Ch 6 Microbial Growth

Question 1

Name the physical requirements for microbial growth

Answer 1

1) Temperature
2) pH
3) Osmotic pressure

Question 2

Microorganisms are classified into 3 primary groups on the basis of their preferred range of temperatures

Answer 2

psychrophiles- cold loving
mesophiles- moderate temp loving
thermophiles- heat loving

Question 3

Minimum growth temperature

Answer 3

lowest temp at which the species will grow

Question 4

Optimum growth temperature

Answer 4

temp at which a species grows best

Question 5

Maximum growth temperature

Answer 5

the highest temperature at which growth is possible

Question 6

Psychrotrophs

Answer 6

can grow at 0C
optimum temp= 20-30C
can’t grow above 40C
*food spoilage microorganisms

Question 7

acidophiles

Answer 7

bacteria that are tolerant of acidity

Question 8

Plasmolysis

Answer 8

shrinkage of the cell’s cytoplasm

Question 9

Name the chemical requirements of microbial growth

Answer 9

Carbon= structural backbone of living matter, needed for organic compounds that make up a living cell
Nitrogen= used to form amino group of amino acids of proteins
Sulfur= synthesize sulfur containing amino acids and vitamins (like thiamine and biotin)
Phosphorus= needed for synthesis of nucleic acids and phospholipids of cell membranes

Question 10

Trace Elements

Answer 10

mineral elements that are required in very small amounts

e.g. iron, copper, zinc, molybdenum

Question 11

Obligate Aerobes

Answer 11

• require oxygen to live

- are able to extract more energy from nutrients than anaerobes

Question 12

Facultative Anaerobes

Answer 12

can use oxygen when it’s present but can grow without it (thru fermentation/anaerobic respiration)

Question 13

Obligate Anaerobes

Answer 13

cannot use oxygen for energy yielding rxns (are actually harmed by it)

Question 14

Aerotolerant anaerobes

Answer 14

cannot use oxygen for growth but tolerate it fairly well

Question 15

Microaerophiles

Answer 15

aerobic but only require small amounts of oxygen (grow in oxygen concentrations lower than the air)

Question 16

Toxic forms of Oxygen

Answer 16

1) singlet oxygen- normal molecular oxygen that has been boosted into a higher energy state and is extremely reactive
2) superoxide radicals- aka superoxide anions, are formed during normal respiration of organisms that use O2 as a final electron acceptor to form H2O (form Superoxide dismutase to neutralize them)

Question 17

Organic Growth Factors

Answer 17

essential organic compounds an organism is unable to synthesize on its own, obtained from environment

Question 18

Biofilm

Answer 18

community of microorganisms

Question 19

Culture Medium

Answer 19

nutrient material prepared for growth of microorganisms

Question 20

Inoculum

Answer 20

microbes introduced into culture medium

Question 21

Culture

Answer 21

microbes that grow and multiply on a culture medium

Question 22

Chemically defined medium

Answer 22

medium whose exact chemical composition is known

Question 23

Complex Medium

Answer 23

made up of nutrients, exact chemical composition varies

e.g. nutrient broth and nutrient agar

Question 24

Reducing Media

Answer 24

media that contain ingredients that deplete O2 in culture medium

Question 25

Selective Media

Answer 25

designed to suppress growth of unwanted bacteria and encourage growth of desired microbes

Question 26

Differential Media

Answer 26

make it easier to distinguish colonies

Question 27

Enrichment Culture

Answer 27

provides nutrients and environmental conditions that favor growth of a particular microbe

Question 28

Deep Freezing

Answer 28

process in which a pure culture of microbes is placed in a suspending liquid and quick frozen at temps ranging from -50C to -95C

Question 29

Lyophilization or Freeze Drying

Answer 29

a suspension of microbes is quickly frozen at temps ranging from -54C to -72C and water is removed with a hi vacuum

Question 30

Generation Time

Answer 30

time required for a cell to divide and its population to double

Question 31

Bacterial Growth Curve

Answer 31

graph that shows the growth of cells over time

Question 32

List the phases of a bacterial growth curve

Answer 32

1) lag phase- little/no cell division, synthesis of enzymes and various molecules
2) log phase- cells divide and enter into a period of growth, cellular reproduction is most active
3) stationary phase- growth rate slows, #of microbial deaths balances the # of new cells and population stabilizes
4) death phase- #of deaths exceeds # of new cells formed, population is reduced to tiny fraction

Question 33

Name the methods of measuring microbial growth

Answer 33

1) plate counts
2) serial dilutions
3) pour plates and spread plates
4) filtration
5) most probable number method
6) direct microscopic count

Question 34

Indirect methods of estimating bacterial numbers

Answer 34

• turbidity
• metabolic activity
• dry wt