Bacteria in health
BACTERIA - Defense mechanisms against oxidation
Bacterial Defense against Oxidative Damage
Bacteria need cytochrome c oxidase (oxidase) to survive in
presence of oxygen
- Some
bacteria (one-celled organisms) can use
aerobic respiratory
mechanisms to produce energy from
glucose and
oxygen , some cannotthe deciding factor is whether or not a bacterium contains a large
protein complex cytochrome c oxidase (also called COMPLEX IV or
just oxidase ) in its membrane (referred to as being OX+ or OX-).
- Without cytochrome
c oxidase in its membrane, a bacterium cannot survive in the presence of
oxygen - oxidase is the last
(terminal) enzyme in the respiratory electron transport chain (ETC) required to "harvest"
electrons from
glucose using oxygen for efficient
ATP energy production.
Oxidase catalyzes oxygen's oxidation of the last molecule in
the electron transport chain (ETC) to water - By reducing 1 molecule
of oxygen to 2 molecules of water, oxidase translocates 4 protons across
the membrane to establish a transmembrane potential difference used
by ATP synthase to make ATP).
Oxidase Negative (Ox-)
Oxidase Positive (Ox+)
Enterobacteriae
(E.g. Escherichia, Shigella, Salmonella,
Proteus)
Pseudomonas
VibrioNeisseria
Campylobacter(E.g. C. jejuni
Helicobacter (E.g. H. Pylori)
Legionella
Oxidase+ (OX+) or Oxidase- (OX-)? - an oxidase
test determines whether a bacterium produces cytochrome c oxidase and thus can use
respiratory mechanism to efficiently produce energy
from glucose using
oxygen . Bacteria are OX+ if they contain cytochrome
c oxidase. OX- bacteria can not use aerobic respiratory
metabolism and are unable to live in the presence of
oxygen .
Some bacteria have protective mechanisms against the effects
of oxygen
A bacteria's response to
oxygen (or other oxidizers)
depends on the presence and distribution of certain enzymes
to protect them from damage by oxidation (removal of
electrons ) - these enzymes react with and neutralize
potentially damaging ROS (E.g.
Hydrogen peroxide (H2 O2 Superoxide Radical (O2 .-) )
generated by:
(a) Bacterial cells
in the presence of oxygen
and other oxidizers (E.g.
ozone , chlorine, chlorine dioxide)
Or
(b)
Aerobic cells due to the incomplete reduction
of oxygen
SOD, CAT and GPx detoxify
oxygen radicals that are inevitably generated by living systems in the presence
of O2 . The distribution of these enzymes in cells determines their ability
to exist in the presence of O2
The main 3 cell-protective enzymes
Superoxide dismutase
(SOD) Superoxide dismutase (SOD) enzyme
prevents accumulation of potentially lethal
superoxide(O2 .-)
in aerobes and
Aerotolerant Anaerobes.
All organisms capable of living in the presence ofO 2 necessarily contain
SOD (regardless of whether they utilize
oxygen in their metabolism)
2H+ + 2 O2 - - ==> H2 O2
+O2
Catalase (CAT) Nearly all organisms contain CAT, which catalyzes the
decomposition of hydrogen peroxide (H2 O2 )
to water
2 H2 O2 - ==> 2 H2 O+O2
• Catalase - positive
pathogenic bacteria make catalase to deactivate
peroxide radicals.
Thus allowing these bacteria to survive unharmed within the host.
Srinivasa Rao PS, Yamada Y,
Leung KY (September 2003). "A major catalase (KatB) that is required for resistance
to H2 O2 and phagocyte-mediated killing in Edwardsiella tarda".
Microbiology (Reading, Engl.)149(Pt 9): 2635-2644.
Catalase- POSITIVE BacteriaCatalase -NEGATIVE
Bacteria
Staphylococci
Micrococci
List
eria
Corynebacterium diphtheriae,
Burkholderia cepacia
Nocardia
The Enterobacteriaceae family
( Citrobacter ,
E. coli ,
Enterobacter ,
Klebsiella ,
Shigella ,
Yersinia ,
Proteus ,
Salmonella ,
Serratia ,
Pseudomonas ),
Mycobacterium
tuberculosis,
Legionella pneumophila ,
Campylobacter jejuni ,
Aspergillus
Cryptococcus .
Streptococcus
EnterococcuS spp
• Certain aerotolerant
bacteria (E.g. lactic acid bacteria such as L. Acidophilus)
lack CAT - but
can still decompose H2 O2 by means of
GPx enzymes which reduce
peroxide to H2 O
Glutathione peroxidase (GPx)
(Peroxidase) Reduces peroxide to
H2 O
utilizing the body's major in-house
antioxidant
glutathione
2GSH (Glutathione)
+ H 2 O2 2 O
Obligate
anaerobes usually lack enzymes to remove toxic by-products restricting
them to an oxygen- free
environment.
Obligate
anaerobes lack or have low levels of
SOD, CAT and/or GPx allowing
oxygen radicals
to persist when exposed to oxygen or other oxidizers.
These radicals inactivate other bacterial enzyme systems leading to lethal
oxidations of these bacteria.
Aerobic or
facultative anaerobic bacteria contain
enzymes which can detoxify oxygen
radicals Aerobic or
facultative anaerobic bacteria contain
SOD, CAT or GPx , which
can detoxify oxygen radicals
produced in the presence of oxygen -
converting them to harmless oxygen and water
Group
Superoxide dismutase (SOD)
Catalase
(CAT)
Glutathione
Peroxidase
(GPx)
Obligate aerobes and most
facultative
anaerobes (e.g. Enterics )
+
+
Most aerotolerant anaerobes (e.g.
Streptococci )
+
-
+
Obligate anaerobes (e.g.
Clostridia, Methanogens, Bacteroides )
-
-
