microbial energetics. heat shock responses by the gram negative and gram positive bacteria by the protein synthesis mechanism, by those bacteria which are mesophiles in the nature and can survive onlyb at room tempertature.
2. 2
CONTENTSCONTENTS
• Gneral stress for bacteria
• Strategies to fight from the stress
• Examples of stress in bacteria
1. Specific stress responses
2. General stress responses
• Regulation principle of heat shock response in E.coli
• Outline of heat shock reponse
• rpoH mRNA as thermometer
• Heat shock response in E.coli
• The Hsps of E.coli
• Modulation of heat shock response
• Role of σ32,DnaJ/DnaK, and RNAP
• At the level of adaptation
• Regulation
• References
4. 4
1.Physiolochemical and chemical parameters
Pressure, temperature, turgor pressure, irradiation, pH,osmolite/salt
Concentration , oxygen, redox-state.
2.Nutritional Deprivation
Stravation of nutients (carbon, phosphate, nitrogen, amino acids,and
water)
3.Toxic compounds
Toxins, antibiotics, heavy metals, mutagens
4.Interaction with other cells
Hosts cells during infections, high cell density
STRESS FOR BACTERIASTRESS FOR BACTERIA
5. 5
STRATEGIES TO FIGHT THE EFFECT OF STRESSSTRATEGIES TO FIGHT THE EFFECT OF STRESS
1. Elimination of stress factors
Adjustment of intracellular osmolarity
Destruction or secretion of toxins compounds searches for nutritions etc.
2. Repair and damage
DNA repair
Protein repair etc.
2. Escape from the stress situation
Chemotactic movement towards attractants/away from the repellent
Formation of spores and capsules
Morphological adaptations through differntiation
Development of resistance
6. 6
EXAMPLES OF BACTERIAL STRESS RESPONSESEXAMPLES OF BACTERIAL STRESS RESPONSES
1. Specific stress responses
• Heat shock
• Cold shock
• Envelope stress
• Oxidation stress
• Oxygen deprivation
• Amino acid starvation
• Osmotic stress
• Acid stress
• Sodium stress
• SOS response to DNA damage (UV light)
• Metalloregulation between bacterial metals haemostatis and
resistance
8. 8
REGULATION PRINCIPLE OF THE
HEAT SHOCK RESPONSE IN E.coli
REGULATION PRINCIPLE OF THE
HEAT SHOCK RESPONSE IN E.coli
Alternate sigma factor :Sigma 32
Levels of regulation:
Transcription
Translation
Protein activity
Protein stability
9. 9
Outline of heat shock responseOutline of heat shock response
Pics-sciencedaily.com
Conformation change of HSF during
Normal to heat stimulus conditions
10. 10Bakau-heat
Shock response
mRNA
Heat melts the tertiary structure
-shine dalgarno-seq
get free
Translation is facilitated
(gene encoded by
rpoH)-act as a
messe-
-nger.
mRNA TRANSCRIPT
mRNA
11. 11
HEAT SHOCK RESPONSE
IN E.coli
HEAT SHOCK RESPONSE
IN E.coli
• In this organisms there are two heat shock regulons both of
which are positivly regulated at the level of transcription by an
alternate σ- factor. The major one is regulated by σ-32(σ-H)
and the minor one is regulated by σ-24.
• Upon from shift from 30°C to 40°C, E.coli and other bacteria
transiently increases the rate of synthesis of a set of proteins
called heat shock proteins (HSPs).
• Many of the HSPs are required for the cell. Many of these
HSPs are required for the cell growth or survival at more
elevated temperatures (thermtolerance) for
thermophiles.
• Among the induced proteins are DnaJ and DnaK, the RNA
polymerase σ70 subunit lon, ClpAP, FtsH,
LysU(protease). There are nearly 50 heat shock poteins
identified in E.coli.
13. 13
• The σH regulon provides protection against cytoplasmic
thermal stress. The E.coli rpoH locus encodes a 32kD σ factor,
alternativly called σ H or σ32 , which redirects promotor
specificity of RNA polymerase(RNAP). The σ32 protein
regulates the expression of 34 heat shock genes.
