Biology Reference
In-Depth Information
no substitution promoting cold adaptation has been found in the
Desulfotalea
psychrophila
genome (
Rabus et al., 2004
).
The proteomes expressed by
Ph
TAC125 at 4 and 18
C were com-
pared (
Piette et al., 2010, 2011
) to identify the cold-acclimation proteins,
that is, those continuously over-expressed at high level at low tempera-
tures, and to highlight the numerous down-regulated cellular functions
(
Piette et al., 2011
). Interestingly, three proteins (Pnp, TypA and Tig,
involved in distinct functions such as degradosome, membrane integrity
and protein folding, respectively) have been identified as CAPs in
Ph
TAC125 (
Piette et al., 2010
) and as CSPs in mesophiles. Moreover, sev-
eral CSP homologues have been reported in other cold-adapted bacteria
(
Bakermans et al., 2007; Bergholz et al., 2009; Kawamoto et al., 2007
),
suggesting striking similarities between CSPs in mesophiles and CAPs in
psychrophiles. In agreement with these results, it has been proposed that
“from an evolutionary point of view, one of the adaptive mechanisms
for growth in the cold is to regulate the cold-shock response, shifting from
a transient expression of CSPs to a continuous synthesis of at least some of
them” (
Piette et al., 2010, 2011
).
The proteomic analyses of
Ph
TAC125 revealed that 30% of the identi-
fied CAPs are directly related to protein synthesis, covering all essential steps,
from transcription (including RNA polymerase RpoB) to translation (i.e.
methionyl-tRNA synthetase MetG that can be connected to the need of
an increased pool of initiation tRNA to promote protein synthesis) and
folding (i.e. the trigger factor—TF—Tig that acts on proteins synthesised
by the ribosome; and PpiD, involved in the folding of outer membrane pro-
teins). The genes
pnp
and
rpsA
also encode components of the degradosome
that regulate transcript lifetimes and two putative proteases (
PSHAa2492
and
PSHAa2260
), identified as CAPs, likely to be involved in the proteolysis
of misfolded proteins (
Piette et al., 2010
). Other identified CAPs are both
components and regulators of the outer membrane architecture (
Piette
et al., 2010
). In particular, the TonB-dependent receptor is indicative of
sensing and exchanges with the external medium, and TypA (involved in
lipopolysaccharides core synthesis) and Pal (a peptidoglycan-associated pro-
tein) are involved in the outer membrane stability and integrity (
Abergel,
Walburger, Chenivesse, & Lazdunski, 2001
).
These results strongly suggest that low temperatures impair protein syn-
thesis and folding, resulting in up-regulation of the associated functions and
indicating that both cellular processes are limiting factors for bacterial devel-
opment in cold environments (
Piette et al., 2010
).
