7 March 2020 | New Scientist | 15Microbiology Astronomy
Chris Baraniuk Leah Crane
SILVER seems to help prevent
harmful bacteria from spreading by
disrupting how they move around.
The precious metal has long
been used to stop the transmission
of bacteria – for example, in the
filters of some medical face masks
and in the antibacterial coatings
used on the International Space
Station. But until now, we didn’t
fully understand why it has
a sanitising effect.
To find out, researchers at the
University of Arkansas exposed
E. coli to small doses of positively
charged silver ions, which are
toxic to bacteria. They then used
a powerful microscope to watch
what happened to the bacteria’s
flagella – the whip-like motors
that bacteria use to move around.
Exposing the bacteria to silver
ions stalled their flagella, causing
the cells to “become much, much
slower”, says Yong Wang, one of
the researchers on the team. These
bacteria also changed direction
more, so they spent less time
moving in a line than non-exposed
bacteria (bioRxiv, doi.org/dnj6).
Silver has been used for decades
to stain flagella to make them easier
to see under the microscope, says
Jim Thomas at the University of
Sheffield in the UK. But this is
probably the first time its effect on
flagella has been studied, he says.
David Coil at the University of
California, Davis, says silver won’t
always have this effect because not
all bacteria have flagella. But silver
stops microbes in other ways too –
for instance, in higher doses, it
can damage cell walls and cause
bacteria to explode.
Stopping bacteria from moving
as easily makes it harder for them
to escape and therefore become
resistant to silver’s effects, says
Thomas. “Treatments that work
through multiple pathways or
targets are much more difficult
for bacteria,” he says. ❚
Secret of silver’s
antimicrobial
powers revealed
THE supermassive black hole
at the centre of the Milky Way
may have been crucial to the
evolution of life in our galaxy.
These days, the black hole,
known as Sagittarius A*, is
relatively calm. But there are
hints that it may have been
much more active millions
of years ago, swallowing
down matter and spewing out
high-energy radiation, including
large amounts of X-rays.
Xian Chen at Peking
University in Beijing, China,
and his colleagues simulated
how these X-rays would affect
the abundance of chemicals
crucial to the evolution of life:
water and organic molecules
such as methanol.
When high-energy photons,
like those of X-rays, hit
molecules, they can knock
off electrons. The resulting
molecules – and the free
electrons – tend to be more
likely to latch on to other
atoms or molecules, so thisinteraction can start a cascade
of chemical reactions.
The result can be ever
larger molecules, eventually
generating the complex
compounds required for life to
evolve. “Ultimately, maybe after
billions of years, this little energy
from a little photon created close
to a supermassive black hole
becomes part of a life,” says Chen.
The researchers found that
even as far away as 26,000 light
years from Sagittarius A*, which
is about the distance Earth sits
from it, many organic molecules
would be present at much
higher levels if the black hole
was once active than if it never
was. This effect could remain
for millions of years after the
activity ends, they calculated
(arxiv.org/abs/2002.03086).
“Right now, the black hole
is starved, but it’s possible
that a few million years ago
it was shining up to 100 million
times brighter,” says Avi Loeb
at Harvard University. “It
could have influenced the
material that made the sun,
the building blocks of life that
we find on Earth.”It is important to take this
sort of temporary event into
consideration when thinking
about the necessary conditions
for life to develop, says Loeb.
Because this kind of radiation
can also be extremely harmful
to planets too close to the black
hole, blowing away their
atmospheres and sterilising
their surfaces, there might bea fine line for planets to walk
in terms of where in the galaxy
they could host life.
Finding this line is still hard
because we don’t know exactly
what conditions are required for
life. “So far, we have established
the link between the activity
of the supermassive black hole
and the formation of some
basic building blocks of organic
and prebiotic molecules,”
says Chen. “But from building
blocks to a full-fledged life is
a long way, and there are still
many missing pieces.” ❚Galaxy’s black hole may
have helped life start
M.
KORN
MESS
ER
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AN
SOUTHE
RNOBSE
RV
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ORY/SCIENCE^ PHOTO
LIBRA
RYThe black hole at the
centre of the Milky Way
was once more active26,
Light years from the black hole
Sagittarius A* to Earth