Biology Reference
In-Depth Information
In contrast, the Arctic bacterium
C. psychrerythraea
has developed an
enhanced antioxidant capacity owing to the presence of three copies of cat-
alase genes as well as two superoxide-dismutase genes, one of which codes
for a nickel-containing superoxide-dismutase, never reported before in
proteobacteria (
Meth´ et al., 2005
).
Ph
TAC125 copes with increased O
2
solubility by deleting entire meta-
bolic pathways that generate ROS as side products. It is worth noting
that, despite the availability of molybdate in sea water (
Hille, 2002
),
Ph
TAC125 not only lacks the molybdate biosynthetic and transport genes
but also genes encoding enzymes using molybdate as cofactor, for example,
trimethylamine N-oxide reductase, xanthine oxidase, biotin sulphoxide
reductase and oxido-reductase YedY (
Loschi et al., 2004
).
The
Ph
TAC125 genome also contains all genes required for the pentose
phosphate pathway (
M´digue et al., 2005
); moreover, glucose-6-phosphate
dehydrogenase (Zwf;
PSHAa1140
), transketolase (TktA;
PSHAa0671
) and
transaldolase (TalB;
PSHAa2559
) have been found in the cytoplasmic
proteome (
Wilmes et al., 2011
). This feature increases the concentration
of NADPH, which in turn provides high levels of reduced thioredoxin that
can help to protect against the toxic effects of O
2
. Therefore, to develop
better oxidative stress adaptation in the cold,
Ph
TAC125 can use the pentose
phosphate pathway for carbohydrate inter-conversion.
In order to cope with the improved stability of ROS at low tempera-
tures, iron-related proteins are down-regulated at 4
C(
Piette et al.,
2011
), presumably to avoid oxidative cell damage induced by the deleterious
Fenton reaction (
Valko, Morris, & Cronin, 2005
). Cell protection may be
achieved by dioxygenases that are coded in large number in both chromo-
somes (
M´digue et al., 2005
). Moreover, O
2
-consuming lipid desaturases
protect against toxic O
2
by increasing the membrane fluidity at low temper-
ature (
M´digue et al., 2005
).
A further tool, possibly related to the peculiar features of the Antarctic
habitat, may be the synthesis of globins facilitating several biological
functions, including protection from nitrosative and oxidative stress (see
Section 6.2.4
).
5.4. Biotechnological applications
Microorganisms are an interesting source of cold-active enzymes endowed
with biotechnological potential. Enzymes from psychrophiles have recently
received increasing attention, because they offer novel opportunities in
