AAB Flashcards by Nancy He

acetic acid is also known as ____ acid, or commonly ____.

ethanolic; vinegar

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Acetic acid bacteria are involved in producing: (2)

vinegars; kombucha

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What is the basic metabolic pathway involved in acetic acid fermentation and what 2 substrates MUST be present?

oxidizing alcohol

require OXYGEN; ALCOHOL

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True/False: AAB are considered to be beneficial to wine-making

False: contamination of wine by AAB and exposure to oxygen will turn the wine to vinegar!

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What other organism works with AAB to make kombucha? What is the basic process?

yeast;

2 step fermentation: 1. yeast convert sugar to alcohol; 2. AAB convert alcohol to acetic acid

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True/False: it is possible for some types of bacteria to produce acetic acid WITHOUT oxygen

True; BUT these are NOT considered to be AAB! (diff. pathway)

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What is the bacterial species group that makes most of the world’s vinegar? What is the simplified chemical process?

acetobacter

ethanol + oxygen -> acetic acid + water

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How can the vinegar making process be accelerated?

More aeration; increase O2 supply

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What are 2 examples of bacteria that can generate acetic acid, but are NOT considered AAB? What are they categorized as?

Clostridium, Acetobacterium

Acetogenic

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How do acetogenic bacteria differ from acetic acid bacteria? (4)

no ethanol intermediate (sugar -> acetic acid)
LOW TOLERANCE to acetic acid (die at high conc)
NOT useful in food production; can even be dangerous
Anaerobic

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4 key genera of AAB:

Acetobacter, Gluconobacter, Gluconacetobacter, Komagataeibacter

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Domain, Phylum, Class, Order, Family of AAB?

bacteria
proteobacteria
alphaproteobacteria
rhodospirallales
acetobacteraceae

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What type of environment are AAB suited for?

high concentrations of sugar/sugar alcohols (flowers, fruit)

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True/False: AAB can ONLY use ethanol as a substrate

False: some species can use different sugars as well (depends on species type), or can use accumulated products they make

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What types of substrates can gluconobacter use?

D glucose, D sorbitol, glycerol, ethanol

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Komagateibacter and acetobacter can use what substrates?

only ethanol

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The metabolism of AAB is known as _____ _____. They are classified as ___ aerobes. They consume ________, and create _____.

oxidative fermentation
obligate
ethanol/sugar/sugar alcohols
sugar ACIDS

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Where is ethanol (or sugar alcohols) oxidized in the bacteria? (2) What is the difference?

PERIPLASMIC (cell membrane)
- Partially oxidized; Acetic acid accumulate in MEDIA

CYTOPLASMIC (inside cell)
- Completely oxidized; acetic acid accumulate INSIDE CELL

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In periplasmic ethanol oxidation in AAB, no ___ is produced. ___ is the terminal electron acceptor.

CO2

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What are the important membrane bound enzymes needed for periplasmic ethanol oxidation in AAB?

alcohol dehydrogenase
aldehyde dehydrogenase
ubiquinone

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What is the 2 step process for periplasmic ethanol oxidation in AAB?

alcohol dehydrogenase transfer electrons from ethanol to ubiquinone -> acetaldehyde
aldehyde dehydrogenase transfer electrons from acetaldehyde to ubiquinone -> acetic acid
(ubiquinone give electrons to O2 (final acceptor) -> water; proton released)

What is overoxidation?

complete oxidation of ethanol in cytoplasm, or uptake of acetic acid (intracellular acetic acid) -> enters TCA cycle

How can AAB utilize acetic acid in their metabolism?

can oxidize intracellular acetic acid

utilized by ACETYL CO-A SYNTHASE -> acetyl coA

How does initial ethanol concentration affect AAB growth and resulting product?

1% (lower conc): biphasic growth: first phase is oxidizing ethanol, then oxidizes acetic acid (product)
product: less acetic acid (oxidized)

3% (higher conc): monophasic: too much acetic acid produced, kills bacteria and stops reaction/growth

True/False: all AAB can metabolize acetic acid in the TCA cycle

False

What AAB can use acetic acid in the TCA cycle, and which cannot? Why?

Can: Acetobacter, Gluconacetobacter Cannot: Gluconobacter (missing key enzymes, cannot oxidize organic acids)

What could cause a buttery, spoiled flavor in wine?

Acetobacter or gluconacetobacter: oxidize lactic acid to ACETOIN

What are the 2 methods of carrying out an AAB fermentation?

