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By Rachel Ehrenberg
new experiments failed to confirm that
a microbe called GFAJ- 1 (shown) incor-
porates arsenic into its DnA.
to what Wolfe-Simon and colleagues
thought might have been in their culture anyway.
GFAJ- 1 then grew much better. In
fact, it grew in densities similar to those
Wolfe-Simon and her colleagues had
reported for GFAJ- 1 when arsenic was
added. And adding or removing arsenic
from the cultures made no difference in
growth, Redfield and her team report.
“At this point the discussion is essentially over,” says Benner, who was not
involved with the work.
Nonetheless, Redfield then extracted
and purified GFAJ- 1’s DNA. The samples
did contain trace amounts of arsenate,
but not in the ratios one would expect
if the microbe had incorporated arsenate into its cellular machinery. It’s
more likely, says Redfield, that GFAJ- 1
can tolerate a bit of arsenic here or there
without any serious effects.
“You can grow a bug in arsenic-rich
media and you will see some arsenate,”
says geobiologist Tanja Bosak of MIT.
But that does not mean the arsenate is
in the DNA, she says.
Wolfe-Simon, who says she can’t comment in detail until Redfield’s results
appear in a peer-revie wed journal, wrote
in an e-mail that her original paper never
actually claimed that arsenate was being
incorporated in GFAJ- 1’s DNA, but that
others had jumped to that conclusion.
“As far as we know, all the data in our
paper still stand,” she wrote. “Yet, it may
take some time to accurately establish
where the [arsenic] ends up.” s
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