Biology Reference
In-Depth Information
Fe
2
O
3
Fe
Fe
Fe
Fe(III) '
OM
Fe
2
O
3
Fe
e
-
Reduction
TonB
transport system(s)
Fe(II)
Oxidation
FutA2
Fe(III)
Fe
Fe
Fe(III) '
PM
FutB
FeoB
FutC
Figure 3.7
Uptake pathway model for Synechocystis PCC 6803. See the colour plate.
uptake (Rose et al., 2005;
Shaked, Kustka, Morel, & Erel, 2004
). Therefore,
it is possible that in
Synechocystis
PCC 6803, reduction occurs in the peri-
plasmic space before transport through the plasma membrane (
Fig. 3.7
).
In other cyanobacterial species, some work has been done to demonstrate
the bioavailability of Fe′. In the siderophore-producing cyanobacterium
Anabaena flos-aquae
, siderophore-independant uptake of inorganic iron was
shown under Fe limitation (
Wirtz, Treble, & Weger, 2010
). The relations
between siderophore and non-siderophore uptake pathways in cyanobacte-
ria warrant further investigation.
2.6.3. Reductive siderophore uptake
Ferrisiderophore reduction outside the plasma membrane has been studied
in the nonphotosynthetic bacterium
P. aeruginosa
. In this organism, sidero-
phores are secreted by the cell, ferrisiderophores are actively transported
through the outer membrane and then the complex is reduced in the peri-
plasm before transport across the plasma membrane. The siderophores are
recycled from the periplasm back into the environment (
Greenwald et al.,
2007
). In
Synechocystis
PCC 6803, short-term iron uptake of Fe′ was com-
pared with that of FeDFB. DFB binds Fe so strongly (Martell and Smith,
1975) that with the excess chelator used, no Fe′ was present in the medium
(
Kranzler et al., 2011
). Experiments were done using medium containing
either 0.12 nM Fe′ or 100 nM FeDFB. Despite the large difference in the
pool of bioavailable iron, Fe′ was transported with remarkable efficiency
