CMB1003/L03 Bacterial Growth

Question 1

Give 3 ways in which recombinant E. coli can be used.

Answer 1

Express proteins for research
Medical
Commercial purposes

Question 2

What can cause bacterial growth to plateau? (2)

Answer 2

Limiting nutrients
Accumulation of toxins

Question 3

What is the ‘lag phase’ of bacterial growth?

Answer 3

Cells adjust to new conditions, synthesis required metabolic enzymes and metabolites

Question 4

What is the ‘exponential phase’ of bacterial growth?

Answer 4

Optimal growth with regular doubling in cell numbers

Question 5

What is the ‘stationary phase’ of bacterial growth?

Answer 5

Growth limited by nutrient depletion or accumulation of toxic metabolites
Rate of new cell production balanced with rate of cell death so no overall growth in cell culture

Question 6

What is the ‘death phase’ of bacterial growth?

Answer 6

Complex gradual loss of viability but with some cell turnover

Question 7

Name 4 methods of measuring bacterial growth.

Answer 7

Plating methods
Turbidity
Direct microscopic counting
Flow cytometry

Question 8

What is the difference between total and viable cell count?

Answer 8

Total cell count includes dead cells
Viable cell count is living cells

Question 9

Describe plating methods. (3)

Answer 9

Culture plated onto solid nutrient medium after serial dilution
Each colony assumed to represent progeny of single viable cell
CFU extrapolated to give cell numbers in original culture

Question 10

Give 2 advantages to plating methods.

Answer 10

Highly sensitive
Growth conditions can be customised so only species of interest grow
Only measure viable cells

Question 11

Give 2 disadvantages to plating methods.

Answer 11

Underestimates for cells in chains or clusters
Number of colonies dependent on growth conditions

Question 12

Describe turbidity methods.

Answer 12

Measures light scattering by cells using a spectrophotometer and a photocell filter

Question 13

Give 2 advantages to turbidity methods.

Answer 13

Simple, convenient
Non-destructive and continuous

Question 14

Give 2 disadvantages to turbidity methods.

Answer 14

Low sensitivity (>10^6 per ml lower limit)
Measures total cell count
Culture turbidity has to be with a range to be accurate

Question 15

Describe direct counting methods.

Answer 15

Count microscopic count of known volume of culture and multiply to amount of volume needed

Question 16

Give an advantage to direct counting methods.

Answer 16

Can accommodate clumping and chaining

Question 17

Give 2 disadvantages to direct counting methods.

Answer 17

Doesn’t discriminate live/dead cells
Laborious (but can be automated)

Question 18

Describe flow cytometry and FACS.

Answer 18

Measure particles in microfluidic flow

Question 19

Give 2 advantages to flow cytometry and FACS.

Answer 19

Highly automated
Can measure fluorescence at multiple wavelengths
Cell sorting possible

Question 20

Give a disadvantage to flow cytometry and FACS.

Answer 20

Requires the correct (expensive) equipment

Question 21

What does FACS stand for?

Answer 21

Fluroescence Activated Cell Sorting

Question 22

How do most bacteria grow?

Answer 22

Binary fission
Elongation and splitting down the middle

Question 23

Describe binary fission. (6)

Answer 23

Cell grows
Cell structures duplicated
Chromosome replicated
Daughter chromosomes segregate to opposite poles
Septum forms mid cell and Z-ring forms
Cell division mid cell

Question 24

What is the start and end point of replication called in plasmids?

Answer 24

OriC and terC

Question 25

How can replication of bacterial chromosomes be described?

Answer 25

Bidirectional from a single origin

Question 26

Describe simply bacterial replication.

Answer 26

Replisomes bind to oriC
Bidirectional replication of DNA
Chromosomes segregate and cells divide

Question 27

How do bacterial cells such as B. subtilis and E. coli overcome the replication conundrum?

Answer 27

Initiating replication in the previous cell cycle

Question 28

What is the Z ring made from?

Answer 28

Z protein and agrin

Question 29

How do cyanobacteria such as Anabaena fix nitrogen and preserve nutrients?

Answer 29

Making differentiated heterocysts (fixing) and akinetes (preserving nutrients)

Question 30

How do Bdellovibrio survive?

Answer 30

Inside other bacteria

Question 31

How do Myxococcus survive?

Answer 31

Eats other bacteria
Makes complex fruiting bodies