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Figure 14.4.
(Left) Topographic image of live
cell sitting on a Fe
2
O
3
substrate. (Right) Complementary afinity map, also known as a recognition force
microscopy image, collected with an anti-OmcA-functionalized tip.
51
Warm colours
(e.g., red) in the right image show the position of putative OmcA molecules produced
by the bacterium to form a bond with the mineral. The thin white oval outlines the
approximate location of the bacterium on the Fe(III) mineral.
S. oneidensis
Briely, this image was captured with so-called force-volume imaging
using an antibody-functionalized AFM tip (anti-OmcA). The tip was used to
collect a 32
32 grid of force curves across the cell and underlying mineral.
The energy (in attoJoules) of each individual force curve was determined by
integrating force with respect to distance. The energy of binding is shown
colours (e.g., blue indicates no bonds).
OmcA was not observed across the entire cell surface. Rather, it was
observed only at the cell's perimeter. Presumably, this cytochrome was also
located under the cell but hidden from the AFM tip as it scanned across the
top of the cell. Indeed, whole-cell spectra (see earlier) demonstrate that
OmcA can be located
s
the cell and mineral. This evidence strongly
suggests that OmcA is localized to the interface between
between
and the
Fe(III) mineral. It can therefore be inferred that OmcA (and MtrC) function in
the transfer of electrons from
S. oneidensis
S. oneidensis
to Fe(III) in the crystal structures
of minerals like FeOOH and Fe
2
O
3
.
14.5 SUMMARY
Most microorganisms on Earth live
solid surfaces such as pebbles in a
stream, quartz grains in a subsurface aquifer, clay aerosols loating in the
atmosphere or even apatite crystals in the human body. Intermolecular
and intramolecular forces play a central role in each instance regardless of
whether we, as humans, classify the interaction as environmental, geological
on
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