19 October 2019 | New Scientist | 15SOMETHING strange is going on
in the deep sea. Luminous bacteria
have teamed up with predatory
anglerfish, which seem to use the
glowing microbes to help catch
prey. The bacteria have evolved
to depend on the anglerfish, yet
they may spend much of their
time floating freely in the water.
Anglerfish have large teeth,
and protruding from the heads
of females is a long, thin growth
called an esca, which resembles
a fishing line. Its tip is often
luminous, and might help some
anglerfish living in the pitch-black
deep sea to lure in prey.
But we don’t know for sure, says
Tory Hendry at Cornell University
in New York. Anglerfish biology
is so mysterious that the only
evidence we have that the esca
is a lure is that it looks like it
should be one, she says.
Hendry and her team are now
beginning to throw some light
on anglerfish ecology, with a
particular focus on the luminous
bacteria living in their escas.
They previously found that these
bacteria have lost about 50 per
cent of their DNA, and with it
many abilities. “They rely onAnglerfish may collect
their glowing bacteria
OceansMichael MarshallDOUG PERRINE/GETTY IMAGESglucose from the host,” she says.
This discovery implied that the
bacteria spend all their lives inside
anglerfish, but Hendry and her
colleagues have now overturned
this. They sequenced the DNA
of the bacteria found in the
escas of seven anglerfish species.
One species of anglerfish had its
own unique bacteria, but all the
others shared the same species
of symbiotic bacteria.
The only explanation is that
the bacteria live in the water and
the anglerfish collect them, says
Hendry. This implies the bacteria
are widespread, because anglerfish
from both the North Atlantic and
Gulf of Mexico had the same
species (eLife, doi.org/dchh).
“There has to be an
environmental pool that all
these fish are getting their
symbionts from,” says Hendry.
The team found that the
bacteria have lost many genes,
making it harder for them to
survive alone. Why might this be?
It may not be an adaptation,
says Hendry. The team also found
signs of rogue pieces of DNA
called transposable elements,
which can disrupt genes and
may have triggered the losses.
The secret to the bacteria’s
survival could lie in a chemical
called polyhydroxybutyrate (PHB).
Many bacteria use it to store
carbon for lean periods. Hendry
says the bacteria may accumulate
glucose from anglerfish, then
store it as PHB and live off that
when they return to the water.
She speculates that some
anglerfish may even seed the
water with bacteria. They have
mysterious knobs on their back
that also hold bacteria, but which
are opaque so they can’t glow.
“We know they have a pore on
them, so presumably the bacteria
can leave the host and go out into
the environment,” says Hendry. ❚ALL space rockets operate on
the principle of action-reaction:
by blasting material one way,
they travel in the opposite one.
But one NASA engineer believes
he could take us to the stars
without any propellant at all.
The “helical engine” designed
by David Burns at NASA’s
Marshall Space Flight Center in
Alabama exploits mass-altering
effects that occur at close to
light speed. Burns has posted a
paper describing the concept on
NASA’s technical reports server.
It has been met with
scepticism, but Burns believes
his concept is worth pursuing.
“If someone says it doesn’t
work, I’ll be the first to say ‘it
was worth a shot’,” he says.
To get a sense of Burns’s
engine, picture a box on a
frictionless surface. Inside is a
rod, along which a ring can slide.
If a spring inside the box gives
the ring a push, the ring will slide
along the rod one way while the
box recoils in the other direction.
When the ring reaches the end
of the box, it will bounce back,
and the box’s recoil direction
will switch too. This is action-
reaction, or Isaac Newton’s
third law of motion. In normal
circumstances, it restricts the
box to wiggling on the spot.
But, Burns asks, what if the
ring’s mass is much greater
when it slides in one direction
than the other? Then it would
give the box a greater kick at
one end than the other and the
box would accelerate forwards.
Einstein’s theory of special
relativity says objects gain
mass as they are driven towards
the speed of light. In fact, a
simplistic implementation of
Burns’s concept would be to
replace the ring with a circular
particle accelerator, in which
ions are swiftly accelerated
to relativistic speeds during
one stroke and decelerated
during the other.
Burns thinks it would
make sense for the engine to
essentially be a helical particle
accelerator. It would need to
be big: 200 metres long and
12 metres in diameter. It would
also require 165 megawatts of
power to generate just 1 newton
of thrust, about the same force
you use to type on a keyboard.For that reason, the engine
would reach meaningful
speeds only in the frictionless
environment of space. “The
engine itself would be able
to get to 99 per cent the speed
of light if you had enough
time and power,” says Burns.
Propellant-less proposals
aren’t new. For example, in the
early 2000s, British inventor
Roger Shawyer proposed the
EM drive, which he claimed
could convert microwaves
into thrust. The concept hasn’t
been demonstrated and is
widely assumed to violate
the laws of physics.
“All inertial propulsion
systems, to my knowledge,
never worked in a friction-free
environment,” says Martin
Tajmar at the Dresden University
of Technology in Germany.
Burns’s machine makes use
of special relativity, unlike the
EM drive, which complicates
the picture, says Tajmar.
Burns, who worked on
his design without NASA
sponsorship, admits his concept
is inefficient, but says it might
be improved by harvesting
wasted heat energy. ❚Physics
Jon Cartwright
Anglerfish employ
glowing bacteria in
their “fishing rods”Helical engine
could break the
laws of nature
200m
Length of particle accelerator
needed in a helical engine