Chapter 5 Lec.2

Question 1

Microbial growth cycle

Answer 1

Batch culture: closed system of microbial growth

Growth curve: lag, exponential, stationary and death phases.

Question 2

Microbial growth implications

Answer 2

Pattern of population increase

-Initially slow then more rapidly.

Question 3

Growth cycle: Lag Phase

Answer 3

Lag phase: Microbes absorb nutrients, synthesize enzymes and prepare for cell division.

Question 4

Growth cycle: exponential phase

Answer 4

During exponential phase, cells exhibit balanced growth.

• time of maximum growth.
• Population doubles during each generation time.
• Varies with species.

Question 5

Growth cycle: stationary phase

Answer 5

Occurs when microbes dying equals number dividing.
-May be due to nutrients, O2…

Entry into stationary phase due to starvation and other stressful conditions activates survival strategy.
-morphological changes

Question 6

Growth phase: death cycle

Answer 6

Death phase starts when the population starts decreasing.

-depletion of resources and waste buildup.

Question 7

Continuous culture: The chemostat

Answer 7

Nutrients constantly supplied and waste products flushed out.
Growth rate and population density of culture controlled.
CHEMOSTAT-type of continuous culture.

Question 8

Why use a continuous culture vs. a batch culture?

Answer 8

Precise control of cell growth rates/density.

Able to maintain cell growth in exponential phase.

Question 9

Measuring microbial growth

Answer 9

4 methods:

• microscopic count
• automatic cell count
• viable count
• turbidimetry

Question 10

Microscopic counts

Answer 10

Microbial cells are enumerated by microscopic observations

-results can be unreliable

Question 11

Limitations of microscopic counts

Answer 11

Cannot distinguish between dead and alive cells.
Small cells can be overlooked.
Precision is difficult.
Phase-contrast microscope required if a stain isn’t used.
Motile need to be immobilized.

Question 12

Automatic cell counts

Answer 12

Method for enumerating cells in liquid samples with flow cytometer.
-Uses lasers, dyes and electronics.

Question 13

Plate counts

Answer 13

Measurement of living, reproducing population.
Microbes grown on plates.
-Serial dilution

Question 14

Viable cell counting: The great plate anomaly

Answer 14

Direct microscopic counts of natural samples reveal far more organisms than those recoverable on plates.
Why is this?
-Microscopic methods count dead cells whereas viable methods do not.
-Different organisms have different requirements.

Question 15

Turbidimetric methods

Answer 15

Turbidity measurements are indirect but very rapid and useful.

Question 16

Turbidimetric advantages

Answer 16

Quick and easy to perform.

Does not require disturbance or destruction of sample.

Question 17

Factors regulating growth

Answer 17

Nutrients
Environmental conditions:
-pH
-Temp
-osmotic pressure
Generation time.

Question 18

Extremophiles

Answer 18

Grow under harsh conditions.

Question 19

Temperature

Answer 19

Microbes cannot regulate their internal temperature.
Enzymes have optimal temperature where they function.
High temperatures may inhibit enzyme functioning.

Question 20

Cardinal growth temperature

Answer 20

• Min
• Optimal
• Max

Question 21

Temperature Ranges for microbial growth

Answer 21

Psychrophiles- 0-20C
Mesophiels- 20-45C
Thermophiles- 55-85C
Hyperthermophiles- 85-113C

Question 22

Mesophile

Answer 22

Organisms that have midrange temperature requirements, found in:

• animals
• terrestrial and aquatic environments

Question 23

Psychrophiles

Answer 23

Organisms with cold temp optima.

-Inhabit cold environments.

Question 24

Psychrotolerant

Answer 24

Organisms that can grow at 0 but have an optima in the 20-40 range.