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BACTERIAL
RESPONSE
TO
OXIDATIVE
STRESS
INTRODUCTION
Oxidative stress (OS) is the term applied when
oxidants outnumber antioxidants.
 The reaction between ferrous (iron), and oxygen
results in the formation of harmful superoxide
and hydroxyl radicals, which affect all
macromolecules.
 Reactive oxygen species (ROS) represent the
collection of number of molecules and free
radicals derived from molecular oxygen in
addition, there is another class of free radicals
that is RNS.


Excessive generation of ROS, which damages
cells, tissues and organs. Highly reactive
radicals cause the oxidative damage of different
macromolecules proteins, DNA, and lipids.

The sources of ROS are as follows: smoking,
herbicides, pesticides, fried foods as well as
industrial contaminants that are widespread in
soils and on the surfaces of plants.
STRESS RESPONSE
 A global
response induces an adaptive metabolism
including
• ROS elimination,
• The bypass of injured pathways,
• Reparation of oxidative damages.
• Maintenance of reducing power.
 Living organisms have to build up mechanisms to
protect themselves against oxidative stress, with
enzymes such as catalase and superoxide
dismutase.
 The toxic forms of oxygen include Hydroxyl
radical, Superoxide radical & Hydrogen peroxide.
 There
does not exist any mechanism to detoxify
hydroxyl radicals formed by H2O2.
 The enzyme SOD converts superoxide to H2O2
and O2 catalase converts and H2O2 to water and
oxygen.
 The redox cycling reagents like methyl viologen
accepts an electron from NADPH or NADH
which lead to synthesis of proteins used in
protection.
 Examples of enzymes induced in E.coli are Mn2
superoxide dismutase , endonuclease IV.
GENETIC FACTORS
 Bacterial
genetic responses to oxidative stress are
controlled by two major transcriptional factors
viz.,OxyR and SoxRS.
 Peroxide and superoxide are the two major active
oxygen species.
 PEROXIDE RESPONSE
Oxy R is a homotetramer , its activated form has
an disulfide bond between two cysteine residues
 OxyR is a transcriptional activator for genes like
katG.
 helps in reorganization of metabolism under
stress conditions.
SUPEROXIDE RESPONSE
 Sox R is an iron sulfide protein.
 Activated SoxR then activates SoxS protein which
activates transcription of target genes.
 Examples of activated genes are sodA (codes for Mn2
superoxide dismutase),nfo(codes for endonuclease IV).
 THIOREDOXINS AND GLUTAREDOXINS PLAY AN
ROLE IN REDUCING DISULFIDE BONDS IN OxyR
AND OTHER PROTEINS IN CYTOPLASM
 They reduce the disulfide bonds in proteins to sulfhydryl
groups.
 They have pairs of cysteine residues separated by two
amino acids.
 Reduced thioredoxin is regenerated by NADPH and
reduced glutaredoxin by reduced glutathione

DEFENCE MECHANISMS
 Defence
mechanism either keep the
concentration of the O2-derived radicals at
acceptable levels or repaired oxidative damages.
 Iron plays a significant role in biology.
 Some
examples of bacterial defences are: 1)Metal
chelators- e.g.,metallothionine,ferretin.
2)Low molecular weight compounds and antioxidant
enzymes e.g., SOD, catalase.
3) DNA repair systems protein repair system lipid
repair system e.g., methionine , sulfoxide reductase.
CYTOCHROME OXIDASE BD
 Cytochrome
bd oxygen reductase from
Escherichia coli has three hemes, b558,b595 and
d.
 The enzyme is found only in prokaryotes and
may serve other important physiological
functions.
 The protective role of cytochrome bd against
H2O2 stress is corroborated by the information
that the E.coli mutants unable to synthesize the
bd oxidase are sensitive to H2O2 and that
expression of cytochrome bd increases in the
presence of external H2O2.
Some other defences of bacteria against
oxidative stress
1) In E.coli BtuE peroxidase protects the bacterium against
oxidative stress that is generated by tellurite and by other
reactive oxygen species.
 Cells overexpressing BtuE exhibited increased resistance
to compounds whose toxicity involves ROS generation.
2)Simultaneous expression of NOD2 and DUOX-2 was
found to result in co-operative protection against bacterial
cyto-invasion.

ROS production and protein & lipid modification induced
by ROS have been seen in Crohn's disease.
3)NADPH homeostasis plays an important role in proper
execution of soxRS response .

NADPH oxidation by ferrodoxin or by the NADPH
diaphorase
led
to
significant
soxS
accumulation
in
anaerobiosis, and no superoxide forms.
4) The tRNA upregulation increases the survival of E.coli under
harsh oxidative stress.

At a sub -MIC concentration of ciprofloxacin , tRNA
augmented bacteria grew significantly faster than control
cells, thereby providing the bacteria
with elevated tRNA
concentrations a survival advantage in presence of antibiotic.
CONCLUSION
Oxidative stress (OS) is the term applied when oxidants
outnumber antioxidants.
 Reactive oxygen species (ROS), are hydroxyl radicals
(OH) , hydrogen peroxide (H2O2), superoxide radicals.
 Regulation of oxidation response in bacteria involving
OxyR and SoxRS regulons.
 Heavy metal pollution is a serious problem worldwide
there is a growing need to elucidate its toxic effects in a
sensitive microorganism.

Excessive ROS formation leads to tissue destruction
ultimately resulting in inflammatory disorders. Thus the
study can be helpful in treatment of diseases in medical
field.

 Recent
work has demonstrated that ROS have a
role in cell signalling, including; apoptosis; gene
expression; and the activation of cell signalling
cascades.
 It
should be noted that ROS can serve as both
intra- and intercellular messengers.
REFERENCES

Adriana R. Krapp , Maria Victoria Humbert , and Nestor
carrillo;The soxRS response of Escherichia coli can be
induced in the absence of oxidative stress and oxygen
modulation of NAdph content;2010; SGM journals.

Felipe A. Arenas, Paulo C. Covarrubias, Juan M.
SAndoval, Jose M. Perez-donoso , James A. Imlay,
Claudio C . Vasquez;The Escherichia coli BtuE protein
functions as a resistance determinant against reactive
oxygen species;volume 6 ,2011;PLOS ONE.

Jiayong Zhong, Chuanle Xiao ,Wei Gu, Gaofei Du ,
Xuesong Sun , Qing-Yu he , Gong Zhang;Transfer Rnas
mediate the rapid adaptation of Escherichia coli to
oxidative stress ;2015; PLOS genetics.

Simone lipinski, Andreas Till, Christian Sina , Alexander
Arit, Helmut Grasberger, Stefan Schreiber and Philip
Rosenstiel; DUOX2-derived reactive oxygen species are
effectors
of
NOD2-mediated
antibacterial
responses;2009; Journal of cell science.

Vitaliy B. borisov , Elena forte, Albert Davletshin ,
Daniela Mastronicola, Paolo Sarti, Alessandro
Giuffre;Cytochrome bd oxidase r from Escherichia Coli
displays Hgh Catalase activity:An additional defense
against oxidative stress;2013;Elsevier B.V.