Molecular Aspects of Growth

Question 1

Cells have an ideal ratio of essential elements for optimum growth. What are those essential elements?

Answer 1

carbon, nitrogen, phosphorus

Question 2

What is carbon an essential element for?

Answer 2

-heterotrophs: metabolize organic compounds for carbon + energy
-autotrophs: synthesize organics from CO2

Question 3

What is phosphorus an essential element for?

Answer 3

Nucleic acids, phospholipids, inorganic phosphate (ATP/GTP)

Question 4

What is nitrogen an essential element for?

Answer 4

1. Most microorganisms can use ammonia (NH3)
2. Many can use nitrate (NO3-)
3. Breakdown of proteins, free amino acids
4. Nitrogen-fixing bacteria can use N2

Question 5

How to find the limiting element/resource that drives the entry of bacteria into the stationary phase?

Answer 5

Add up the C:N:P atoms and multiply by the parts and the smallest ratio is the limiting resource

Question 6

What are the two major classes of culture media?

Answer 6

defined and complex

Question 7

What is defined media?

Answer 7

exact chemical composition known

Question 8

What is complex media?

Answer 8

composed or digests of microbial, animal, or plant products

Question 9

What is minimal media?

Answer 9

only supplied the minimal resources needed for growth

Question 10

What is rich media?

Answer 10

supplemented w/ excess resources

Question 11

What is selective media?

Answer 11

exclude specific microbes
Ex: select more growth for gram (+)/(-) bacteria

Question 12

What is differential media?

Answer 12

identify microbes w/ an indicator

Question 13

What are the four methods of growing bacteria?

Answer 13

1. Streak plate
2. Serial dilution
3. Spectrophotometer
4. Microscope

Question 14

Streak plate method

Answer 14

allows isolation of single colonies

Question 15

Serial dilution method

Answer 15

-acquire isolated colonies
-quantify bacteria from liquid culture

Question 16

Spectrophotometer method

Answer 16

-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

Question 17

Microscope method

Answer 17

-hemocytometer: special slide w/ a gridded coverslip
-count cells within each grid
-tedious

Question 18

Pros of serial dilution and plating

Answer 18

-can distinguish living cells from dead cells
-can distinguish cells from debris
-counts still accurate if cell size changes

Question 19

Cons of serial dilution and plating

Answer 19

-dormant cells or viable but not culturable cells (VBNC) will not be counted
-have to wait until colonies grow to get a cell count

Question 20

Pros of spectrophotometry

Answer 20

-quick and easy
-good for high throughput quantification
-semi-quantitative when paired with a standard curve

Question 21

Cons of spectrophotometry

Answer 21

-insensitive to differences in cell size
-cannot distinguish live and dead cells
-if cell count too high, the standard curve is not accurate

Question 22

Pros of microscopy/hemocytometer

Answer 22

-cells can be stained and visualized
-counts still accurate if cell size changes
-VNBC cells are countible

Question 23

Cons of microscopy/hemocytometer

Answer 23

-tedious
-need to clean cover slip
-reload and then count multiple squares