1. Taxonomy and energy metabolism
Lactic Acid Bacteria
Taxonomy and energy metabolism

2. 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)

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

4. 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

5. 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

6. 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

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

10. 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

14. 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

17. 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

18. 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
Growth in 0.1% metgylene blue
Arginine hydrolysis
Acid from maltose
Acid from ribose

19. 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

20. 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

21. 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

22. 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 , 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

23. 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

24. Lactocobacillus Group I: obligate homofermenting species
Group II: facultative heterofermenting species
Group III: obligate heterofermenting species (Table 2-5)

25. 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.