Lactic Acid Bacteria

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Lactic Acid Bacteria

• Taxonomy and energy metabolism (2)

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Lactobacillus spp.

• Group A
• Obligately homofermentative lactobacilli
• 6C to LA by glycolysis (EMP), possess
  fructose-1,6-bisphosphate-aldolase (FDP), but
  lack phosphoketolase (PK)
• Group B
• Facultative heterofermentative
• EMP most, also possess FDP and PK
• Group C
• Obligately heterofermentative

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• Arrangement of the Genus Lactobacillus

Group I obligately homofermentative
Group II facultatively heterofermentative
Group III obligately heterofermentative
Character
- - -
- Lb. acidophilus Lb. delbruckii Lb.
helveticus Lb. salivarius
-
Lb. casei Lb. curvatus Lb.
plantarum Lb. sake
-
Lb. brevis Lb. buchneri Lb. fermentum Lb.
reuteri
Pentose fermentation CO2 from glucose CO2 from
gluconate FDP aldolase present Phosphoketolase
present
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Respiration vs. fermentation

• Respiration
• Glycolysis TCAelectron transport (oxidative
  phosphorylation)
• O2 is final electron receptor
• Glucose (C6) is completely oxidized to CO2
• C6H12O66O2 6CO26H2O38ATP

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Respiration vs. fermentation

• Fermentation
• Glycolysis TCAelectron transport (oxidative
  phosphorylation)
• An organic compound is the final electron
  acceptor
• Glucose (C6) is converted to one or more 1-3
  carbon compounds
• Examples
• C6H12O6 2CH3-CH2OH
  2CO22ATP (ethanol)
• C6H12O6
  2CH3-CHOH-COOH2ATP (LA)
• C6H12O6
  CH3-CHOH-COOHCH3-CH2-OHCO21ATP

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Respiration vs. fermentation

• Some cells can respire and ferment sugars for
  energy, depending on the growth conditions
  (Saccharomyces cerevisiae)
• Some cells can only respire or only ferment
  sugars for energy (LAB)

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Sugar metablism

• Glycolysis
• 6-phosphogluconate/phosphoketolase (6-PF/PK),
  (pentose phosphate pathway, pentose
  phosphooketolase pathway, hexose monophosphate
  shunt)

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C6
C5
FDP aldolase
PK
C2
LDH
C3
2C3
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Homolactic fermentation of Glucose
(Embden-Meyerhof Pathway, GlycolysisLDH)

• Glucose
• G-P
• F-6-P
• F-1,6-P
• Dihydroxyacetone-P
  Glyceraldehyde
• PEP
• (2) Pyruvate
• 
  
• 
  (2) Lactate

FDP aldolase
Products 2ATP 2Lactate Key enzymes FDP
aldolase Lactate dehydrogenase
Lactata dehydrogenase (LDH)
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Mixed Acid Fermentation Alternative end
products for pyruvate
Glucose
FDP aldolase
Dihydroxyacetone-phosphate
Glyceralderhyde-3-phosphate
NAD NADHH
(2) ADP (2) ATP
LDH
(2) ADP (2) ATP
(2)Pyruvate
(2) Lactate
(2)CoA
(2)NADH(2)H
(2)NAD
(2) Formate
PFL
(2) Acetyl-CoA
NADHH NAD
Acetaldehyde
Products 3ATP 2 Formate 1 Ethanol 1 Acetate Key
enzymes FDP aldolase Pyruvate formate lyase (PFL)
Acetyl-phosphate
NADHH NAD
ADP ATP
Ethanol
Acetate
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Heterolactic Fermentation of Glucose (Pentose
Phosphate Pathway)-Aerobic condition
Glucose
NADH oxidase
CO2
Ribulose-5-phosphate
Xylulose-5-phosphate
PK
Glyceralderhyde-3-phosphate
Acetyl-phosphate
Acetate
Pyruvate
Products 2ATP 2 CO2 1 Lactate 1 Acetate Key
enzymes PK LDH NADH oxidase
LDH
Lactate
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Milk

• Lactose
• major fermentable sugar, 4050 g/l
• The glucose moiety of lactose is used faster than
  galactose moiety by lactococci
• Proteins
• Fat
• At the end of the growth phase, less than 0.5 of
  the lactose is used by lactococci
• The fermentation product of the lactococci is
  L()-lactic acid

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Lactose utilization in LAB

• Transport of lactose into cell
• Hydrolysis of lactose
• Metabolism of the monosaccharides
• Efflux of lactic acid and protons from the cell
• Unstable

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Transport hydrolysis systems

• The PEP-PTS system
• Lactose phosphorylated during transport
• Multicomponent group translocation system
• Two cytoplasmic proteins Enz I and HPr
• Two lactose-specific components the
  membrane-located LacE and the soluble
  phosphocarrier LacF (or Enz IIlac and Enz IIIlac)

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Transport hydrolysis systems

• Lactose 6-phosphate hydrolysed by
  phospho-beta-galactosidase
• Exclusively found in G
• Staphylococcus aureus, L. lactis, Lb. casei

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LACTOSE PEP-PTS SYSTEM
membrane
Medium
E-I
PEP
P-HPr
out
in
HPr
P-EI
pyruvate
LACTOSE
P-EIII-lac
EII-Lac
E-III-lac
Lactose-P
P-beta-Galactosidase
Galactose-6P
Glucose
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Pathways for Galactose and Lactose Catabolism
Galactose
Lactose
Galactose
PEP-PTS
Permease
PEP-PTS
Lactose-P
Galactose
Galactose-6P
P-beta-Gal
Gal-1P
Glucose
Tagatose-6P
Glu-1P
Glucose-6P
Glyceraldehyde-3P DHAP
Tagatose 1,6-diP
Glycolysis
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Primary and secondary transport systems

• Lactose translocated unmodified
• Disaccharide hydrolysed by betagalactosidase
  (lacz)
• Primary-involve a sugar transport ATPase
• Agrobacterium radiobacter, Strep. mutans
• Secondary-couples with ions or other solutes
• L. lactis ATCC 7962 (proton), E.coli (LacY)

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Secondary transport systems

• Secondary-couples with ions or other solutes
• L. lactis ATCC 7962 (proton-coupled), E.coli
  (LacY)
• LacS in Strep. thermophilus
• Proton symport or lactose-galactose antiporter

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lactose
galactose
lactose
galactose
Bata-Gal
S. thermophilus Lb. bulgaricus Lb.
acidophilus Lb. lactis- dont have the ability
to ferment galactose
glucose
glycolysis
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LACTOSE
Beta-Gal
LACTOSE
Gal
Glu
Gal-1-P
Glu-6-P
Glu-1-P
Glycolysis
Lb. helveticus