Deck 4: Dynamics of Prokaryotic Growth

Question 1

You are a microbiologist working for a pharmaceutical company and discover a new metabolite that can serve as a medication. You now must oversee its production. What are some factors you must consider if you need to grow 5,000-liter cultures of bacteria?

Answer 1

In the given case, the goal of microbiologist is to collect more metabolite from the bacterial cultures within a short period of time. So, overexpressing the gene responsible for producing that particular metabolite (by genetic engineering) would be beneficial.
The bacterial metabolites can be the primary or the secondary metabolites, which are synthesized at different phases of cell cycle. The primary metabolites are produced during the log phase (exponential phase), whereas the secondary metabolites are produced during the late log phase and stationary phases.
So, the microbiologist have to consider the phase during which the required metabolite is being produced. As the quantity of media is 5000 liters (L), it is also important to consider the sterilization methods that help to avoid contamination of the microbial cultures. Another concern is, avoiding the final product with endotoxin if the target organism is gram-negative.

Question 2

This figure shows a growth curve plotted on a non-logarithmic, or linear, scale. Compare this with figure 4.6. In both figures, the number of cells increases dramatically during the log or exponential phase. In this phase, the cell number increases more and more rapidly (this effect is more apparent in the accompanying figure). Why should the increase be speeding up?
(In Reference Figure 4.6)

Answer 2

The organisms grow exponentially during the log phase or exponential phase. This phase is called, "balanced growth" because the components required for the cell growth are synthesized at constant rate.
During the log phase of microbial growth curve, the number of cells being produced depend on the number of cells already present, this is because, the cell count doubles with each generation time (exponential growth). Means, if more number of cells are present, the population size also shows a grater "jump."
From the given graph, it can be observed that the population size is lesser at the early log phase, and it showed a greater jump in the population size as the number of cells increased.

Question 3

Most prokaryotes multiply by binary fission. The time required for a population to double in number is the generation time.
Explain why microbial growth refers to populations rather than cell size.

Answer 3

Microbial growth is defined as the growth of the amount of cells in the population. The actual size of the microbial cell is not significant in a given population.

Question 4

If there are 103 cells per ml at the middle of log phase,and the generation time of the cells is 30 minutes,how many cells will there be 2 hours later?

A) 2 × 103
B) 4 × 103
C) 8 × 103
D) 1.6 × 104
E) 1 × 107

Question 5

Describe a detrimental and a beneficial effect of biofilms.

Question 6

High-performance boat manufacturers know that microbes can collect on a boat, ruining its hydrodynamic properties. A boat-manufacturing facility recently hired you to help with this problem because of your microbiology background. What strategies other than routine cleaning would you pursue to come up with a long-term remedy for the problem?

Question 7

Most prokaryotes multiply by binary fission. The time required for a population to double in number is the generation time.
If a bacterium has a generation time of 30 minutes, and you start with 100 cells at time 0, how many cells will you have in 30, 60, 90, and 120 minutes?

Question 8

Compared with their growth in the laboratory, bacteria in nature generally grow

A) more slowly.
B) faster.
C) at the same rate.

Question 9

Define a pure culture.

Question 10

Biofilms have a characteristic architecture with channels through which nutrients and wastes can pass. In nature, prokaryotes often grow in associations with many different species.
Water bowls left out for pets sometimes develop a slimy layer if not washed regularly. What causes the slime?

Question 11

Cells are most sensitive to penicillin during which phase of the growth curve?

A) Lag b) Exponential
C) Stationary
D) Death
E) More than one of these.

Question 12

Explain what occurs during each of the five phases of growth.

Question 13

Biofilms have a characteristic architecture with channels through which nutrients and wastes can pass. In nature, prokaryotes often grow in associations with many different species.
Describe a situation in which the activities of one species benefit another.

Question 14

Lactic acid is a primary metabolite. If a company wants to harvest this compound from a bacterial culture, the cells should be in which growth phase?

A) Lag
B) Exponential
C) Stationary
D) Death
E) More than one of these.

Question 15

Explain how the environment of a colony differs from that of cells growing in a liquid broth.