• The simple explanation for how heat shock increases
expression of the σ32 regulon ,is that heat shock first cause in
elevation in σ32 levels, which in turn increases expression of
the σ32 target genes.
16. 16
•First temperature upshift from 30°C to 42°C results in
the increased translation of rpoH message.
•Cis- acting mRNA sites within the 5′ region of rpoH
message form temperature -sensitive secondary structures
that sequester the ribosomes binding site.
•At high temperature these secondary structures melt,
thereby enabling more efficient translation of the rpoH
message.
17. 17
• In addition to the increased translation of rpoH message, the
σ32 protein itself become more stable, at least transiently. The
mechanism regulating proteolysis centers on wether σ32
associates with RNA polymerase.
• During growth at 30°C,σ32 can be degraded by several
proteases including FtsH,HsIVU, and ClpAP. However , if σ32
is bound to RNAP, σ32 is protected from degradation.
18. 18
•The cell use DnaK-DnaJ-GrpE chaperone team to interact
with σ32 at low temperature, sequestering σ32 from RNA
polymerase.
•Upon heat shock, there is an increase in the number of
other unfolded proteins or denatured proteins that can be
bind to DnaK/DnaJ molecules available to bind σ 32,
allowing σ32 to bind with RNAP, which protects σ 32
from degradation.
ROLE OF σ32 ,DnaK/DnaJ AND RNAPROLE OF σ32 ,DnaK/DnaJ AND RNAP
Pic-sciencedirect.com
19. 19
AT THE LEVEL OF THE ADAPTATIONAT THE LEVEL OF THE ADAPTATION
• As the cell reaches the adaptation phase following heat shock,
the level of the DnaK and DnaJ rise and can again bind σ32,
redirecting it toward degradation.
• Nevertheless, even through σ 32 degradation resumes,
translation of rpoH remains high at the evaluated temperature
and σ32 continues to accumulate, although at a slower rate.
• In addition of translational and protelytic controls, production
of σ 32 in regulated at the transcriptional level via a feedback
mechanism.
• There are four promoters driving rpoH expression, three of
which are dependent on σ 70, the housekeeping σ factor.
20. 20
• They seemly diverse stresses activate rpoH that appears
responsible is the accumulation of denatured or incomplete
peptides.
• There is a potential alarmone that has been implicated in
signaling exepressions of this global network.
• The σE regulon provide protection against extracytoplasmic
stress.
• The hallmark of the gram- Negative cell is the existence of two
membrane-bound subcellular compartments:the cytoplasm and
the periplasm conditions in each of these compartments differs
makedly.
23. 23
Regulatory mechanismRegulatory mechanism
• Regulated by additional or alternative control channels. These operon is
coding with Hsp10+60 and Hsp70(coded Dnak& groE
operons),respectively contain regulatory inverted repeat (IR=CIRCE) and
trancribed by vegetative factors like σ70 and σ32 factor. Orf act as
represser or HrcA represser.
• The CIRCE normally repressed by the HrcA represser but can be induced
by inactivating. The molecular switch involve chaperone GroE. This is
bind with represser and facilitates folding of HrcA and thereby modulate
represser function.
• The IR functions at the DNA level as a represser binding site and also
controls the half life of the transcripts under non heat conditions.
24. 24
References
• Research article -Buakau, B.1993.regulation in E.coli heat shock
response.Mol. Microbial.
• Albert G. Moat, Jhon W. Foster ,Michael P. Spector ,fourth edition
2004 ,Microbial physiology page no. 597,598,599,600,601.
• Sciencedirect.com
• Sciencedaily.com
• Molbio.com
• Microbiallife.com
• Research papers---
• Research paper-heat shock proteins molecular chaperones,and the stress
reponse-Martin E. feeder dept of organism biology and community on
evolutionary biology, University of Chicago.
• Regulation of heat shock response in bacteria-Gil Segal and Elora Z. Ron
dept. of molecular biology and biotechnology,Tel Aviv University Israel.