1. surface static process | 2. submerged process

surface static processes are usually done in a ____ setting. The strains involved are: ____. It can usually reach a concentration of: ___. The bacteria grow in: ____.

home/smale-scale acetobacter 8-9% acetic acid gelatinous film on surface

What is the gelatinous film in AAB fermentations made of, and what purpose does it serve?

cellulose matrix secreted by bacteria | keeps bacteria afloat next to source of oxygen

submerged AAB fermentation can only be found in a ___ setting, and requires: _____. The strains involved are: ___. It can reach concentrations of: ____. The bacteria grow in: ____.

industrial; requires rapid mixing/aeration in bioreactor komagateibacter 15-20% the product itself (mixed in)

True/False: acetic acid is fairly harmless to most bacteria

False; easily diffuses into membranes and dissociates; concentrations as low as 0.5% can kill some bacteria

What properties gives acetic acid its bacteriocidal nature? (2)

LIPOPHILIC -> enter membrane easily | ACIDIC -> dissociates (release H+) inside more basic cytoplasm

What does the entrance of acid into a bacteria cause? What does this trigger? (2)

lowers pH disrupt proton gradient -> can't generate energy, starve messes up protein folding -> misfolded proteins -> interfere with normal cell processes

What are 4 mechanisms that help AAB survive in higher acetic acid concentrations?

1. prevent influx (extracellular polysaccharides, lipopolysaccharides, capsular polysaccharides) 2. assimilation (use up generated acetic acid in overoxidation) 3. efflux (pump out) 4. protect cytoplasmic proteins with general stress proteins

What are molecular chaperones and what roles do they play in AAB (3)? Why are they important?

proteins that act as protection against shock/stress on the molecular level 1. prevent denatured proteins from aggregating 2. resolubilize aggregated proteins 3. degrade seriously damaged proteins ethanol and acetic acid both cause stresses on cell; so AAB need protection to survive in these environments

What is the GroES-Gro-EL system? When is it expressed and what purpose does it serve?

heat-shock protein, expressed when AAB in ethanol or acetic acid HEPTAMER ring structure -> act like cage and prevent denatured protein from aggregating, hold it so it has time to refold

True/False: DnaK-DnaJ-GrpE is expressed when the AAB is in presence of acetic acid

False; only expressed in presence of ethanol

What is an example of a molecular chaperone that performs multiple functions? What functions can it do?

DnaK-DnaJ-GrpE fold new proteins, refold denatured proteins, degrade damaged proteins

How are denatured proteins bound by the DnaJ-DnaK-GrpE system? What is required? How is the protein released?

DnaJ binds protein -> DnaK takes into OPEN cleft DnaJ bind DnaK -> ATP hydrolyzed -> cleft closed (protein now bound tightly) (requires ATP) protein released: GrpE gives ATP to DnaK to release the ADP -> cleft open and protein released

AAB that is extremely acid tolerant: ____. | What % acid can it withstand, and what are its uses?

Komagateibacter | up to 20%; used in commercial vinegar production

What adaptations allow komagateibacter to survive in acidic conditions? (3)

1. efflux pumps 2. EPS acting as barrier to acid entry 3. altered composition of lipid membrane (less area for passive transport of lipophilic molecules; more glycolipids so stronger hydrophobic barrier)

Vinegar is produced from ___ through the process of ___ fermentation

usually plant material (or honey or whey) aerobic; AAB

Vinegar production is a __ step process. Describe it.

2 1. break down carbs to ethanol (yeast) 2. break down ethanol to acetic acid (AAB)

If a starch is used as the base ingredient for vinegar, how does the process differ?

fungi needed to break down starch first

What AAB are most common in natural vinegar fermentation?

acetobacter, gluconobacter, gluconacetobacter

What is the filmy substance found in AAB fermentations and what is the purpose?

cellulose secreted by bacteria cells | creates "raft" to keep cells floating near surface (oxygen)

What are foods/products other than vinegar that use AAB fermentations?

nata de coco (komatageibacter xylinus) kombucha (gluconacetobacter xylinus) vitamin C (komagateibacter xylinus)

True/false: to prevent spoilage caused by AAB in wines, sulfur dioxide is added

FALSE: sulfur dioxide is antibacterial, but has NO EFFECT on AAB

What is the result of wine that is improperly sealed?

aerobic conditions -> AAB can contaminate -> spoilage (low alcohol, off-flavor)

How can AAB spoilage be avoided in wine? (2)

cleanliness | proper storage

True/False: acetic acid is a sign of wine spoilage

true; except in certain products (flanders red ale, lambic beer, etc)