Lecture 1

Question 1

Characteristics of Prokaryotes

Answer 1

• No defined nucleus
• no membrane bound organelles
  70S ribosomes (50s large subunit + 30s small subunit)
  diverse metabolism
  transport systems in cell membrane
  replicate asexually by binary fission

Question 2

What is a batch culture

Answer 2

closed system where cells are grown in a medium with specific nutrients under specific environmental conditions.

Question 3

What are the 5 phases of growth in batch culture

Answer 3

1) Lag phase
2) Log/exponential phase
3) Stationary phase
4) Death phase
5) Long-term stationary phase

Question 4

What happens in the Lag phase?

Answer 4

Cells are adapting to the new medium and synthesising new components. This phase varies in length, being very short or even non-existent.

Question 5

What happens in the Log/exponential phase?

Answer 5

Cells are dividing and growing at a constant, maximal rate.
The population is quite uniform in chemical and physical properties and cells grow as quickly as they can given the conditions available to them.

Question 6

What happens in the stationary phase?

Answer 6

Conditions become limiting and growth rates slow as the total number of viable cells remains constant.
Active cells stop reproducing or reproductive rate becomes balanced by death rate.

Question 7

What are some possible reasons for the stationary phase?

Answer 7

• nutrient limitations
• Limited oxygen availability
• toxic waste accumulation
• critical population density reached

Question 8

What happens in the death phase?

Answer 8

Two possible hypotheses
1) cells are viable but not culturable (VBNC)
(alive but dormant, capable of new growth when conditions become right)

2) Programmed cell death - fraction of population genetically programmed to die (decline in viable cells in population)

Question 9

What happens in the long term stationary phase?

Answer 9

Prolonged decline in growth.

Successive waves of genetically distinct variance. Natural selection occurs.

Question 10

How can you measure cell mass?

Answer 10

Using a spectrophotometer at a wavelength of ~600nm the optical density of the bacterial culture can be found

The higher the cell density the more light the cells will absorb and the less light will pass to the detector.

The more cells in a culture the more light they will absorb and less light will pass to the detector.
However larger cells will absorb more light to to estimate the number of cells, the spectrophotometer must be calibrated for each species and can change with culture conditions

Question 11

How do you describe colony morphologies?

Answer 11

Form, elevation and margin