Lactic Acid Bacteria Taxonomy and energy metabolism LAB
Lactic Acid Bacteria Taxonomy and energy metabolism
LAB n n n n n Lactic acid bacteria (LAB) - “milk-souring organisms. ” Gram positive Nonsporulating Catalase negative Anaerobic but aerotolerant (facultative anaerobes) Fastidious Low mol% G+C Acid tolerant Strictly fermentative with lactic acid as the major end product during sugar fermentation n Some other G+ also produce lactic acid (Bacillus, Listeria, Bifidobacterium)
Functions in the food chain n n n Dairy starter culture Vegetable fermentation Alcoholic beverage fermentation (3/4) Meat fermentation Cereal fermentation Probiotics
LAB Classification and Identification n Phenotypic/biochemical characters n n n 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
Lactic Acid Bacteria: Classification n Chemotaxonomic markers n Fatty acid composition, constituents of the cell wall etc. n Phylogenetic clusters do not correlate with classification based on phenotypic characters n New tools for classification and identification of LAB n Nucleic acid probing techniques n Partial r. RNA-gene sequencing using PCR (16 S, 23 S r. RNA gene) n Soluble protein patterns
Lactic Acid Bacteria: Classification n Based on 16 S r. RNA gene sequence n 12 genera (Fig. 2 -2) n n Streptococcus-Lactococcus branch n Lactobacillus-Pediococcus branch n Oenococcus-Leuconostoc-Weisella branch n Carnobacterium-Aerococcus-Enterocccus-Tetragenococcus-Vagococcus The genus Bifidobacterium (G+C 55 -67%), often considered as LAB, is phylogenetically unrelated and has a unique mode of sugar fermentation n Bifidus pathway, fructose-6 -phosphate shunt
Lactic Acid Bacteria: Classification n Aerococcus, Carnobacterium, Vagococcus, Enterococcus, Tetragenococcus, Leuconostoc, Oenococcus, Weissella, Lactobacillus, Lactococcus, Pediococcus, Streptococcus (Table 2 -2)
Energy Metabolism n Glucose fermentation n Glycolysis (Embden—Meyerhof pathway) n Pentose phosphate pathway n Four modes with various products (but all contain 5 -C end product or intermediate) n TCA cycle n Oxidative phosphorylation, electron-transport chain n Regenerate NAD+ n Heme
Common Energy Metabolism in LAB n Glycolysis (Embden—Meyerhof pathway) -homolactic fermentation n The 6 -phosphogluconate/phosphoketolase pathway-heterolactic fermentation n Significance: fermentation end products relevant to industrial applications
Lactococcus n Consists of five phylogenetically-distinct species: L. lactis, L. garviae, L. piscium, L. plantuarum, L. raffinolactis n n Non-motile, obligate homofermentative, facultative anaerobes, optimal growth 30 C (mesophilic) Cocci, in pairs or short chains
Distinguishing characterisics of dairy Lactococcus Property Lactococcus lactis subsp. lactis Growth at 40 C + Growth in 4. 0% Na. Cl + Growth at p. H 9. 2 + Growth in 0. 1% metgylene blue + Arginine hydrolysis + Acid from maltose + Acid from ribose + L. lactis subsp. cremoris -
Streptococcus n n Non-motile, facultative anaerobes, obligate homofermentative Used to contain four main groups n Pyogenic, enterococcus, viridans, lactic n Enterococcus and Lactococcus removed n S. thermophilus is the only member in the from the genus used in food fermentation
S. thermophilus n n n Homolactic Higher optimal growth temp (40 -42 C) than L. latcis Higher maximum growth temp (52 C) Higher thermal tolerance (above 60 C) Weakly proteolytic, needs pre-formed amino acids Salt tolerance, bile sensitive, limited metabolic diversity
Pediococccus spp. n n n n n 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+) G+C 34 -44% Surface of plants and fruits Become predominant microflora in fermenting plant materials (silage, sauerkraut, olives, etc. ) Diversified, some grow in beer (spoilage) Also found in cured meat, raw sausages, and marinated fish, and used in biotechnological processing and preservation of foods By Broadbent, USU, NCBI microbial genome
Leuconostoc n n n G+, non-motile, mesophilic, opmimum growth temp 18 -25 C shape vary (coccoid or rod-like) with growth condition Complex nutrient requirement Obligately heterofermentative Optimal growth p. H 6 -7 except acidophilic species n n n L. mesenteroides stops around p. H 5. 4 -5. 7, so limited effect on lowering p. H L. mesenteroides subsp. mesenteroides associated with sauerkraut (pickled cabbage) and dill pickle fermentation, generating CO 2 to reduce the redox potential, producing flavor It also produces exopolysaccharides such as dextran (polymer production) applications in cosmetics, medical, and creation of sephadex gels and beads DOE JGI
Lactobacillus spp. n n n n G+ Non-spore forming Rods or coccobacilli G+C 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
Lactocobacillus n n n Group I: obligate homofermenting species Group II: facultative heterofermenting species Group III: obligate heterofermenting species (Table 2 -5)
Lactobacillus n Dairy starters: Lb. helveticus, Lb. delbrueckii subsp. bulgaricus n n n Lb. casei, Lb. acidophilus (probiotics) Sausage starter: Lb. plantarum, Lb. sakei subsp. sakei Sourdough starter: Lb. sanfranciscensis, Lb. brevis, etc.
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