Lactic Acid Bacteria

Question 1

Why one would use anaerobic lactic acid bacteria?

Answer 1

Because it has better vitamin retention and prolonged shelf life

Question 2

Is LAB gram positive or negative? And do they form spores?

Answer 2

Positive and no spore formation.

Question 3

Can LAB grow in anaerobic conditions?

Answer 3

Yes but it is also aerotolerant

Question 4

What are the origins of LAB?

Answer 4

Plant surface and decaying plant material

Question 5

What are the three ways LAB carries transport inside the cell?

Answer 5

1. ATP -> for potassium
2. Gradient -> for protons or ions
3. PEP-PTS -> for large molecule, sugar which is phosphorylated

Question 6

Is the conversion of lactose to lactic acid efficient or inefficient?

Answer 6

Inefficient but fast

Question 7

What are the two fermentation types of LAB?

Answer 7

Homo and heterofermentative

Question 8

What is another name for the homofermentative pathway?

Answer 8

EMP - Embden-meyerhof pathway

Question 9

What are the two possible pathways of the EMP and in which conditions do they occur?

Answer 9

1. Homolactic fermentation -> if glucose is abundant or under aerobic fermentation
2. Mixed acid fermentation -> Sugar is limited or during growth on galactose.

Question 10

What are the main enzymes responsible for homolactic fermentation and mixed acid fermentation and what is there role?

Answer 10

1. Homolactic fermentation -> FDP aldolase which cleaves fructose into 2 glyceraldehyde and LPH (lactate dehydrogenase) which converts a pyruvate into lactate
2. Mixed acid fermentation -> FDP aldolase which cleaves fructose into 2 glyceraldehyde and PFL (pyruvate formate lyase) which converts a pyruvate in an acetyl-CoA and formate

Question 11

What are the product(s) of the homolactic fermentation?

Answer 11

2 ATP
2 Lactate

Question 12

What are the product(s) of the mixed acid fermentation?

Answer 12

3 ATP
1 Acetate
1 Ethanol
1 Formate

Question 13

If oxygen is present why can’t the mixed acid fermentation pathway occur?

Answer 13

Because PFL (enzyme) is oxygen sensitive

Question 14

How is redox reaction restored in the homolactic and mixed acid fermentation?

Answer 14

Homolactic -> Between the Pyruvate and the lactate for
Mixed acid -> Between acetaldehyde and ethanol

Question 15

What is the other name of the heterofermentative pathway?

Answer 15

Pentose Phosphate pathway

Question 16

What are the two possible options of the heterofermentative pathway?

Answer 16

Aerobic and Anaerobic conditions

Question 17

What are the products of anaerobic and aerobic conditions?

Answer 17

Anaerobic -> 1 ATP, CO2, ethanol, lactate
Aerobic -> 2 ATP, CO2, Acetate, lactate

Question 18

What are the enzymes of anaerobic and aerobic conditions?

Answer 18

Anaerobic -> Phosphoketolase (breaks down sugar) and LDH
Aerobic -> Phosphoketolase (breaks down sugar) and LDH and NADH oxidase which converts oxygen to water.

Question 19

What is the difference between Phosphoketolase and FDP aldose?

Answer 19

Phosphoketolase is an enzyme which is involve in the PPP pathway and degrades xylulose.

FDP aldolase is an enzyme which is involved in the EMP pathway and degrades fructose.

Question 20

Leuconostoc mesenteroides can also use fructose as electron acceptor using mannitol dehydrogenase. What are the expected end-products when L. mesenteroides is grown anaerobically on glucose and fructose?

Answer 20

CO2, Acetate and lactate as fructose takes the role of oxygen which is in line with the aerobic conditions.

Question 21

Why does the citrate metabolism increase pH?

Answer 21

Because it used protons as motion force to create energy

Question 22

What are the products of the citrate metabolism?

Answer 22

CO2, Formate and Acetate and 1 ATP

Question 23

Why is Lactate and Ethanol not product of the citrate metabolism?

Answer 23

Because of unbalanced redox reactions.

Question 24

Why is the citrate metabolism undesired?

Answer 24

Because one of the side products is acetoin which has buttery flavors.

Question 25

What does the nitrogen metabolism do and what does it yield?

Answer 25

It degrades proteins and uptake peptides. The nitrogen metabolism is also known as the arginine deiminase pathway and yields 1 ATP, NH3, CO2 and Ornithine (amino acid) and a proton pump.