Lactic Acid Bacteria

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Lactic Acid Bacteria

• Taxonomy and energy metabolism

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LAB

• Lactic acid bacteria (LAB) - milk-souring
  organisms.
• Gram positive, nonsporulating, catalase negative
• Devoid of cytochromes
• Inability to synthesize porphyrin groups, i.e.
  heme.
• Anaerobic but aerotolerant
• Fastidious
• Acid tolerant
• Strictly fermentative with lactic acid as the
  major end product during sugar fermentation

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Functions in the food chain

• Dairy starter culture
• Vegetable fermentation
• Alcoholic beverage fermentation (3/4)
• Meat fermentation
• Cereal fermentation
• Probiotics

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Lactic Acid Bacteria Classification

• Lactococcus, Lactobacillus, Leuconostoc,
  Pediococcus, Streptococcus, Enterococcus
• The genus Bifidobacterium (GC55-67), often
  considered as LAB, is phylogenetically unrelated
  and has a unique mode of sugar fermentation
• Bifidus pathway, fructose-6-phosphate shunt

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Lactic Acid Bacteria Classification

• Aerococcus, Alloiococcus, Carnobacterium,
  Dolosigranulum, Enterococcus, Globicatella,
  Lactobacillus, Lactococcus, Lactosphaera,
  Leuconostoc, Oenococcus, Pediococcus,
  Streptococcus, Tetragenococcus, Vagococcus, and
  Weissella.

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LAB Classification and Identification

• Phenotypic/biochemical characters
• Morphology
• Mode of glucose fermentation
• Growth at different temperatures
• Configuration of the LA produced
• Ability to grow at high salt concentrations
• Acid or alkaline tolerance

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Lactic Acid Bacteria Classification

• Chemotaxonomic markers
• Fatty acid composition, constituents of the cell
  wall etc.
• Phylogenetic clusters do not correlate with
  classification based on phenotypic characters
• New tools for classification and identification
  of LAB
• Nucleic acid probing techniques
• Partial rRNA-gene sequencing using PCR (16S, 23S
  rRNA gene)
• Soluble protein patterns

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Energy Metabolism

• Glucose fermentation
• Glycolysis (EmbdenMeyerhof pathway)
• Pentose phosphate pathway
• Four modes with various products (but all contain
  5-C end product or intermediate)
• TCA cycle
• Oxidative phosphorylation, electron-transport
  chain
• Regenerate NAD
• Heme

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Common Energy Metabolism in LAB

• Glycolysis (EmbdenMeyerhof pathway) --homolactic
  fermentation
• The 6-phosphogluconate/phosphoketolase
  pathway--heterolactic fermentation
• Significance fermentation end products relevant
  to industrial applications

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Pediococccus spp.

• Tetrads via cell division in two perpendicular
  directions in a single plane
• Acid tolerant, cannot synthesize porphyrins,
  lactic acid as major metabolic end product
• Strictly fermentative (homo) facultative
  anaerobic
• Need rich media (N, aa, nicotinic acid,
  pantothenic acid, biotin, some require other Vit)
• Catalase- (some Pseudo)
• GC 34-44
• Surface of plants and fruits
• Become predominant microflora in fermenting plant
  materials (silage, sauerkraut, olives, etc.)
• Diversified, some grow in beer, soy sause
• BeerAlso found in cured meat, raw sausages, and
  marinated fish, and used in biotechnological
  processing and preservation of foods

By Broadbent, USU, NCBI microbial genome
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Leuconostoc spp.

• G, non-motile, shape vary with growth condition
• Complex nutrient requirement
• Facultative heterofermentative anaerobes,
• Optimal growth pH 6-7 except acidophilic species
• L. mesenteroides stops around pH 5.4-5.7
• L. mesenteroides subsp. mesenteroides associated
  with sauerkraut (pickled cabbage) and dill pickle
  fermentation
• It also produces exopolysaccharides such as
  dextran (polymer production) applications in
  cosmetics, medical, and creation of sephadex gels
  and beads

DOE JGI
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Lactobacillus spp.

• G
• Non-spore forming
• Rods or coccobacilli
• GC usually below 50
• Strictly fermentative, aero-tolerant or anaerobic
• Aciduric or acidophilic
• Complex nutritional requirements (carb, aa,
  peptides, FA, salts, nucleic acid derivatives,
  vit)
• Homo or heterofermentative