Lactic Acid Bacteria Flashcards
Why one would use anaerobic lactic acid bacteria?
Because it has better vitamin retention and prolonged shelf life
Is LAB gram positive or negative? And do they form spores?
Positive and no spore formation.
Can LAB grow in anaerobic conditions?
Yes but it is also aerotolerant
What are the origins of LAB?
Plant surface and decaying plant material
What are the three ways LAB carries transport inside the cell?
- ATP -> for potassium
- Gradient -> for protons or ions
- PEP-PTS -> for large molecule, sugar which is phosphorylated
Is the conversion of lactose to lactic acid efficient or inefficient?
Inefficient but fast
What are the two fermentation types of LAB?
Homo and heterofermentative
What is another name for the homofermentative pathway?
EMP - Embden-meyerhof pathway
What are the two possible pathways of the EMP and in which conditions do they occur?
- Homolactic fermentation -> if glucose is abundant or under aerobic fermentation
- Mixed acid fermentation -> Sugar is limited or during growth on galactose.
What are the main enzymes responsible for homolactic fermentation and mixed acid fermentation and what is there role?
- Homolactic fermentation -> FDP aldolase which cleaves fructose into 2 glyceraldehyde and LPH (lactate dehydrogenase) which converts a pyruvate into lactate
- 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
What are the product(s) of the homolactic fermentation?
2 ATP
2 Lactate
What are the product(s) of the mixed acid fermentation?
3 ATP
1 Acetate
1 Ethanol
1 Formate
If oxygen is present why can’t the mixed acid fermentation pathway occur?
Because PFL (enzyme) is oxygen sensitive
How is redox reaction restored in the homolactic and mixed acid fermentation?
Homolactic -> Between the Pyruvate and the lactate for
Mixed acid -> Between acetaldehyde and ethanol
What is the other name of the heterofermentative pathway?
Pentose Phosphate pathway
What are the two possible options of the heterofermentative pathway?
Aerobic and Anaerobic conditions
What are the products of anaerobic and aerobic conditions?
Anaerobic -> 1 ATP, CO2, ethanol, lactate
Aerobic -> 2 ATP, CO2, Acetate, lactate
What are the enzymes of anaerobic and aerobic conditions?
Anaerobic -> Phosphoketolase (breaks down sugar) and LDH
Aerobic -> Phosphoketolase (breaks down sugar) and LDH and NADH oxidase which converts oxygen to water.
What is the difference between Phosphoketolase and FDP aldose?
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.
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?
CO2, Acetate and lactate as fructose takes the role of oxygen which is in line with the aerobic conditions.
Why does the citrate metabolism increase pH?
Because it used protons as motion force to create energy
What are the products of the citrate metabolism?
CO2, Formate and Acetate and 1 ATP
Why is Lactate and Ethanol not product of the citrate metabolism?
Because of unbalanced redox reactions.
Why is the citrate metabolism undesired?
Because one of the side products is acetoin which has buttery flavors.
