Page 127 - 79_04

Beatriz
Baselga-­-Cervera&
col.

isotopes
in
ecosystems
is
well
known
that
biological
enzymes
sometimes
produce

isotopic
fractionation
(34).

As
is
well
known,
uranium
found
in
nature
consists
largely
of
two
isotopes,

238U
and
the
less
abundant
235U,
which
constitutes
only
approximately
0.7%
of

naturally
occurring
uranium.
Most
of
the
commercial
nuclear
power
reactors

require
uranium
enriched
in
the
235U
(35).

Biological
fractionation
of
U
has
been
recently
tried
by
an
indirect

procedure
linking
bacterial
uranium
reduction
to
the
isotopic
partitioning
(36).

However,
one
step
uranium
enrichment
by
preferential
uptake
of
an
isotope

directly
using
a
microorganism
not
been
implemented
yet.
Chlamydomonas

isolated
from
the
uranium
polluted
site
of
Saelices,
was
tested
for
U
fractionation.

For
this,
the
uranium
isotopic
composition
in
water
of
Saelices
evaporation
pond

was
compared
with
the
isotopic
ratio
of
U
bio-­-accumulated
by
Chlamydomonas

(previously
the
cells
were
treated
with
EDTA
to
eliminate
metals
on
the
cell
wall).

The
analysis
through
a
High
Resolution
Inductively
Coupled
Plasma
Mass

Spectrometry
(HR-­-ICPMS)
let
to
obtain
the
isotopic
distribution
of
uranium.

The
results
obtained
reveal
that
Clamydomonas
is
able
to
U
fractionation

(d235U
inside
the
cells
with
respect
to
235U
in
Saelices
evaporation
pond
was
-­-3.5

%).
This
spectacular
result
indicates
that
microalgae
are
capable
of
producing

uranium
fractionation
effectively.
A
microalgae
plant
for
uranium
enrichment

could
be
a
real
possibility.

6.
CONCLUSIONS

Once
more
nature
has
won
the
race
to
the
human
technology:

Microorganisms
were
able
to
adapt
to
extreme
U
contamination
as
well
as

accumulate
and
perform
isotopic
fractionation
of
uranium
to
become
the
most

feasible
creators
of
the
first
nuclear
reactor
in
Oklo
1.7
billion
years
ago.
The

extreme
environment
of
the
evaporation
pond
in
Saelices
uranium
mine
provides

some
ideas
of
how
microorganisms
can
build
a
nuclear
reactor.
Microalgae
seem

good
candidates
for
nuclear
engineers:

First
of
all
they
were
able
to
adapt
to
the
extreme
U-­-contaminated

environment
of
Saelices
mining
area
in
less
than
40
years.
These
algae
had
suffered

a
pressure
of
selection
in
which
pre-­-adaptive
mutations
that
confer
resistance

against
the
toxic
effect
of
uranium
can
survive.

Second
efficient
biological
accumulation
of
uranium
(115
mg
U/g
dry
mass)

was
demonstrated.

Finally,
microalgae
are
able
to
successfully
carry
out
an
isotopic
fractioning

of
uranium.

642