Biology Reference
In-Depth Information
TrHbs belonging to the three groups may coexist in some bacteria,
suggesting distinct functions. These globins have been hypothesised to store
ligands and/or substrates, to facilitate NO detoxification, to sense O
2
/NO,
to display (pseudo)enzymatic activities and to deliver O
2
under hypoxic
conditions (
Vinogradov &Moens, 2008; Wittenberg et al., 2002
). The high
O
2
affinity suggests that some TrHbs may function as O
2
scavengers rather
than O
2
transporters (
Ouellet et al., 2003; Wittenberg et al., 2002
).
5. THE ANTARCTIC MARINE BACTERIUM
PSEUDOALTEROMONAS HALOPLANKTIS TAC125:
A CASE STUDY
5.1. General aspects
Despite the fact that the Antarctic marine environment is characterised by
permanent low temperatures, the surface water and the sea-ice zones host
a surprisingly high level of microbial activity.
A typical representative of
g
-Proteobacteria found in the Antarctic is the
marine cold-adapted psychrophile
P. haloplanktis
TAC125 (
Ph
TAC125), a
Gram-negative bacterium, isolated in Antarctic coastal sea water in
the vicinity of the French station Dumont d'Urville, Terre Ad´lie
(66
40
0
S; 140
01
0
E). As in many marine
g
-Proteobacteria, its genome is
made up of two chromosomes (
M
´
digue et al., 2005
). This strain thrives
between
2
C and 4
C, but is also able to survive long-term frozen con-
ditions when entrapped in the winter sea ice.
Ph
TAC125 can grow in a wide
temperature range (4-25
C) (
Fig. 8.3
A) and achieve very high cell density
even under uncontrolled laboratory conditions (
Fig. 8.3
B). In a marine
broth,
Ph
TAC125 displays a doubling time of about 4 h at 4
C and 5 h
15 min at 0
C. At higher temperatures, the bacterium divides actively
and the generation time decreases moderately (e.g. 1 h 40 min at 18
C),
with increase in the biomass produced at the stationary phase (
Piette
et al., 2011
). In contrast, higher temperatures cause a drastic reduction in
cell density at the stationary phase, suggesting that the heat-induced stress
affects the growth (
Piette et al., 2011
).
The doubling time of
Ph
TAC125 at 16
C is approximately 2 h, almost
three times faster than that of
E. coli
under similar growth conditions (
Piette
et al., 2010
). Consistent with the high growth rate, at room temperature,
Ph
TAC125 shows a very efficient chemotactic response, 10 times faster than
that of
E. coli
, allowing it to exploit nutrient patches in the marine
