Molecular Aspects of Growth Flashcards
Cells have an ideal ratio of essential elements for optimum growth. What are those essential elements?
carbon, nitrogen, phosphorus
What is carbon an essential element for?
-heterotrophs: metabolize organic compounds for carbon + energy
-autotrophs: synthesize organics from CO2
What is phosphorus an essential element for?
Nucleic acids, phospholipids, inorganic phosphate (ATP/GTP)
What is nitrogen an essential element for?
- Most microorganisms can use ammonia (NH3)
- Many can use nitrate (NO3-)
- Breakdown of proteins, free amino acids
- Nitrogen-fixing bacteria can use N2
How to find the limiting element/resource that drives the entry of bacteria into the stationary phase?
Add up the C:N:P atoms and multiply by the parts and the smallest ratio is the limiting resource
What are the two major classes of culture media?
defined and complex
What is defined media?
exact chemical composition known
What is complex media?
composed or digests of microbial, animal, or plant products
What is minimal media?
only supplied the minimal resources needed for growth
What is rich media?
supplemented w/ excess resources
What is selective media?
exclude specific microbes
Ex: select more growth for gram (+)/(-) bacteria
What is differential media?
identify microbes w/ an indicator
What are the four methods of growing bacteria?
- Streak plate
- Serial dilution
- Spectrophotometer
- Microscope
Streak plate method
allows isolation of single colonies
Serial dilution method
-acquire isolated colonies
-quantify bacteria from liquid culture
Spectrophotometer method
-cell suspensions are turbid (cloudy) because cells scatter light
-more cells, more light scattered, more turbid suspension
-turbidity measurements are rapid, widely used for estimates
Microscope method
-hemocytometer: special slide w/ a gridded coverslip
-count cells within each grid
-tedious
Pros of serial dilution and plating
-can distinguish living cells from dead cells
-can distinguish cells from debris
-counts still accurate if cell size changes
Cons of serial dilution and plating
-dormant cells or viable but not culturable cells (VBNC) will not be counted
-have to wait until colonies grow to get a cell count
Pros of spectrophotometry
-quick and easy
-good for high throughput quantification
-semi-quantitative when paired with a standard curve
Cons of spectrophotometry
-insensitive to differences in cell size
-cannot distinguish live and dead cells
-if cell count too high, the standard curve is not accurate
Pros of microscopy/hemocytometer
-cells can be stained and visualized
-counts still accurate if cell size changes
-VNBC cells are countible
Cons of microscopy/hemocytometer
-tedious
-need to clean cover slip
-reload and then count multiple squares
