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Food Microbiology > AAB > Flashcards

AAB Flashcards

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1
Q

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

A

ethanolic; vinegar

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2
Q

Acetic acid bacteria are involved in producing: (2)

A

vinegars; kombucha

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3
Q

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

A

oxidizing alcohol

require OXYGEN; ALCOHOL

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4
Q

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

A

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

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5
Q

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

A

yeast;

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

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6
Q

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

A

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

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7
Q

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

A

acetobacter

ethanol + oxygen -> acetic acid + water

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8
Q

How can the vinegar making process be accelerated?

A

More aeration; increase O2 supply

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9
Q

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

A

Clostridium, Acetobacterium

Acetogenic

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10
Q

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

A
  1. no ethanol intermediate (sugar -> acetic acid)
  2. LOW TOLERANCE to acetic acid (die at high conc)
  3. NOT useful in food production; can even be dangerous
  4. Anaerobic
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11
Q

4 key genera of AAB:

A

Acetobacter, Gluconobacter, Gluconacetobacter, Komagataeibacter

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12
Q

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

A 
bacteria
proteobacteria
alphaproteobacteria
rhodospirallales
acetobacteraceae
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13
Q

What type of environment are AAB suited for?

A

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

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14
Q

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

A

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

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15
Q

What types of substrates can gluconobacter use?

A

D glucose, D sorbitol, glycerol, ethanol

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16
Q

Komagateibacter and acetobacter can use what substrates?

A

only ethanol

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17
Q

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

A

oxidative fermentation
obligate
ethanol/sugar/sugar alcohols
sugar ACIDS

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18
Q

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

A

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

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

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19
Q

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

A

CO2

O2

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20
Q

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

A

alcohol dehydrogenase
aldehyde dehydrogenase
ubiquinone

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21
Q

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

A
  1. alcohol dehydrogenase transfer electrons from ethanol to ubiquinone -> acetaldehyde
  2. aldehyde dehydrogenase transfer electrons from acetaldehyde to ubiquinone -> acetic acid
    (ubiquinone give electrons to O2 (final acceptor) -> water; proton released)
22
Q

What is overoxidation?

A

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

23
Q

How can AAB utilize acetic acid in their metabolism?

A

can oxidize intracellular acetic acid

utilized by ACETYL CO-A SYNTHASE -> acetyl coA

24
Q

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

A

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

25
Q

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

A

False

26
Q

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

A

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

27
Q

What could cause a buttery, spoiled flavor in wine?

A

Acetobacter or gluconacetobacter: oxidize lactic acid to ACETOIN

28
Q

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

A
  1. surface static process

2. submerged process

29
Q

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

A

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

30
Q

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

A

cellulose matrix secreted by bacteria

keeps bacteria afloat next to source of oxygen

31
Q

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: ____.

A

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

32
Q

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

A

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

33
Q

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

A

LIPOPHILIC -> enter membrane easily

ACIDIC -> dissociates (release H+) inside more basic cytoplasm

34
Q

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

A

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

35
Q

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

A
  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
36
Q

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

A

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

37
Q

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

A

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

38
Q

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

A

False; only expressed in presence of ethanol

39
Q

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

A

DnaK-DnaJ-GrpE

fold new proteins, refold denatured proteins, degrade damaged proteins

40
Q

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

A

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

41
Q

AAB that is extremely acid tolerant: ____.

What % acid can it withstand, and what are its uses?

A

Komagateibacter

up to 20%; used in commercial vinegar production

42
Q

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

A
  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)
43
Q

Vinegar is produced from ___ through the process of ___ fermentation

A

usually plant material
(or honey or whey)

aerobic; AAB

44
Q

Vinegar production is a __ step process. Describe it.

A

2

  1. break down carbs to ethanol (yeast)
  2. break down ethanol to acetic acid (AAB)
45
Q

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

A

fungi needed to break down starch first

46
Q

What AAB are most common in natural vinegar fermentation?

A

acetobacter, gluconobacter, gluconacetobacter

47
Q

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

A

cellulose secreted by bacteria cells

creates “raft” to keep cells floating near surface (oxygen)

48
Q

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

A

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

49
Q

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

A

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

50
Q

What is the result of wine that is improperly sealed?

A

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

51
Q

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

A

cleanliness

proper storage

52
Q

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

A

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

Food Microbiology (21 decks)

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