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MICR3330 > 5 - Bacterial Endospores > Flashcards

5 - Bacterial Endospores Flashcards

1
Q

Endospores

A
  • Resistant, dormant spores formed in some genera of bacteria
  • Resistant to chemicals, temperature, and radiation
  • Confer resistance, survival and dormancy to host bacteria
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2
Q

Which bacteria form endospores

A
  • Only members of the low GC subdivision of gram +ves
  • Make a single endospore per cell that later germinates to form a single cell
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3
Q

Genera of endospore forming bacteria

A
  • Bacillus (rods, aerobic)
  • Clostridium (rods, anaerobic)
  • Sporosarcina (cocci, aerobic)
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4
Q

Swollen sporangium

A

Spore is wider than the width of the vegetative cell

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5
Q

Different locations of endospores

A
  • Terminal
  • Subterminal
  • Central
  • Each location can also be swollen
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6
Q

Human significance of endospores

A
  • Set the sterilisation standard
  • Medical importance
  • Bioterrorism
  • Developmental biology
  • Pest control in agriculture
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7
Q

How did endospores set the sterilisation standard

A
  • Endospores survive hours of boiling, and most chemical disinfectants
  • Sterilisation processes must kill endospores (autoclave)
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8
Q

Medical importance of endospores

A
  • Several spore-forming species are dangerous pathogens (e.g. tetanus)
  • Spores provide a source of contamination & infection
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9
Q

Endospore bioterrorism

A

Use of Bacillus anthracis as a bioterror weapon is based on production and spread of its endospores

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10
Q

Endospore developmental biology

A

increased understanding of differentiation in bacteria

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11
Q

Endospore pest control

A
  • Bacillus thuringiensis is
    an insect biopesticide
  • Produces a toxic protein
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12
Q

What triggers sporulation

A
  • Bacterial response to unfavourable conditions
  • Occurs in stationary phase
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13
Q

unfavourable conditions that can trigger sporulation

A
  • Absence of nutrients (C, N, P)
  • Desiccation (removal of moisture)
  • Presence of toxins or antibiotics
  • Overcrowding
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14
Q

Structure enclosing
cytoplasm in vegetative cells vs endospores

A
  • Vegetative cells: Typical G+ve cell (CW, PM)
  • Endospores: Complex of layers
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15
Q

Microscopic appearance in vegetative cells vs endospores

A
  • Vegetative cells: non refractile
  • Endospores: refractile
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16
Q

Enzymatic activity in vegetative cells vs endospores

A
  • Vegetative cells: High
  • Endospores: Absent
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17
Q

Metabolism in vegetative cells vs endospores

A
  • Vegetative cells: High
  • Endospores: Absent
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18
Q

Macromolecular synthesis in vegetative cells vs endospores

A
  • Vegetative cells: Present
  • Endospores: Absent
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19
Q

Resistance (heat, radiation, chemical) in vegetative cells vs endospores

A
  • Vegetative cells: Low
  • Endospores: High
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20
Q

Sensitivity to lysozyme in vegetative cells vs endospores

A
  • Vegetative cells: Sensitive
  • Endospores: Resistant
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21
Q

Sustainability in vegetative cells vs endospores

A
  • Vegetative cells: Easy to stain
  • Endospores: Special methods needed
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22
Q

Cytoplasmic pH in vegetative cells vs endospores

A
  • Vegetative cells: ~7
  • Endospores: ~5.5-6
23
Q

Endospore Exosporium

A
  • Outermost layer in SOME species
  • Thin glycoprotein layer outside spore coast
  • Hair like projections and a basal layer
  • Mediates environmental inerations (e.g. adhesion)
24
Q

Endospore Spore coat

A
  • Keratin-like protein layers rich in S-S bonds
  • HIghly impermeable
  • Provides resistance to chemicals (e.g. lysozyme)
25
Q

Four layers of spore coat

A

Basement, inner, outer, crust

26
Q

Endospore cortex

A
  • Peptidoglycan with reduced cross linking of NAM residues because cortex PG if modified
27
Q

Function of endospore cortex

A

Loosely cross-linked flexible cortex may allow spore envelope to expand and contract in response to humidity change

28
Q

Endospore core wall

A
  • Typical cell wall (but no teichoic acids)
  • Provides osmotic stability
    at spore germination
  • Acts as a primer for regrowth of the vegetative cell wall
29
Q

