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FDSC442 > 3-Lactic Acid Bacteria (LAB) > Flashcards

3-Lactic Acid Bacteria (LAB) Flashcards

(48 cards)

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1
Q

What are the two classes of lactic acid bactera or the two primary hexose fermentation pathways

A

homofermentative

heterofermentative

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2
Q

LAB are gram ___ and non ____

A

+

non spore forming

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3
Q

T or F : bifidobacterium is a LAB

A

false

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4
Q

___ is the most diverse group of LAB

A

lactobacillus

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5
Q

___ (lactococcus) is commonly used in diary technology

A

Lactococcus lactis

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6
Q

What is the only lactococcus that is commonly used in dairy tech

A

lactococcus lactis

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7
Q

What is the only streptococcus associated with food?

A

S. thermophilus

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8
Q

____, ___ and ___ are each considered tetrad-forming LAB

A

Aerococcus,Pediococcus, and Tetragenococcus are each considered tetrad-forming LAB

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9
Q

What are the LAB with a coccus shape ?

A

leuconostoc
oenococcus
weisella

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10
Q

what is the most acid tolerant genera of the LAB

A

the lactobacillus

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11
Q

T or F : LAB are unable to synthesize many of their essential macromolecules and must obtain them from their environments

A

true

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12
Q

What are the two primary hexose fermentation pathways that are used to classify LAB genera?

A

The Heterofermentative and Homofermentative

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13
Q

what is the pathway used by the LAB to convert glucose if it is a homoermentative LAB

A

glycolytic pathway

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14
Q

what is the pathway used by the LAB to convert glucose if it is a heterofermentative LAB

A

6-PG/PK pathway

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15
Q

What is the role of the PTS (phosphotransferase system)

A

to translocate glucose across the membrane with simultaneous phosphorylation

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16
Q

T or F LAB are unable to ferment disaccharides (such as lactose, maltose, sucrose)

A

false

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17
Q

What are the three categories of LAB metabolism?

A
  1. obligately homofermentative
  2. obligately heterofermentative
  3. faculatively heterofermentative
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18
Q

is LAB a anaerobe or a faculative aerobe?

A

both because it uses oxygen as terminal electron acceptor ( aerobe) but LAB are not able to protect themselves against oxygen

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19
Q

What are the different natural phage defense mechanisms?

A
  1. Absorption Inhibition (shown in figure)
  2. Blocking DNA Penetration
  3. Restriction Enzymes/ Modification Systems
  4. Abortive Infection Mechanisms (bacterial cell traps the phages from emerging)
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20
Q

What are the different artificial phage resistance mechanisms?

Study These Flashcards
A
  1. Antisense RNA
  2. Cloned ORI
  3. Clone in a phage repressor
  4. Phage triggered death
21
Q

How does the Cloned ORI works to give resistance to a bacteria to phages?

Study These Flashcards
A

If the bacteria and the phage as the same ORI there will be a competition and the this will slow the phage

22
Q

How does the clone in a phage repressor works to give resistance to a bacteria to phages?

Study These Flashcards
A

Phage DNA encodes for a repressor of the cell lysis because it wants the bacteria to be full of phages before lysis. If you clone that phage repressor for cell lysis then the cell will never lyse even when it is full of repressor it is a artificial way to make the abortive infection mechanism.

23
Q

How does the phage triggered death works to give resistance to a bacteria to phages?

Study These Flashcards
A

Bacterial suicide genes are placed under the control of a phage inducible promoter

24
Q

What is the optimum temperature of mesophilic LAB

25
What is the optimum temperature of thermophilic LAB
between 48˚C and 58˚C.
26
What are the two other names of lactic acid
milk acid and hydroxypropanoic acid
27
what are the simple carbohydrates that can be metabolized by LAB to form lactic acid ?
1. glucose 2. fructose 3. galactose
28
____ LAB can produce 2 moles of lactate from one mole of glucose
homofermentative
29
____ species can produce one mole of lactate from one mole of glucose, and produce carbon dioxide and acetic acid or ethanol as biproducts
Heterofermentative
30
T or F : the LAB that are heterofermentative can produce carbon dioxide, acetic acid and ethanol as by-products
true
31
What is the definition of the LAB?
are a group of Gram-positive bacteria that produce lactic acid during the fermentation of carbohydrates
32
what is one of the solution of LAB to compete with the competition with other microorganisms?
production of lactic acid
33
what are the shapes of LAB?
rod or cocci
34
____ and ____ are not commonly used in food, and some species of ____ are known foodborne pathogens (E. faecalis)
vagococcus Enterococcus Enterococcus
35
____ and____ are both used as starter for sausage making and silage inoculants
P. acidilactici | P. pentosaceus
36
_____ are extremely salt tolerant (>18% NaCl) and are important in high-salt containing food like soy-sauce
Tetragenococcus
37
___ is a spoilage organism in the beer industry and is responsible for the buttery taste in beer
p. damnosus
38
____ is not used in the food industry but is responsible for greening of cooked meat products
Aerococcus
39
____, ____, and ____ are each coccoid LAB (shape coccus)
Leuconostoc, Oenococcus, and Weisella
40
____ are the most acid-tolerant of the LAB, and will therefore be the final successors of many lactic acid fermentations.
Lactobacilli
41
How does LAB avoid concentration gradients of sugar ?
LAB phosphorylate all in-coming sugars to avoid concentration gradients
42
T or F : glycolysis may lead to heterolactic fermentation (producing alternative end products) under certain conditions
true
43
What are the disaccharides that LAB can ferment?
1. maltose 2. sucrose 3. lactose
44
What can be used as electron acceptor by the heterofermentative LAB?
1. citrate 2. glycerol 3. fructose
45
what is the optimum growth temperature of mesophilic cultures
38 (range from 10 to 48C)
46
what is the optimum growth temperature of thermophilic cultures
between 48 and 58˚C
47
_____ has been shown to have the greatest ability to remove mycotoxins from foods
Lactobacillus rhamnosus
48
what is responsible for the darkening of the sauerkraut?
the oxidation of the ascorbic acid

FDSC442 (19 decks)

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