Section 4: Microbial Growth

Question 1

Temperature requirements

Answer 1

• upper and lower limits of growth
• Psychrophiles: 5-15 degrees C
• Mesophiles: 25-45 degrees C (35-40 in human body)
• Termophiles: 45-70 degrees C

Question 2

O2 requirements

Answer 2

• Obligate aerobes
• Obligate anaerobes
• Facultative anaerobes
• Microaerophiles
• Aerotolerant anaerobes

Question 3

Obligate aerobes

Answer 3

mUST have O2 - aerobic respiration

Question 4

Obligate anaerobes

Answer 4

CANNOT multiply with O2 present, often killed because of presence of O2 (toxic)

Question 5

Facultative anaerobes

Answer 5

grow best WITH O2 (yields most ATP), but can grow without it also.

Question 6

Microaerophiles

Answer 6

requries small amounts of O2, high amounts are inhibitory

Question 7

Aerotolerant anaerobes

Answer 7

indifferent to O2, but does not use/affect energy production

Question 8

Toxic derivatives of O2

Answer 8

• Superoxide: O2-
• Hydrogen peroxide: H2O2 (oxidizing agent but not damaging like a superoxide anion)
• OH-: damaging but transient in cells
• superoxide dismutase: O2- to H2O2 and O2
• catalase: H2O2 to H2O and O2

Question 9

pH

Answer 9

Neutrophiles: 5-8

acidophiles: below 5.5
alkolophile: at / above 8.5

Question 10

water availability

Answer 10

all microbes need H2O for growth, some can survive and multiply in high salt = increasing solute concentration inside cell.

• osmotolerant: TOLERANT of high salt environment = up to 10% (staphylococcus)
• halophiles: REQUIRE high salt, greater than 10%

Question 11

Bacterial Growth - Pure culture

Answer 11

population from a single cell and thus separated from all other species

Question 12

Bacterial Growth - Robert Koch

Answer 12

developed solid agar (used in cooking, from seaweed), contained in petri dishes

Question 13

Binary Fission

Answer 13

after all parts of cell have doubled, then it divides;

• bacterial chromosome is replicated early in life
• cell grows and elongates before division
• DNA is partitioned (mesosome), cell lays down new plasma membrane and cell wall between two daughter genomes
• growth all the way around the cell (cell wall last)

Question 14

generation time

Answer 14

time it takes for a population to double its number

Question 15

Growth Curve (Lab conditions)

Answer 15

1. Lag Phase (latent)
2. Exponential phase (log)
3. Stationary Phase
4. Death Phase

Question 16

Lag Phase (latent)

Answer 16

• Stage 1

- diluted culture, cells “ramp up” = synthesize macromolecules required for division and ATP

Question 17

Exponential Phase (log)

Answer 17

• Stage 2
• cells dividing at a constant rate
• generation time here
• primary metabolites synthesized
• secondary metabolites synthesized (antibiotics)
• growth is balanced with available metabolites

Question 18

Stationary Phase

Answer 18

• Stage 3
• cells have exhausted supply of energy and nutrients
• waste begins to accumulate

Question 19

Death Phase

Answer 19

• Stage 4

- death is exponential (like log), only slower

Question 20

Methods to measure Microbial Growth

Answer 20

1. direct count via microscope or hemacytometer

2. Indirect count via serial dilution