Endospore inner membrane

A

Like PM is a good permeability barrier

30
Q

Endospore core

A
  • Cell components typical of
    bacterial cell (nucleoid DNA,
    ribosomes, rRNA, tRNA, etc)
  • Components unique to spore
31
Q

Contents of endospore core

A
  • Calcium dipicolinate
  • Water content
  • Small acid soluble DNA binding proteins (SASPs)
  • Phosphoglyceric acid
32
Q

Calcium dipicolinate

A
  • Replaces water
  • Absent in normal vegetative cells
  • Inserts between DNA bases, helps stabilise the spore DNA and protect it
33
Q

Water content

A

Low water and lower pH contribute to dormancy and spore survival

34
Q

Small acid soluble DNA binding proteins (SASPs)

A
  • High concentrations
  • Alter 3D DNA structure fro, B to A form which is less susceptible to UV damage
  • Provide amino acids, carbon and energy for biosynthesis
35
Q

Phosphoglyceric acid

A

Source of P for ATP generation on germination

36
Q

Endospore ATP, mRNA, amino acids and protein synthesis enzymes

A
  • Absent or insignificant in endospores
  • Reflects lack of metabolism
37
Q

Seven stages of endospore formation

A
  1. Axial filament formation
  2. Septum formation
  3. Engulfment of forespore
  4. Cortex formation
  5. Coat synthesis
  6. Maturation
  7. M0ther cell lyses and releases endospore
38
Q

Is endospore cell division symmetrical or asymmetrical

A

Asymmetrical

39
Q

Coat synthesis

A

a second impermeable
protective layer forms outside the cortex, and the exosporium forms

40
Q

Axial filament formation

A

DNA has replicated but not separated

41
Q

How long does endospore formation take

A

8 hours

42
Q

Genes that control Endospore formation

A
  • spo genes (control of overall sporulation process)
  • ssp genes (act inside the endospore, encode SASPs)
  • cot genes (act in mother cell, encode spore coat proteins)
43
Q

How have mutation studies elucidated the processes
controlling endospore formation

A

mutations in particular genes arrest process at different structural and functional stages

44
Q

what systems control sporulation

A

Controlled by phosphorelay in a two component regulatory system and alternate sigma factors

45
Q

What senses unfavourable environmental conditions (e.g. nutrient depletion)

A

Sensor kinase proteins such as KinA

46
Q

KinA

A
  • KinA autophosphorylates
  • Phosphoryl group then transferred between
    Spo proteins in a phosphorelay
  • Eventually Spo0A is phosphorylated
47
Q

spo0A

A
  • Master regulator
  • Response regulator protein
  • Phosphorylated Spo0A represses genes required for vegetative growth, and activates genes required for
    sporulation
48
Q

Sigma factor genes

A
  • σF (early sporulation gene transcription) and σG (Late sporulation gene transcription)
  • Transcribe genes needed in the forespore or the mother cell
49
Q

Two component regulatory system of control of endospore formation

A

System with with a sensor protein (KinA) and a response regulator protein (spo0A)

50
Q

3 stages involved in breaking endospore dormancy

A
  1. Activation
  2. Germination
  3. Outgrowth
51
Q

Activation

A
  • Prepares spores for germination
  • Requires some form of shock
  • Involves damage to spore coat (germination may not occur unless there is coat damage)
  • Reversible if a germination agent is absent
52
Q

Germination

A
  • The dormant endospore starts metabolic activity
  • Triggered by water and a germination agent (e.g. sugar or amino acid) penetrating the exosporium and coat
  • Germination agent interacts with inner membrane receptors, signal sent to activate germination
53
Q

Germination events

A
  1. Cations secreted
  2. Spore swells (H2O replaces Ca-DPA)
  3. Cortex peptidoglycan is degraded by lytic enzymes (core rehydrates)
  4. Initiation of metabolic activity
  5. Degradation of coat by proteases
  6. Loss of heat resistance
  7. SASPs degraded (supplying amino acids, DNA repaired)
  8. ATP generated from 3 phosphoglycerate
54
Q

Outgrowth

A
  • Cell components are made in the core (SASPs act as carbon and energy source - makes proteins, RNA, DNA)
  • Protoplast emerges
  • Vegetative growth is resumed

MICR3330 (29 decks)

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