Lactic Acid Bacteria

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Lactic Acid Bacteria

• Carbohydrate and Protein Metabolism

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Cell Wall
Cell Membrane
Cytoplasm
Milk
Amino Acid Transport System
Amino Acids
Amino Acids
Di- and Tri- Peptidases
?
Di/Tri Peptide Transport System
Di/Tri peptides
Di/Tri Peptides
?
Smaller Oligo- peptides
Peptidases
?
Oligopeptide Transport System
Oligopeptides
Large Oligo- peptides
Proteinase
Casein
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LAB proteolytic system

• Fastidious, cannot synthesize some amino acids
• Utilize exogenous N source
• Involves at least a cell wall/membrane associated
  proteinase
• Amino acid, di, tri-peptide and oligopeptide
  transport systems
• Di-, tri-peptidase, oligopeptase

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LAB amino acid metabolism

• 20 basic amino acids
• Amino acids can further be used as building
  blocks
• Or going through metabolism, converting into
  other intermediates such as pyruvate (C3),
  oxaloacetic acid (C4), acetyl (C2)
• The of amino acids vary in casein and some
  insufficient for proper growth, so still rely on
  biosynthesis

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Polysaccharide(pectin, cellulose, starch,
glycogen, Cp)
Carbohydrate metabolism
Enzymes
Enzymes
PEP-PTS system
Disaccharide (C12)
Enzymes
Monosaccharide (C6)
Monosaccharide (C6)
PEP-PTS system
Enzymes
lactate (lactic acid), acetate (acetic acid),
formate, CO2, diacetyl,
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C6 monosaccharide metabolismGlucose, galactose,
fructose, etc.
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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 (C3)
• PEP
• (2) Pyruvate
• 
  
• 
  (2) Lactate

FDP aldolase
Products 2ATP 2Lactate Key enzymes FDP
aldolase Lactate dehydrogenase
(C3)
Lactata dehydrogenase (LDH)
(C3)
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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)
Glucose
facultative anaerobic Anaerobic, aero-tolerant
CO2
Ribulose-5-phosphate
Xylulose-5-phosphate
PK
Glyceralderhyde-3-phosphate
Acetyl-phosphate
Ethanol
Acetaldehyde
Acetate
Pyruvate
Products 2ATP 2 CO2 1 Lactate 1 Acetate Key
enzymes PK LDH (NADH oxidase)
LDH
Lactate
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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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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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Disaccharide Metabolism(Lactose)
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(No Transcript)
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Sugar Transport in LAB
Symport
Antiport
PEP-PTS
Out
In
Energy Source
Proton Motive Force (PMF?pH?? )
Concentration Gradient (?S1?S2 )
PEP
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Transport hydrolysis systems

• The PEP-PTS system
• PEP phosphoenolpyruvate H2CCOPO32-COO-
• PTS phosphotransferase
• Substrate specific system
• EII, EIII induced synthesis by the specific sugar
• EI, HPr soluble components

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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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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
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Proton pump

• Acid tolerant
• Inside pH 5.3
• Outside pH4.2

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Summary

• Glucose fermentation
• Homo- heterolactic fermentation
• Lactose utilization trait unstable
• Strain dependent diversified pathways
• Transport, hydrolysis
• Select for proper starters for specific
  application