1 / 26

Lactic Acid Bacteria

Lactic Acid Bacteria. Metabolism. Common Energy Metabolism in LAB. Glycolysis (Embden—Meyerhof pathway) --homolactic fermentation The 6-phosphogluconate/phosphoketolase pathway--heterolactic fermentation Significance: fermentation end products relevant to industrial applications. Milk.

sylvana
Télécharger la présentation

Lactic Acid Bacteria

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lactic Acid Bacteria Metabolism

  2. Common Energy Metabolism in LAB • Glycolysis (Embden—Meyerhof pathway) --homolactic fermentation • The 6-phosphogluconate/phosphoketolase pathway--heterolactic fermentation • Significance: fermentation end products relevant to industrial applications

  3. Milk • Lactose • major fermentable sugar, 40–50 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

  4. 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

  5. Sugar Transport by LAB • Several different systems are used by LAB to transport carbohydrates • Depend on species and specific sugar • Phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) • By most mesophilic, homofermentative LAB • Such as lactococci and pediococci for lactose and glucose transport

  6. Sugar Transport by LAB • Symport or ATP-dependent systems • Other LAB • Precursor-product exchange

  7. 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)

  8. Transport hydrolysis systems • Lactose 6-phosphate hydrolyzed by phospho-beta-galactosidase • Exclusively found in G+ • Staphylococcus aureus, L. lactis, Lb. casei, pediococcus spp.

  9. LACTOSE PEP-PTS SYSTEM membrane Medium E-I PEP P-HPr out in pyruvate P-EI HPr LACTOSE P-EIII-lac EII-Lac E-III-lac Lactose-P P-beta-Galactosidase Galactose-6P Glucose

  10. 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

  11. Lactose translocated unmodified Disaccharide hydrolysed by beta–galactosidase (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) Primary and secondary transport systems

  12. 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

  13. lactose galactose lactose galactose Bata-Gal S. thermophilus Lb. bulgaricus Lb. acidophilus Lb. lactis- don’t have the ability to ferment galactose glucose glycolysis

  14. LACTOSE Beta-Gal LACTOSE Gal Glu Gal-1-P Glu-6-P Glu-1-P Glycolysis Lb. helveticus

  15. Symport and ABC Transport Systems in LAB • Driven by ion gradients, and ATP-binding cassette (ABC) systems • Often a bacterium can use a PTS for one sugar and a symport or ABC system for another sugar • Consist a membrane permease with binding sites for both the substrate and a coupling ion, such as H+ or sodium ion (Fig. 2-15)

  16. Symport and ABC Transport Systems in LAB • Such as transport of lactose • Lb. brevis, Lb. delbrueskii, Lb. acidophilus • Galactose • L. lactis • Raffinose • P. pentosaceus • Melibiose • L. lactis • Xylose • Lb. pentosus

  17. Precursor-product Exchange Systems • Widely distributed in LAB • Used to transport fermentation substrates, amino acids, and organic acids • Eletroneutral or electrogenic (Fig. 2-4)

  18. Proton pump • Acid tolerant • Inside: pH ~5.3 • Outside: pH~4.2

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

  20. Protein Metabolism • Cannot assimilate inorganic nitrogen • Rely on amino acids and small peptides • Limited in milk • Depend on proteolysis of casein • Essential for m/o growth • Contribute to flavor and texture development

  21. 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 ? SmallerOligo- peptides Peptidases ? Oligopeptide Transport System Oligopeptides Large Oligo- peptides Proteinase Casein

  22. The Proteolytic System • The cell envelop-associated serine proteianse • Peptide transport system • Oligopeptide transport system • Di-, tri-peptide transport system • Intracellular peptidases

More Related