Biology Reference
In-Depth Information
TF is transiently expressed in mesophilic bacteria but continuously over-
expressed in psychrophiles to achieve cold adaptation, rescuing the chaper-
one function at low temperatures (
Piette et al., 2010, 2011
).
Either PPiases or TF act as potential CAPs in the proteome of most cold-
adapted microorganisms analysed so far (
Goodchild et al., 2005, 2004;
Kawamoto et al., 2007; Qiu et al., 2006; Suzuki, Haruki, Takano,
Morikawa, & Kanaya, 2004; Ting et al., 2010
), suggesting that the constraint
imposed by protein folding at low temperature and the cellular responses are
common traits in most psychrophiles (
Piette et al., 2010
). In contrast, an
almost inverse regulation was found in
P. arcticus
where GroEL/ES
chaperonins and repression of TF are up-regulated under cold conditions
(
Bergholz et al., 2009; Zheng et al., 2007
). Increased synthesis of
chaperonins has also been reported in
S. alaskensis
(
Ting et al., 2010
)
possessing two sets of
dnaK-dnaJ-grpE
gene clusters; proteomic analysis sug-
gests that one of these sets functions as a low-temperature chaperone system
whereas the other functions at higher temperatures (
Ting et al., 2010
).
At low temperature, in accordance with reduced biomass, almost half of
the down-regulated proteins are involved in general bacterial metabolism.
Most of these proteins are involved in oxidative metabolism, including gly-
colysis, the pentose phosphate pathway, the Kreb's cycle and the electron
chain transporters (
Piette et al., 2011; Wilmes et al., 2011
).
The
Ph
TAC125 genome contains genes putatively involved in NO
metabolism, such as NO reductase,
PSHAa2417
,andNO
2
reductase,
PSHAa1477
(
M´digue et al., 2005
). In this context, the presence of multiple
genes in distinct positions on chromosome I encoding three TrHbs (annotated
as
PSHAa0030
,
PSHAa0458
,
PSHAa2217
)andaFHb
PSHAa2880
)
(
Giordano et al., 2007; M´digue et al., 2005
) may be pivotal for cell protection
(see
Section 6
).
5.3. Excess of O
2
and metabolic constraints
Gases (e.g. O
2
) and radicals (e.g. NO) are highly soluble and stable at
low temperature with visible consequences in genome annotations in
cold-adapted bacteria, having developed responses to strong oxidative stress
(see
Casanueva et al., 2010
).
The apparent benefits of easier O
2
supply are contrasted by the adverse
effects of low temperature on (macro)molecular functions and on the
increased production of RNS and reactive oxygen species (ROS)
(
Casanueva et al., 2010; D'Amico et al., 2006
). In fact, although RNS and
