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Fig. 1.6
Genome-enabled techniques contribute to the development of models of how microorganisms function in
contaminated environments. (Source: Derek R. Lovley
2003
Nature Reviews)
that
Geobacter metallireducens
specifically pro-
duces flagella only when the organism is grow-
ing on insoluble Fe(III) or Mn(IV) oxides. Genes
for chemotaxis were also evident in the
Geo-
bacter
genomes, and experimental investiga-
tions have revealed that
G. metallireducens
has
a novel chemotaxis to Fe(II),which could help
guide it to Fe(III) oxides under anaerobic con-
ditions (Nevin and Lovley
2002
). Pili genes are
present and are also specifically expressed dur-
ing growth on insoluble oxides. Genetic studies
have indicated that the role of the pili is to aid in
attachment to Fe(III) oxides, as well as facilitat-
ing movement along sediment particles in search
of Fe(III) (Fig.
1.7
).
This energy-efficient mechanism for locat-
ing and reducing Fe(III) oxides in
Geobacter
species contrasts with the strategies for Fe(III)
reduction in other well-studied organisms,
such as
Shewanella
and
Geothrix
species.
These other organisms release Fe(III) chela-
tors, which solubilize Fe(III) from Fe(III) ox-
ides, and electron shuttling compounds, which
accept electrons from the cell surface and then
reduce Fe(III) oxides. These strategies make it
possible for
Shewanella
and
Geothrix
species
to reduce Fe(III) without directly contacting the
Fe(III) oxide.
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