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

3-Lactic Acid Bacteria (LAB) Flashcards

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?

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?

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?

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?

A

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

24
Q

What is the optimum temperature of mesophilic LAB

A

38

25
Q

What is the optimum temperature of thermophilic LAB

A

between 48˚C and 58˚C.

26
Q

What are the two other names of lactic acid

A

milk acid and hydroxypropanoic acid

27
Q

what are the simple carbohydrates that can be metabolized by LAB to form lactic acid ?

A
  1. glucose
  2. fructose
  3. galactose
28
Q

____ LAB can produce 2 moles of lactate from one mole of glucose

A

homofermentative

29
Q

____ species can produce one mole of lactate from one mole of glucose, and produce carbon dioxide and acetic acid or ethanol as biproducts

A

Heterofermentative

30
Q

T or F : the LAB that are heterofermentative can produce carbon dioxide, acetic acid and ethanol as by-products

A

true

31
Q

What is the definition of the LAB?

A

are a group of Gram-positive bacteria that produce lactic acid during the fermentation of carbohydrates

32
Q

what is one of the solution of LAB to compete with the competition with other microorganisms?

A

production of lactic acid

33
Q

what are the shapes of LAB?

A

rod or cocci

34
Q

____ and ____ are not commonly used in food, and some species of ____ are known foodborne pathogens (E. faecalis)

A

vagococcus
Enterococcus
Enterococcus

35
Q

____ and____ are both used as starter for sausage making and silage inoculants

A

P. acidilactici

P. pentosaceus

36
Q

_____ are extremely salt tolerant (>18% NaCl) and are important in high-salt containing food like soy-sauce

A

Tetragenococcus

37
Q

___ is a spoilage organism in the beer industry and is responsible for the buttery taste in beer

A

p. damnosus

38
Q

____ is not used in the food industry but is responsible for greening of cooked meat products

A

Aerococcus

39
Q

____, ____, and ____ are each coccoid LAB (shape coccus)

A

Leuconostoc, Oenococcus, and Weisella

40
Q

____ are the most acid-tolerant of the LAB, and will therefore be the final successors of many lactic acid fermentations.

A

Lactobacilli

41
Q

How does LAB avoid concentration gradients of sugar ?

A

LAB phosphorylate all in-coming sugars to avoid concentration gradients

42
Q

T or F : glycolysis may lead to heterolactic fermentation (producing alternative end products) under certain conditions

A

true

43
Q

What are the disaccharides that LAB can ferment?

A
  1. maltose
  2. sucrose
  3. lactose
44
Q

What can be used as electron acceptor by the heterofermentative LAB?

A
  1. citrate
  2. glycerol
  3. fructose
45
Q

what is the optimum growth temperature of mesophilic cultures

A

38 (range from 10 to 48C)

46
Q

what is the optimum growth temperature of thermophilic cultures

A

between 48 and 58˚C

47
Q

_____ has been shown to have the greatest ability to remove mycotoxins from foods

A

Lactobacillus rhamnosus

48
Q

what is responsible for the darkening of the sauerkraut?

A

the oxidation of the ascorbic acid

FDSC442 (19 decks)

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