Exercise 4: Growth Curve and Diauxic Growth Curve

Question 1

Who referred to the study of bacterial cultures as the “basic method of microbiology”?

Answer 1

Jacques Monod

Question 2

What does the specific growth rate in kinetic models typically depend on?

Answer 2

Growth-limiting nutrient concentration

Question 3

Why are carbon substrates important in microbial growth studies?

Answer 3

Carbon is a major nutrient and often limiting in ecosystems

Question 4

Which organism was studied in the growth kinetics experiment?

Answer 4

Escherichia coli (E. coli)

Question 5

What sugar substrates were used in the E. coli growth experiment? (2)

Answer 5

0.05% glucose and 0.05% lactose

Question 6

In what type of medium was E. coli grown for the experiment?

Answer 6

Minimal medium

Question 7

A biphasic growth pattern when two sugars are used sequentially

Answer 7

Diauxic growth curve

Question 8

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

What happens first in the diauxic growth setup?

Answer 8

E. coli consumes glucose (preferred carbon source).

Question 9

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

What occurs after glucose is consumed in diauxic growth?

Answer 9

Metabolic lag (diauxic lag)

Question 10

Pre-Diauxic Growth Curve and Standard Curve Preparation

What happens after the lag phase?

Answer 10

Pre-Diauxic Growth Curve and Standard Curve Preparation

Question 11

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

Why centrifuge and wash pre-inoculum?

Answer 11

Remove leftover nutrients for a fresh start in minimal media.

Question 12

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

What does OD600 measure?

Answer 12

Turbidity (proxy for cell density).

Question 13

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

Why is OD600 not enough alone?

Answer 13

Doesn’t distinguish live cells; need viable counts.

Question 14

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

How do you create a standard curve?

Answer 14

Plot OD600 vs CFU/mL from known dilutions.

Question 15

PART A: Pre-Diauxic Growth Curve and Standard Curve Preparation

What is the purpose of the standard curve?

Answer 15

Estimate live bacterial counts from OD600 readings.

Question 16

PART B: Diauxic Growth Curve Experiment

Why sample every 30 minutes?

Answer 16

Track population and growth over time.

Question 17

PART B: Diauxic Growth Curve Experiment

Question 18

PART B: Diauxic Growth Curve Experiment

What defines a diauxic growth curve?

Answer 18

Two exponential growth phases separated by a lag.

Question 19

PART B: Diauxic Growth Curve Experiment

What causes the diauxic lag?

Answer 19

Switching gene expression to metabolize lactose (lac operon induction).

Question 20

PART B: Diauxic Growth Curve Experiment

Which carbon source does *E. coli *prefer?

Answer 20

Glucose

Question 21

PART B: Diauxic Growth Curve Experiment

What growth phases do you calculate? (4)

Answer 21

• Lag
• log (exponential)
• stationary
• death

Question 22

PART B: Diauxic Growth Curve Experiment

What growth parameters are derived? (3)

Answer 22

• Generation time
• specific growth rate (μ)
• carrying capacity

Question 23

PART B: Diauxic Growth Curve Experiment

What does this experiment reveal about bacteria? (4)

Answer 23

• Nutrient sensing
• gene regulation
• metabolism link
• real-world growth behavior