Biology Reference
In-Depth Information
Ph
TAC125 is an interesting model for investigating strategies adopted to
survive at low temperature (
M´digue et al., 2005
). The available genome
sequence, combined with remarkable versatility and fast growth (
Duilio,
Tutino, & Marino, 2004
), makes
Ph
TAC125 an attractive model to study
protein-secretion mechanisms in marine environments, in addition to its
use as a non-conventional host for recombinant production of thermal-
labile and aggregation-prone proteins at low temperature (
Cusano et al.,
2006; Gasser et al., 2008; Parrilli, Duilio, & Tutino, 2008; Parrilli,
Giuliani, Pezzella, et al., 2010; Vigentini, Merico, Tutino, Compagno, &
Marino, 2006
). Actually, low temperatures improve the quality of the prod-
ucts, removing the negative effects of high temperatures on protein folding,
due to the strong temperature dependence of hydrophobic interactions that
mainly drive the aggregation (
Kiefhaber, Rudolph, Kohler, & Buchner,
1991
). The growth of
E. coli
at lower temperatures to minimise aggregation
has not been successful, probably because sub-optimal temperatures act neg-
atively on cell performance (
Gasser et al., 2008
).
The efficiency of the cold-adapted
Ph
TAC125 expression system was
demonstrated by the production of biologically active soluble products,
for example, a yeast
a
-glucosidase, the mature human nerve growth factor
and a cold-adapted lipase (
de Pascale et al., 2008; Parrilli et al., 2008
).
At the genome level, a relatively large number of rRNA genes (nine
rRNA gene clusters) and tRNA genes (106 genes, organised in long runs
of repeated sequences) have been observed in
Ph
TAC125 (
M´digue
et al., 2005
), similar to
Colwellia psychrerythraea
(
Meth´ et al., 2005
) and
Psychromonas ingrahamii
(
Riley et al., 2008
). This finding may be explained
as a response to the limited speed of transcription/translation at low temper-
ature, allowing fast growth in the cold. However, it has recently been spec-
ulated that a high number of rRNA genes may reflect an ecological bacterial
strategy to improve the response to perturbations in nutrient resources
(
Klappenbach, Dunbar, & Schmidt, 2000
). Moreover,
Ph
TAC125 contains
19 genes presumably encoding known RNA-binding proteins or RNA
chaperones. An unexpected feature is the prominent absence of
hns
,an
RNA/nucleoid-associated cold-shock gene found in all
g
-Proteobacteria.
In contrast, the presence of many RNA helicases (three copies of
rhlE
,
and probably a fourth one,
PSHAa0641
, and two copies of
srmB
) instead
of the single one in
E. coli
, suggests that the control of RNA folding and
degradation is important at low temperature (
M´digue et al., 2005
). In fact,
RNA helicases have been found to be over-expressed at low temperature in
many other psychrophilic microorganisms, such as
Methanococcoides burtonii