Question 16

Biofilms have a characteristic architecture with channels through which nutrients and wastes can pass. In nature, prokaryotes often grow in associations with many different species.
Why would bacteria in a biofilm be more resistant to harmful chemicals?

Question 17

coli, a facultative anaerobe, is grown for 24 hours on the same solid medium, but under two different conditions: one aerobic, the other anaerobic. The size of the colonies would be

A) the same under both conditions.
B) larger when grown under aerobic conditions.
C) larger when grown under anaerobic conditions.

Question 18

List the five categories of optimum temperature, and describe a corresponding environment in which a representative might thrive.

Question 19

Only an estimated 1% of prokaryotes can be grown in culture. Agar is used to solidify nutrient-containing broth. The streak-plate method is used to obtain a pure culture. Stock cultures are stored in the refrigerator or frozen.
What properties of agar make it ideal for use in culture media?

Question 20

The generation time of a bacterium was measured at two different temperatures.Which results would be expected of a thermophile?

A) 20 minutes at 10°C; 220 minutes at 37°C
B) 220 minutes at 10°C; 20 minutes at 37°C
C) no growth at 10°C; 20 minutes at 37°C
D) 20 minutes at 45°C; 220 minutes at 65°C
E) 220 minutes at 37°C; 20 minutes at 65°C

Question 21

Why would botulism be a concern with canned foods?

Question 22

Only an estimated 1% of prokaryotes can be grown in culture. Agar is used to solidify nutrient-containing broth. The streak-plate method is used to obtain a pure culture. Stock cultures are stored in the refrigerator or frozen.
To identify the causative agent of a given illness, a pure culture is often needed. How is a streak plate used to obtain a pure culture?

Question 23

Which of the following is false?

A) E. coli grows faster in nutrient broth than in glucose-salts medium.
B) Organisms require nitrogen to make amino acids.
C) Some eukaryotes can fix N2.
D) An organism that grows on ham is osmotolerant.
E) Blood agar is used to detect hemolysis.

Question 24

Explain why O₂ -containing atmospheres kill some microbes.

Question 25

Only an estimated 1% of prokaryotes can be grown in culture. Agar is used to solidify nutrient-containing broth. The streak-plate method is used to obtain a pure culture. Stock cultures are stored in the refrigerator or frozen.
What might be a reason that pathogens can be grown in pure culture more often than environmental organisms?

Question 26

If the pH indicator were left out of MacConkey agar, the medium would be

A) complex.
B) differential.
C) defined.
D) defined and differential.
E) complex and differential.

Question 27

Explain why photoautotrophs are primary producers.

Question 28

When grown in a closed system, a prokaryotic population goes through five distinct phases: lag, exponential or log, stationary, death, and prolonged decline. Cells within a colony may be in any one of the phases, depending on their relative location. Chemostats are used to study uniform populations of growing cells.
Explain the difference between the lag and exponential phases.

Question 29

A soil sample is placed in liquid and the number of bacteria in the sample determined in two ways: (1) colony count and (2) direct microscopic count. How would the results compare?

A) Methods 1 and 2 would give approximately the same results.
B) Many more bacteria would be estimated by method 1.
C) Many more bacteria would be estimated by method 2.
D) Depending on the soil sample, sometimes method 1 would be higher and sometimes method 2 would be higher.

Question 30

Distinguish between a selective medium and a differential medium.

Question 31

When grown in a closed system, a prokaryotic population goes through five distinct phases: lag, exponential or log, stationary, death, and prolonged decline. Cells within a colony may be in any one of the phases, depending on their relative location. Chemostats are used to study uniform populations of growing cells.
Describe how a chemostat keeps cells in a state of continuous growth.

Question 32

The concentration of E.coliin a broth is between 104 and 106 cells per ml. To determine the precise number of living cells in the sample, it would bebest to

A) use a counting chamber.
B) plate out an appropriate dilution of the sample on nutrient agar.
C) determine cell number by using a spectrophotometer.
D) Any of these three methods would besatisfactory.
E) None of these three methods would be satisfactory.

Question 33

If the number of microorganisms in lake water were determined using both a direct microscopic count and a plate count, which method would most likely give a higher number? Why?

