Topic 5: Control of Microbial Growth

Question 1

Psychrophiles

Answer 1

Range of -5 to 20 degrees celsius, optimum at 15 degrees celsius
- Ex: deep-ocean microbes

Question 2

Psychrotrophs

Answer 2

Range of 0 to 45 degrees celsius, optimum 20 degrees to 30 celsius
- Ex: Pseudomonas

Question 3

Mesophiles

Answer 3

Range of 12 to 48 degrees celsius , optimum 25 to 40 degrees celsius
- E.g. Salmonella

Question 4

Thermophiles

Answer 4

Range of 42 to 68 degrees celsius, optimum 50 to 60 degrees celsius
- Ex: hot water pipes, hot springs

Question 5

Extreme thermophiles

Answer 5

Archaea
- 80 degrees celsius
Ex: Deep sea vents

Question 6

Optimum pH range for most bacteria

Answer 6

6.5 to 7.5

5-6 for molds and yeasts

Question 7

What happens when bacteria are subjected to a hypertonic environment?

Answer 7

They will experience plasmolysis

- Does not kill the bacteria but they cannot metabolize or grow

Question 8

Halophiles

Answer 8

They prefer or require high salt concentrations

Mostly Archaea

Question 9

What happens when bacteria are placed in a hypotonic environment?

Answer 9

Mostly protected from lysis by their cell wall

Question 10

Chemical requirements of bacteria

Answer 10

• water
• carbon source
• source of nitrogen, sulfur, and phosphorous

Question 11

How do bacteria obtain nitrogen?

Answer 11

Catabolism of amino acids or nitrogen fixation

needed primarily for amino acids

Question 12

How do bacteria obtain phosphorous?

Answer 12

From Po4 (-3) in the environment 
- often a limiting factor to growth

Question 13

Obligate aerobe

Answer 13

Must have oxygen

- O2 as a terminal electron acceptor

Question 14

Obligate anaerobe

Answer 14

Must be protected from oxygen

Question 15

Facultative anaerobes

Answer 15

Usually generate ATP through respiration with oxygen but they can still metabolize without oxygen

Question 16

Aerotolerant anaerobes

Answer 16

Don’t use O2 to make ATP but can deal with O2 toxicity

Question 17

Microaerophiles

Answer 17

Need O2 to make ATP but have weak defence against toxicity

Question 18

Oxygen toxicity

Answer 18

Sometimes superoxide free radicals are produced with oxygen

- Free radicals cause damage

Question 19

Biofilms

Answer 19

A macroscopic community with other bacteria that adhere to the surface

Question 20

Culture

Answer 20

Microbes growing in/on culture medium, usually of one strain only

Question 21

Culture medium

Answer 21

Nutrients and substrate prepared for microbial growth

Question 22

Agar

Answer 22

Seaweed polysaccharide

Question 23

Chemically defined medium

Answer 23

The exact proportions of specific nutrients are tightly controlled

Question 24

Complex medium

Answer 24

The exact composition of the various nutrients unknown

made with things like beef extract

Question 25

MacConkey’s agar

Answer 25

Inhibits gram positive bacteria

- Uses bile salts & crystal violet

Question 26

Blood agar

Answer 26

Used for Streptococcus

Question 27

Phases of growth of a bacterial culture

Answer 27

1. Lag phase
2. Log phase
3. Stationary phase
4. Death phase

Question 28

Lag phase

Answer 28

Cells are getting use to a new medium and grow slowly

Question 29

Log phase

Answer 29

Rate of growth is maximum

- Rate of cell division is greater than the rate of cell death

Question 30

Stationary phase

Answer 30

Resources become limited, pH alters

- Rate of cell death is equal to the rate of cell division

Question 31

Death phase

Answer 31

Cells begin to die

Question 32

Direct microscope count

Answer 32

Grid on microscope slide (not a viable count because you can’t tell which cells are dead)

Question 33

Spread/ pour plate

Answer 33

Requires serial dilutions and takes 24 hours to get a result

Question 34

Turbidity

Answer 34

The more bacterial cells in a liquid sample, the more turbid and the more light it will absorb
- Not a viable count but can identify log phase