Biology Reference
In-Depth Information
ROS could act as signalling molecules during cell differentiation and cell cycle
progression, and in response to extracellular stimuli (
Sauer, Wartenberg, &
Hescheler, 2001
), they are potentially toxic for cells (
Finkel, 2003
), being
involved in a large number of pathological mechanisms.
Several mechanisms to cope with RNS and ROS have been proposed for
cold-adapted bacteria. They include slightly lower frequency of oxidisable res-
idues in protein sequences, occurrence of specific reductases, presence of
dioxygenases and deletion of RNS- and ROS-producing metabolic pathways
(see
Casanueva et al., 2010
). Interestingly, acyl desaturases (that introduce a dou-
ble bond into fatty-acyl chains, using O
2
as substrate) combine the elimination
of toxic O
2
withtheimprovementofmembranefluidity(
Zhang & Rock,
2008
). Therefore, the augmented capacity in antioxidant defence is likely an
important component of evolutionary adaptation to a cold and O
2
-rich envi-
ronment (
Ayub et al., 2009; Bakermans et al., 2007; Duchaud et al., 2007;
M´digue et al., 2005; Meth´ et al., 2005; Piette et al., 2010; Rabus et al., 2004
).
The cold environment raises the question of how
Ph
TAC125 can cope
with RNS and ROS. We have evidence proving that, in order to prevent
significant damage to cellular structures,
Ph
TAC125 improves the redox
buffering capacity of the cytoplasm, and glutathione synthetase is strongly
up-regulated at low temperature (
Piette et al., 2010
). These adjustments
in antioxidant defences are needed to maintain the steady-state concentra-
tion of ROS and may be important components in evolutionary adaptations
in cold and O
2
-rich environments (
Chen et al., 2008
).
The main adaptive strategy used by
Ph
TAC125, exposed to permanent
oxidative stress, is expected to be increased production of enzymes active
against hydrogen peroxide and superoxide. Surprisingly, in the genome
of
Ph
TAC125, only two genes, encoding an iron superoxide dismutase
(
sodB
;
PSHAa1215
) and a catalase (
katB
, with the possible homologue
PSHAa1737
), have been identified. This catalase has very high similarity
to catalases from other
a
-,
b
- and
g
-Proteobacteria, for example,
Psy-
chrobacter
,
Mannheimia
,
Haemophilus
and
Neisseria
(
M´digue et al., 2005
).
Moreover, while the O
2
-responding OxyR control has been found in
Ph
TAC125, SoxR regulation is absent (
M´digue et al., 2005
).
Proteomic analyses of
Ph
TAC125 reveal that oxidative stress-related
proteins, such as catalase, glutathione reductase and peroxiredoxin (
Piette
et al., 2011
), are repressed at 4
C. However, because
Ph
TAC125 metabo-
lism is stimulated at 18
C, it should be mentioned that, although these pro-
teins would be repressed at 4
C, they would most likely be induced at 18
C
(
Piette et al., 2011
).