Question 34

When grown in a closed system, a prokaryotic population goes through five distinct phases: lag, exponential or log, stationary, death, and prolonged decline. Cells within a colony may be in any one of the phases, depending on their relative location. Chemostats are used to study uniform populations of growing cells.
Why would a compound that prevents bacteria from growing interfere with the function of the antibiotic penicillin?

Question 35

A prokaryotic species can be categorized according to its optimum growth temperature. A species can also be grouped according to its O₂ requirements. Most microbes grow best at a near-neutral pH, although some prefer acidic conditions, and others grow best in alkaline conditions. Halophiles require high-salt conditions.
Clostridium paradoxum grows optimally at 55°C, pH 9.3; it will not grow in the presence of O 2. How should this bacterium be categorized with respect to its temperature, pH, and O₂ requirements?

Question 36

A prokaryotic species can be categorized according to its optimum growth temperature. A species can also be grouped according to its O₂ requirements. Most microbes grow best at a near-neutral pH, although some prefer acidic conditions, and others grow best in alkaline conditions. Halophiles require high-salt conditions.
What is the function of the enzyme catalase?

Question 37

A prokaryotic species can be categorized according to its optimum growth temperature. A species can also be grouped according to its O₂ requirements. Most microbes grow best at a near-neutral pH, although some prefer acidic conditions, and others grow best in alkaline conditions. Halophiles require high-salt conditions.
Why would hydrogen peroxide be an effective disinfectant?

Question 38

Organisms require a source of major and trace elements. Heterotrophs use an organic carbon source, and autotrophs use CO 2. Phototrophs harvest energy from sunlight, and chemotrophs extract energy from chemicals.
To prevent excess phosphate from entering lakes and streams, certain laws govern the amount of phosphorus allowed in laundry and dishwasher detergents. What can happen if phosphorus levels in a lake increase?

Question 39

Organisms require a source of major and trace elements. Heterotrophs use an organic carbon source, and autotrophs use CO 2. Phototrophs harvest energy from sunlight, and chemotrophs extract energy from chemicals.
How would your cells he categorized with respect to their carbon and energy sources?

Question 40

Organisms require a source of major and trace elements. Heterotrophs use an organic carbon source, and autotrophs use CO 2. Phototrophs harvest energy from sunlight, and chemotrophs extract energy from chemicals.
Why would human-made materials (such as many plastics) be degraded only slowly or not at all?

Question 41

Culture media can be complex or chemically defined. Some media contain additional ingredients that make them selective or differential. Appropriate atmospheric conditions must be provided to grow microbes in culture. An enrichment culture increases the relative concentration of an organism growing in a broth.
Distinguish between complex and chemically defined media.

Question 42

Culture media can be complex or chemically defined. Some media contain additional ingredients that make them selective or differential. Appropriate atmospheric conditions must be provided to grow microbes in culture. An enrichment culture increases the relative concentration of an organism growing in a broth.
Describe two methods to create anaerobic conditions.

Question 43

Culture media can be complex or chemically defined. Some media contain additional ingredients that make them selective or differential. Appropriate atmospheric conditions must be provided to grow microbes in culture. An enrichment culture increases the relative concentration of an organism growing in a broth.
Would bacteria that cannot use lactose be able to grow on MacConkey agar?

Question 44

Direct microscopic counts and cell-counting instruments generally do not distinguish between living and dead cells. Plate counts determine the number of cells capable of multiplying; membrane filtration can be used to concentrate the sample. The most probable number estimates cell concentration. Turbidity of a culture can be correlated to cell number. The total weight of a culture can be correlated to the number of cells present. Microbial growth can be detected by the presence of cell products such as acids, gases, and ATP.
Why is an MPN an estimate rather than an accurate number?

Question 45

Direct microscopic counts and cell-counting instruments generally do not distinguish between living and dead cells. Plate counts determine the number of cells capable of multiplying; membrane filtration can be used to concentrate the sample. The most probable number estimates cell concentration. Turbidity of a culture can be correlated to cell number. The total weight of a culture can be correlated to the number of cells present. Microbial growth can be detected by the presence of cell products such as acids, gases, and ATP.
Water that accumulates in dirty bowls and dishes left in the sink often becomes cloudy over time. Besides suspended food particles, what causes the turbidity?