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Microbiology > VL8: Sruviving in Environment > Flashcards

VL8: Sruviving in Environment Flashcards

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Biology 101 flashcards
1
Q

Name 6 environmental stresses and the ways bacteria use to deal with them

A
  1. Nutrient starvation
    - Scavenging systems
    - Spore formation
  2. Oxidative stress
    - Detoxify
    - Repair
  3. Radiation (e.g. UV light)
    Repair
  4. pH variability
    - Urease activity
    - Escape (chemotaxis)

5- Ionic strength (osmolarity)

  • Pumps
  • Escape
  1. High/low temperature
    - Heat shock response
    - Membrane fluidity
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2
Q

Which medically important bacteria form spores? name 3

A
  • Bacillus anthracis
  • Bacillus cereus (food poisoning)
  • Clostridium tetani tetanus
  • Clostridium botulinum
  • Clostridium perfringens (food poisining and gas gangrene)
  • Clostridium difficile (antibiotic induced diarrhea and pseudomembranous colitis)
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3
Q

Under which conditions do spores form?

A

starvation conditions

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4
Q

Name 6 steps of the sporulation lifecycle

A 
Asymmetric division
Engulfment
Cortex synthesis
Coat formaton
Spore release
Germination
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5
Q

Which molecule is responsible for entry into sporulation?

A

Transcription factor Spo0A
(response regulator, activated by phosphorylation via multi component system with several kinases in response to nutrient limitation, many factors go into regulation)
sigma factors EFEGK control stage specific factors of sporulation sigma factor cascade controlled by Spo0A

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6
Q

What is the SOS regulon? How is it activated?

A

> 30 genes (for DNA repair)
repressed by LexA
DNA damage activates RecA protein -> binds to LexA, LexA autocleaves -> inactive -> repression is lifted

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7
Q

Which kinds of proteins are part of the SOS regulon?

A

rexA: activator of SOS response , homologous recombination

sulA: inhibits cell division until damage is repaired

UmuDC, DinB, PolII: DNA polymerases that can bypass damage

uvrA,B,C,D excision repair, DNA synthesis

lexA Feedback repression of SOS

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8
Q

Why is oxidative stress a problem?

What are the major troublemakers?

A

enzymatic mechanisms and biochem pathways evolved in anaerobic world, avoid reactivity with oxygen

superoxide (O2-) hydrogen peroxide H2O2 +1other
siehe seminar

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9
Q

Name 5 sources of oxidative stress

A
  • Intracellular enzyme autoxidation
  • Environmental redox reactions
  • H2O2 released by competing microbes
  • Phagosomal NADPH oxidase
  • Redox-cycling antibodies
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10
Q

2 proteins that are used as ROS sensors

A

OxyR (contains thiol-disulfide redox switch, seses hydrogen peroxide, activation through oxidation of reactive cysteines -> disulfide bond between 2 cys, conformation change)

SoxR (uses FES cluster to sense superoxide and nitric oxide)

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11
Q

What are some of the targets (protein functions) of OxyR?

A 
H2O2 scavenging
Heme synthesis
FeS cluster assembly
Iron scavenging
Iron import control
Divalent cation import
Disulfide reduction
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12
Q

How is OxyR deactivated?

A

2 major disulfide-reduction systems in e.coli

  1. Glutathione (GSH) together with glutaredoxin proteins
  2. Thioredoxin together with thioredoxin reductase

OxyR response is autoregulated since glutaredoxin 1 is induced by oxidized OxyR

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13
Q

At what temperature grows e.coli?

A

from 21°C to 46°C, maximum growth at 37°C, higher than 42°C -> heat shock response

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14
Q

What kinds of proteins are upregulated in heat shock response?

A

over 40 HSP = heat shock stimulon
chaperones (DnaK DnaJ GrpE…) (insure correct folding of proteins
proteases (Lon, FtsH…) (degrade misfolded proteins, protein aggregates)

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15
Q

How are HSP regulated?

A

cytoplasmic response regulated by sigma32 (rpoH) (most HSP)
periplasmic response regulated by sigmaE (rpoE) (5-10 genes)
both regulons are interconnected (SigmaE rgulations transcription of rpoH and rpoE at high temperatures)

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16
Q

Why are sigma factors important?

A

sigma helps melt DNA to expose transcription start sites

sigma factors alter the cell transcription profile by competing for polymerase cores and determining their promotor specificity

different sigma factors control different sets of genes:
sigma70 Growth/housekeeping 1000 genes
S32 Heat shock 40
SE Extreme heat shock, unfoldet proteins 5

17
Q

What is simga factor partner-switching?

A

Partners before heat shock
Sigma32 mostly chaperones
Sigma70 RNAP

after heat shock:
Sigma 32 mostly RNAP
Sigma70 both chaperones and RNAP
(I don’t really get this…)

Sigma32 gets released during heat shock, more RNApol go to promotors that are regulated by sigma32…

18
Q

How is Sigma32 regulated?

A
  1. rpoH gene has several promotors which need Sigma70 or SigmaE
  2. Translation takes place after the highly structured mRNA is denatured by heat
  3. Sigma32 prot is more stable at high temperatures because other denatured proteins bind more easily to proteases
  4. Chaperones downregulate Sigma32 activity by sequestering them from RNAP
19
Q

Why and how do bacteria have to regulate osmolarity?

A

increase of osmotic pressure -> water efflux, dehydration
solution: increase of osmolytes in cytoplasm (de novo synthesis and active uptake)

decrease of osmotic pressure -> water influx and swelling or lysis
solution: internal solutes are released through membrane channels

20
Q

How is the osmotic stress response regulated?

A
  • osmosensing
  • signal transduction
  • osmoregulation:
  • accumulate or release solutes
  • solutes include inorganic ions (K+) and organic molecules called osmolytes
21
Q

Some examples for solutes that are used to regulate osmolarity?

A

K+
amnino acids (glutamate, proline)
sugars (sucrose, trehalose)
Glycine betaine

Many compatible solutes are effective stabilizers of enzymes. In eubacteria, glycine betaine is the preferred compatible solute and provides the highest level of osmotolerance, which may reflect its favourable interaction with macromolecules

22
Q

What are aquaporines?

A

water channels

bi-directional passive diffusion of water across membranes

23
Q

What is the role of mechanosensitive channels in osmoregulation?

A

function as osmotic safety valves

are closed if cells are in osmotic equilibrium

open when osmotic pressure decreases solutes come in and the pressure changes conformation of channels -> thez open and release solvents

close after equilibrium is reestablished

Microbiology (32 decks)

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