AAB Flashcards
acetic acid is also known as ____ acid, or commonly ____.
ethanolic; vinegar
Acetic acid bacteria are involved in producing: (2)
vinegars; kombucha
What is the basic metabolic pathway involved in acetic acid fermentation and what 2 substrates MUST be present?
oxidizing alcohol
require OXYGEN; ALCOHOL
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!
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
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)
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
How can the vinegar making process be accelerated?
More aeration; increase O2 supply
What are 2 examples of bacteria that can generate acetic acid, but are NOT considered AAB? What are they categorized as?
Clostridium, Acetobacterium
Acetogenic
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
4 key genera of AAB:
Acetobacter, Gluconobacter, Gluconacetobacter, Komagataeibacter
Domain, Phylum, Class, Order, Family of AAB?
bacteria proteobacteria alphaproteobacteria rhodospirallales acetobacteraceae
What type of environment are AAB suited for?
high concentrations of sugar/sugar alcohols (flowers, fruit)
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
What types of substrates can gluconobacter use?
D glucose, D sorbitol, glycerol, ethanol
Komagateibacter and acetobacter can use what substrates?
only ethanol
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
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
In periplasmic ethanol oxidation in AAB, no ___ is produced. ___ is the terminal electron acceptor.
CO2
O2
What are the important membrane bound enzymes needed for periplasmic ethanol oxidation in AAB?
alcohol dehydrogenase
aldehyde dehydrogenase
ubiquinone
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?
- 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?
- prevent influx (extracellular polysaccharides, lipopolysaccharides, capsular polysaccharides)
- assimilation (use up generated acetic acid in overoxidation)
- efflux (pump out)
- 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
- prevent denatured proteins from aggregating
- resolubilize aggregated proteins
- 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)
- efflux pumps
- EPS acting as barrier to acid entry
- 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
- break down carbs to ethanol (yeast)
- 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)
