Some bacteria carry tiny syringes filled with chemicals that could cripple competitors or incapacitate predators. Now, researchers have taken a close look at these syringes, technically known as constriction injection systems, from a cyanobacteria and a marine bacterium.
Figuring out how key parts of molecular injectors work could help scientists design their own nanomachines. Manual injection machines can guide antibiotics against troublesome bacteria without affecting friendly microbes.
Genes encoding injection machinery components are found in many bacterial species. But, “just by looking at the genes, it’s hard to predict how these constriction-injection systems work,” says Gregor Weiss, a structural cell biologist at ETH Zurich.
So Weiss and colleagues used cryo-electron microscopy to examine bacterial syringes, in which cells are snap-frozen to capture cellular structures as they usually look in nature (SN: June 22, 2017).
Previously, researchers discovered syringes that were anchored to the outer membranes of certain bacteria, allowing the bacteria to shoot their payloads into the cells they bumped into. Syringes of other species eject their contents into the environment.
But in a species called cyanobacteria Anabaenathe syringe is in an unusual place, Nestled in the membranes of the internal structures of bacteria that carry out photosynthesisWeiss and colleagues report in March nature microbiology. Buried in a cell, “It’s hard to imagine how [the syringes] can go out and interact with target organisms,” Weiss said.
Anabaena When cyanobacteria are stressed, they may use their syringes to trigger programmed cell death on themselves. In the team’s experiments, UV light or high salt levels in the water triggered some syringes to dump their payloads.This has led to some deaths Anabaena Cyanobacteria grow in long chains of cells that form hollow “ghost cells.”
Ghost cells shed their outer walls and membranes, exposing unlit syringes in the inner membrane. The team speculates that these ghosts may act like Trojan horses, delivering lethal payloads to predators or competitors.Researchers have yet to discover which organisms are possible targets Anabaenas syringe.
Inside a species called marine bacteria Anteater, the story is a little different.Here, the syringe Has a different structure and floats inside bacterial cellsCharles Ericson of ETH Zurich and colleagues report in March Nature Microbiology. Syringes have also been found in liquids in which bacteria are grown in the lab, but how they got out of the cells has been a mystery. Perhaps the bacteria are released when they die or are eaten by predators, Erickson said.
The team also found that two proteins loaded in Anteater syringes, but the role of these proteins is unclear.Researchers try genetic engineering Escherichia coli One of the proteins is produced, but it kills the bacteria, said study co-author Jingwei Xu of ETH Zurich.
The researchers compared the structures of syringes from different species and found that some structures inside the machines were similar but varied by species. Understanding how these modifications change the way the syringes work may allow researchers to load different cargoes into the tubes or target the syringes to specific bacteria or other organisms. “Now that we have the overall blueprint,” Erickson said, “can we redesign it?”