremophiles:
Thrive under extreme conditions.
Temperature, hydrostatic pressure, osmotic pressure, pH, oxygen, radiation.
Plasmolysis:
Caused by hypertonic environments, or an increase in salt or sugar.
Plasmolysis is the process in which cells lose water when they are placed in a hypertonic solution. It causes contraction or shrinking of the plasma membrane away from the cell wall. It is a reversible process and the cell can get back to normal when placed in a hypotonic solution
Determining cell numbers: Counting of cells and determination of mass/density of the cell
Counting microbial cells:
direct counting (microscope), flow cytometer, viable counts (spread plate, pour plate), filtration.
Determining mass/density:
weighing, spectrophtometry (turbidity).
Direct count of cells:
Microscope and counting chamber. Requires dense cultures, number of cells per unit area (proportional to volume), counts both living and dead cells.
Flow cytometer for counting cells:
Faster and automated. Total particle count. Counts and analyzes the size, shape, surface topography, internal complexity, sorts. Counts living and dead cells.
Viable counts:
Spread plate and Pour plate
Uses serial dilutions, plated on medium to get 30 to 300 colonies per plate. Allows for calculation of number of cells per ml based on dilution.
Plate counts:
Takes 24 or more hours, only counts viable cells, colony forming units, 30-300 colonies.
Membrane Filtration for counting bacteria:
For small quantity of bacteria (like in lakes or relatively pure streams). Water passed through a thin membrane filter
Cell weight:
For mold and filamentous bacteria, direct weighing of dried cell mass (removed from media, dried, weighed).
Four Basic phases of bacterial growth:
- Lag; initially no increase in cell numbers, synthesis of new enzymes required for growth.
- Exponential; number of cells double each division.
- Stationary; Slowed growth rate, nutrients exhausted. waste products accumulate, other conditions not optimal for growth (growth=death).
- Death; cells die due to accumulation of toxins. Death exceeds the number of new cells formed.
What are the three equations of microbial growth?
Law of growth: N=(2^n)No
Generation number: logN-logNo/log2
Generation time: [g]=t/n
Generation time:
Minimum growth temperature, optimum growth temperature, maximum growth temperature:
- Minimum growth temperature – lowest temp at which the species will grow
- Optimum growth temperature – highest
growth rate - Maximum growth temperature – highest
temp at which the species will grow
What is the growth range of microbes?
-15 ºC to 121 ºC.
Basically any condition with liquid water.
Psychrophiles
Typically grow at 5ºC
Psychrophiles exist at lower to extreme low temperatures, ranging from 5°C to 15°C or lower. It can grow even up to the freezing point of water. They are found in freezing environments, such as glaciers, deep oceans, and polar regions.
The smaller the cell, the _ it grows
The faster it grows.
Mesophiles:
Typically grows at 37ºC.
Mesophiles are microorganisms which grow at moderate temperatures between 20 °C and 45 °C and with an optimum growth temperature in the range of 30–39 °C. They are isolated in both soil and water environments; species are found in the Bacteria, Eukarya, and Archaea kingdom
