32 SCIENCE NEWS | April 23, 2022ALL: G.L. WEISSET AL/NATURE MICROBIOLOGY2022SCIENCE VISUALIZEDSome bacteria carry tiny syringes filled with chemicals that may
thin out competitors or incapacitate predators. Now, in two
types of bacteria, researchers have gotten up-close views of
these syringes — and found them in some unusual places.
Gregor Weiss, a cellular structural biologist at ETH Zurich,
and colleagues examined bacterial syringes using cryo-electron
microscopy, in which cells are flash frozen to capture cellular
structures as they look in nature (SN: 8/5/17, p. 12). Pre-
viously, researchers have found syringes anchored in
the outer membranes of bacteria. Some species shoot
their injectors’ payload into cells they bump into; others
squirt their contents into the environment.
But in a cyanobacteria called Anabaena, the syringes
are inside the cell, nestled in structures where the bac-
teria carry out photosynthesis, Weiss and colleagues
report in the March Nature Microbiology. One such
syringe can be seen in the image inset above (arrow);
the above illustration shows several syringes (tan)
piercing internal membranes (green). Buried inside the
cells, “it’s hard to imagine how [the syringes] could get
out and interact with the target organism,” Weiss says.
Each syringe consists of a molecular sheath
stretched over an inner tube filled with chemicals, the
team reports. Some signal, such as stress, causes a ring
at the syringe’s base (near the top of the visualization at
right, where colors denote different proteins) to open,Zooming in on bacteria weaponry
and the inner tube shoots out.
An Anabaena cell may use its syringes against itself to
trigger cell death when under stress, the team suggests. In
experiments, ultraviolet light or high salt levels triggered
some syringes to dump their payload. That led to the death of
some Anabaena cells in the long chains that the bacteria grow
in, forming hollow “ghost cells.” The ghost cells — which shed
their outer wall and membrane, exposing any remaining yet-
to-be-fired syringes to the outside world — may act like Trojan
horses, delivering their deadly payload to predators or
competitors, the team says.
In Algoriphagusmachipongonensis, a type of marine
bacteria, the syringes have a different architecture and
float unmoored, molecular biologist Charles Ericson,
also of ETH Zurich, and colleagues report in the same
issue of Nature Microbiology. The injectors were also
found in the liquid in which the bacteria were grown,
but how the syringes get out of the cell is a mystery.
Perhaps they are released when the bacteria die or, in
the wild, get eaten by a predator, Ericson says.
Comparing syringes from various species, the two
teams identified structures that are slightly different
from species to species. Learning how those modifi-
cations change the way the injectors work may help
scientists devise their own nanoinjectors that, for
example, direct antibiotics against troublesome bacte-
ria. “Now we have the general blueprint,” Ericson says.
“Can we re-engineer it?” — Tina Hesman Saey100 nmscivis.indd 32scivis.indd 32 4/6/22 9:44 AM4/6/22 9:44 AM