Taxonomy and energy metabolism Lactic Acid Bacteria Taxonomy and energy metabolism

LAB 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 Some other G+ also produce lactic acid (Bacillus, Listeria, Bifidobacterium)

Functions in the food chain Dairy starter culture Vegetable fermentation Alcoholic beverage fermentation (3/4) Meat fermentation Cereal fermentation Probiotics

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

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

Lactic Acid Bacteria: Classification Based on 16S rRNA gene sequence 12 genera (Fig. 2-2) Streptococcus-Lactococcus branch Lactobacillus branch Lactobacillus-Pediococcus branch Oenococcus-Leuconostoc-Weisella branch Carnobacterium-Aerococcus-Enterocccus-Tetragenococcus-Vagococcus The genus Bifidobacterium (G+C55-67%), often considered as LAB, is phylogenetically unrelated and has a unique mode of sugar fermentation Bifidus pathway, fructose-6-phosphate shunt

Lactic Acid Bacteria: Classification Aerococcus, Carnobacterium, Vagococcus, Enterococcus, Tetragenococcus, Leuconostoc, Oenococcus, Weissella, Lactobacillus, Lactococcus, Pediococcus, Streptococcus (Table 2-2)

Energy Metabolism Glucose fermentation TCA cycle Glycolysis (Embden—Meyerhof 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

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

Lactococcus Consists of five phylogenetically-distinct species: L. lactis, L. garviae, L. piscium, L. plantuarum, L. raffinolactis Non-motile, obligate homofermentative, facultative, facultative anaerobes, optimal growth 30C (mesophilic) Cocci, in pairs or short chains

Distinguishing characterisics of dairy Lactococcus Property Lactococcus lactis subsp. lactis L. lactis subsp. cremoris Growth at 40C + - Growth in 4.0% NaCl + - Growth at pH 9.2 + - Growth in 0.1% metgylene blue + - Arginine hydrolysis + - Acid from maltose + - Acid from ribose + -

Streptococcus Non-motile, facultative anaerobes, obligate homofermentative Used to contain four main groups Pyogenic,enterococcus, viridans, lactic Enterococcus and Lactococcus removed from the genus S. thermophilus is the only member in the genus used in food fermentation

S. thermophilus Homolactic Higher optimal growth temp (40-42C) than L. latcis Higher maximum growth temp (52C) Higher thermal tolerance (above 60C) Weakly proteolytic, needs pre-formed amino acids Salt tolerance, bile sensitive, limited metabolic diversity

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+) 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 G+, non-motile, mesophilic, opmimum growth temp 18-25C shape vary (coccoid or rod-like) with growth condition Complex nutrient requirement Obligately heterofermentative Optimal growth pH 6-7 except acidophilic species L. mesenteroides stops around pH 5.4-5.7, so limited effect on lowering pH L. mesenteroides subsp. mesenteroides associated with sauerkraut (pickled cabbage) and dill pickle fermentation, generating CO2 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. 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 Group I: obligate homofermenting species Group II: facultative heterofermenting species Group III: obligate heterofermenting species (Table 2-5)

Lactobacillus Dairy starters: Lb. helveticus, Lb. delbrueckii subsp. bulgaricus Lb. casei, Lb. acidophilus (probiotics) Sausage starter: Lb. plantarum, Lb. sakei subsp. sakei Sourdough starter: Lb. sanfranciscensis, Lb. brevis, etc.