7 September 2019 | New Scientist | 17AstrophysicsA JUMBO virus has evolved a
CRISPR-like immune system to
defend against smaller viruses
that attack it. A team in France
has confirmed how it works by
transferring the entire system to
a bacterium and tweaking it to
destroy a different target.
While CRISPR has become
famous as a tool geneticists canuse for editing genomes, it evolved
in bacteria as a way of defending
against viruses. The bacteria
“cannibalise” bits of DNA from the
viruses that attack them and add
this to their own genomes. This
allows them to recognise and
destroy any matching viral DNA
the next time they get attacked.
In 2016, Didier Raoult at
Aix-Marseille University in France
claimed that a giant virus called
mimivirus had independently
evolved a CRISPR-like system,
dubbed MIMIVIRE, that helped itrecognise and destroy a virus called
zamilon, but critics questioned this.
So Raoult and his colleagues have
now transferred the MIMIVIRE
system to an E. coli bacterium.
Crucially, they swapped zamilon
DNA for bits of a gene within the
E. coli genome. When they activated
MIMIVIRE in the E. coli, it destroyed
that gene (bioRxiv, doi.org/c9z2).This shows that the system
isn’t specific to zamilon, and that
a mimivirus could almost instantly
acquire resistance to a different
invading virus by cannibalising its
DNA, says Raoult. His team is now
searching for strains of mimivirus
that have done this.
It might be possible to adapt
MIMIVIRE for gene editing, as has
been done with CRISPR variants
from bacteria and another branch of
single-celled life known as archaea.
But Raoult has no plans to try this. ❚EARLY on 28 August, gravitational
wave detectors felt two ripples in
space-time wash over them. But
due to a strange effect of general
relativity, both may actually be
from the same event.
Gravitational waves, which
stretch and compress space-time,
emanate from massive objects
smashing together. The Laser
Interferometer Gravitational-
Wave Observatory (LIGO) has
seen the waves from more than
30 such events since 2015. Another
detector, Virgo in Italy, has also
come online. Multiple detectors
make it possible to find more
signals and figure out where they
came from more precisely.
The two signals that came in
last week are unusual in ways
that have led some astronomers
to say they might be from a single
source. For one thing, they hit the
detectors just 21 minutes apart,
making this only the second time
two gravitational waves have been
spotted in one day. The black holes
that merged to make the signals
are also in roughly in the same
place in the sky. And they are at
similar distances from us, between
5 and 6 billion light years away.
Two waves could result from asingle collision because of an
effect known as gravitational
lensing. This normally refers to
how the gravity of a massive object
warps the path of light. In this case
the idea is that it might have bent
the path of the gravitational wave.
“It would look like two separate
events, but it’s really one event
that’s being split into two by a
large object in the way,” says
Asantha Cooray at the University
of California, Irvine.
This could account for the time
delay between the two signals: if
the gravitational waves were splitand bent, the later signal might
come from waves that had to
travel further along a curved path
to get to our detectors. Such a
short delay means that the lensing
object would have to be something
relatively small and compact, like a
black hole, Cooray says. “If a whole
galaxy was lensing this, the time
delay would be much larger.”
Some members of the LIGO
collaboration say this is probablynot the case. “It is much more
likely that the localisation and
distance of the candidates
coincide by chance than that
the source aligned with a lensing
object in its way,” says LIGO team
member Gabriela González at
Louisiana State University.
Also, while the areas the signals
seem to have come from are close,
they don’t align precisely. If they
come from a single event, they
must be in exactly the same spot.
This doesn’t completely rule
out a gravitationally lensed wave.
“The preliminary localisations are
regularly seen to shift upon final
analysis,” says LIGO team member
Derek Fox at Pennsylvania State
University. So although they don’t
appear to line up exactly at the
moment, that could change.
We will find out for sure
whether the waves are from
two events or one when LIGO
and Virgo analyse the signals
further over the coming months.
If a single merger of black holes is
responsible, it could teach us more
about not only binary black holes
but also the sort of objects that can
act as a lens and bend the waves
from them. “If they are lensed
it’s a pretty big deal,” says Fox. ❚Microbiology
Colliding black holes
create detectable
ripples in space-timeLeah CraneTHE SIMULATING EXTREME SPACETIMES (SXS) PROJECTDouble cosmic signal is a puzzle
Two gravitational waves picked up in quick succession could have the same source
Giant virus has its
own kind of CRISPR
to destroy invadersMichael Le Page400
The length, in nanometres, of mimivirus,
one of the largest known viruses