MODULE 3

Question 1

Distinguish differences of oxidation and reduction.

Answer 1

Reduction and oxidation are chemical processes that involve the transfer of electrons between molecules. Reduction is the process of gaining an electron by a molecule, which is then called “reduced.” Oxidation is the process of losing an electron by a molecule to become oxidized.

Question 2

Explain the differences between autotrophs, heterotrophs, organotrophs and phototrophs.

Answer 2

Autotrophs: CO2 as carbon source
Heterotrophs: organic compounds as carbon source,
Organotrophs: organic compounds as energy source
Phototrophs: light as energy source

Question 3

What are the types of phototrophic microorganisms?

Answer 3

Oxygenic (e.g. Cyanobacteria, algae) or anoxygenic (e.g. purple & green bacteria)

Question 4

A microbiologist describes a bacterium as a chemoheterotrophic, aerotolerant, mesophilic, halophile. Describe the organism’s metabolic features in plain English.

Answer 4

An organism that uses organic carbon compounds as carbon sources, anaerobic but tolerates the presence of oxygen, grows best at moderate temperatures (~30-37°C) and relatively high salt conditions

Question 5

What are major differences between aerobic respiration, anaerobic respiration and fermentation?

Answer 5

Respiration has external terminal electron acceptor: aerobic – oxygen, anaerobic – non-oxygen compounds (e.g. ferric iron, sulfate, sulfur, nitrate, nitrite, etc.). Fermentation doesn’t have an added electron acceptor.
Energetics: aerobic respiration > anaerobic respiration > fermentation

Question 6

Which of the processes in Q5 would obligate aerobes, facultative anaerobes and obligate anaerobes use?

Answer 6

Obligate aerobes: aerobic respiration
Facultative anaerobes: aerobic respiration and often anaerobic respiration
Obligate anaerobes: often anaerobic respiration (note: sometimes can be fermentation)

Question 7

Why are fatty acids a rich source of energy even though no ATP is generated when they are degraded by the beta-oxidation pathway?

Answer 7

Fatty acid chains, which are highly reduced, are obtained from the breakdown of phospholipids or triglycerides. They are oxidized by FADH and NAD+, producing large amounts of FADH2 and NADH. In addition, the smaller carbon products of the β-oxidation pathway can enter the TCA cycle, producing even more FADH2 and NADH. These carriers can donate their electrons to the electron transport chain, thus producing a large amount of ATP.

Question 8

What is the proton motive force, and what is it used for in a cell?

Answer 8

The proton motive force uses an energized cell membrane from electron transport for ATP synthesis via ATPase, transporting some ions and molecules into and out of the cell, flagellar rotation and other energy requiring processes

Question 9

What are chlorophyll and bacteriochlorophyll, and which organisms contain each?

Answer 9

Chlorophylls are used in phototrophs where oxygen is released and can be present in bacteria in addition to eukaryotes. Bacteriochlorophylls are found only in anoxic phototrophs such as purple bacteria and are not present in eukaryotes

Question 10

How can anoxygenic phototrophic microorganisms be of value to the environment even though they do not produce oxygen?

Answer 10

They use CO2 to product organic compounds, CO2 is a greenhouse gas and they help balance out production by other organisms. Also most oxidise H2S which is highly toxic to humans and animals

Question 11

Explain the process of binary fission in bacterial cells.

Answer 11

The process of cell division or growth of prokaryotes. Cell components are replicated then one cell divides into two new cells.

Question 12

Describe the stages of bacterial growth in a batch culture.

Answer 12

Lag, log/exponential, stationary, death

Question 13

Why are microbial generation or doubling times in nature typically longer than those obtained in the laboratory?

Answer 13

Conditions are constant and usually optimal in lab and include a plentiful supply of nutrients, unlike nature. Therefore microbes grow faster with shorter generation times in lab compared with nature.

Question 14

What is the divisome in cell division?

Answer 14

The divisome complex is a series of proteins forming the septum during cell division. It is composed of Fts (filamentous temperature sensitive) proteins

Question 15

What is the role of bactoprenol in cell division?

Answer 15

Bactoprenol is a hydrophobic molecule that carries peptidoglycan precursor building blocks (NAG-NAM with peptide chain) across the cytoplasmic membrane. They interact with transglycosylases to insert them into the spaces produced by autolysins

Question 16

Explain why buffers are commonly used in microbiological media, particularly when growing fermentative bacteria.

Answer 16

Stop fluctuations in pH from the production of acid and alkaline end products of metabolism, especially with fermenters which readily produce organic acids

Question 17

What is the difference between a viable and total count of bacteria?

Answer 17

Total count: all cells, viable count: living cells only

Question 18

What are the advantages and disadvantages of using turbidity as a measure of bacterial growth?

Answer 18

Advantages: rapid, reasonable accurate measure of growth.

Disadvantages: any particulate matter interferes with optical density readings, does
not directly measure cell numbers

Question 19

Why must a standard curve be prepared when using turbidity as a measure of bacterial growth rates?

Answer 19

Turbidity does not measure actual cell numbers. Absorbance is proportional to cell numbers so a standard curve is needed to relate absorbance to numbers.

Question 20

What is the difference between a thermophile and hyperthermophile?

Answer 20

A thermophile grows optimally between 45 and 80ºC, whereas a hyperthermophile grows optimally above 80ºC

Question 21

Why does growing in a salty environment pose a challenge?

Answer 21

A salty environment has higher solute concentration than the cytoplasm of a cell.
Osmotic pressure is placed on the cell and water flows out. A halophile has strategies to overcome this, usually by increasing internal solute levels.

Question 22

How do complex and defined media differ?

Answer 22

Complex media: precise composition is unknown

Defined media: precise composition is known

Question 23

Give an example of a selective and differential medium. What are the components that make it selective and differential?

Answer 23

There are numerous, one is MacConkeys agar: contains bile salts and crystal violet that inhibit growth of gram-positive bacteria. Gram negative bacteria that ferment
lactose produce red/pink colonies while those that do not ferment lactose produce white colonies.

Question 24

One hundred (100) bacterial cells were inoculated into fresh nutrient medium.
There was a lag period of 80 minutes before rapid growth (log or exponential phase) commenced. During log phase, the bacteria had a generation time of 20
minutes. How many cells would there be in the culture 3 hours after inoculation?

Answer 24

N0 = 100, T1 = 180 (min), T0 = 80, g = 20, N1 = ?, n = ?

n = (T1 – T0) / g n = (180 - 80) / 20 = 100/20 = 5

N1 = N0 2n N1 = 100 x 25 = 100 x 32 = 3200 = 3.2 x 103 cells

Question 25

A 100 mL of sterile nutrient broth was inoculated with 5 x 105 bacterial cells. After a 2 hour lag phase the cells then grew exponentially for 4 hours, at which time there
were 3.2 x 107 cells. Calculate the generation time for the bacteria during exponential phase.

Answer 25

N0 = 5 x 105, N1 = 3.2 x 107, T1 = 6 (hours), T0 = 2, g = ?, n = ?

N1 = N0 2n same as: n = (log N1 – log N0) / log 2 = (7.505 – 5.699) / 0.301 = 6

n = (T1 – T0) / g same as: g = (T1 – T0) / n = (6 - 2) / 6, g = 2/3 hr = 40 minutes