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UNNATURAL
3 involved an unusual rearrangement of
DNA that seems to have rewired the cell’s
What’s evolution ever done for us? Quite a lot
genetic circuitry in an unexpected way.
actually! From automobiles to antennas, scientists
The citrate eaters offer some clues to how
new species evolve. A new species needs a and engineers are exploiting evolutionary processes to
new ecological niche to occupy, so that it
won’t be outcompeted into extinction. In
improve existing technology and invent new ones
the case of E coli, the citrate in the broth
was a niche just waiting to be taken over. At
Nanotechnology
fi rst the bacteria did a poor job at feeding
As Darwin wrote in 1859, “multiply, vary, let the strongest live and the weakest die.” Popularly called ‘survival of the
on citrate, but they survived because they
fi ttest’, Darwin called this principle the one general law leading to the advancement of all organic beings. Now, 150
had no competition. Then, as they acquired years after On the Origin of Species was fi rst published, scientists are evolving organic beings to advance technology.
more mutations, they became better at their
At the Massachusetts Institute of Technology, Professor Angela Belcher is using viruses to grow new materials
new way of life.
for electronics, energy and medicine. Inspired by the way sea snails grow strong shells from calcium carbonate, she
wanted to see what nature could manufacture if it had the whole periodic table to play with.
Lenski and Blount predict that the
Belcher grows materials at the nanoscale by using M13 bacteriophage, a nanoscopic pencil-shaped virus that
mutations that make the bacteria better usually infects E coli. When outside of its bacterial host, the viral DNA is enclosed in a protective coat. Mutating one
at eating citrate would not be benefi cial
gene creates a billion different types of virus, varying only in the protein at the tip of their coats. Belcher then puts
to those that still feed on glucose. It’s a
them in a solution with a semiconductor. The mutation causes the virus tips to become attracted to the surface of the
semiconductor to differing degrees: the ‘strongest’ viruses are selected based on how good they are at clinging to
prediction they can actually test. Blount
the semiconductor, the weakest viruses are washed away. The survivors are allowed to multiply in bacteria and are
plans to insert the citrate-feeding mutations
then re-introduced to the semiconductor, this time under tougher conditions such as acidic solution. Repeating this
into the glucose-feeding bacteria to see selection process half a dozen times evolves viruses with a high affi nity for the semiconductor.
if they grow more slowly. If that proves
By mutating other genes that express proteins on the virus coat, Belcher can grow a shell of material around the
to be true, Lenski may be fi nally ready to
pencil-shaped virus, creating nano-wires. Combining two or more materials, such as gold and cobalt oxide,
produces nano-alloys. So far Belcher’s viruses have grown 40 different nano-materials for use in batteries, electrodes
treat the citrate eaters as a new species.
and solar cells.
He might call them Escherichia blountii,
or maybe Escherichia gouldii, after the late
palaeontologist Stephen Jay Gould.
Gould often wrote about how fl ukes
steered evolution in unexpected directions.
And certainly the citrate eaters in Lenski’s
lab support that. Blount tried to replicate
the evolution of citrate eaters, using their
own ancestors from different points in the
frozen fossil record, as well as other lines of
CHER E coli. He found that after about generation
20,000, some ancestors of the citrate-eaters
A BEL
could evolve to digest citrate. But none of
the other 11 lines could. In that one lineage,
, ANGEL
it seems some mysterious mutation opened
the door to the evolution of a new way of
life. Fortunately, Lenski and his colleagues
L UNIVERSITY
were there to see what came through.
Exactly what that mysterious mutation
did is yet another project for Lenski’s lab
COM, CORNEL
to study in years to come. The bacteria, it
Y
.
seems, are not done with him yet. “That’s
IBRAR the curse and beauty of science,” Lenski
T
OL
says with a rueful smile. �
A, PHO
AS
, N
Carl Zimmer is an award-winning
SS science writer. His latest book is
A nanobattery made with the
Microcosm: E coli and the
M13 bacteriophage virus
SPRE
New Science of Life
NEW
40 February 2009 www.bbcfocusmagazine.com
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