artificial bacterial flagella
Posted on by Dr. Francis Collins
Nanoparticles hold great promise for delivering next-generation therapeutics, including those based on CRISPR gene editing tools. The challenge is how to guide these tiny particles through the bloodstream and into the right target tissues. Now, scientists are enlisting some surprising partners in this quest: magnetic bacteria!
First a bit of background. Discovered in the 1960s during studies of bog sediments, “magnetotactic” bacteria contain magnetic, iron-rich particles that enable them to orient themselves to the Earth’s magnetic fields. To explore the potential of these microbes for targeted delivery of nanoparticles, the NIH-funded researchers devised the ingenious system you see in this fluorescence microscopy video. This system features a model blood vessel filled with a liquid that contains both fluorescently-tagged nanoparticles (red) and large swarms of a type of magnetic bacteria called Magnetospirillum magneticum (not visible).
At the touch of a button that rotates external magnetic fields, researchers can wirelessly control the direction in which the bacteria move through the liquid—up, down, left, right, and even “freestyle.” And—get this—the flow created by the synchronized swimming of all these bacteria pushes along any nearby nanoparticles in the same direction, even without any physical contact between the two. In fact, the researchers have found that this bacteria-guided system delivers nanoparticles into target model tissues three times faster than a similar system lacking such bacteria.
How did anyone ever dream this up? Most previous attempts to get nanoparticle-based therapies into diseased tissues have relied on simple diffusion or molecular targeting methods. Because those approaches are not always ideal, NIH-funded researchers Sangeeta Bhatia, Massachusetts Institute of Technology, Cambridge, MA, and Simone Schürle, formerly of MIT and now ETH Zurich, asked themselves: Could magnetic forces be used to propel nanoparticles through the bloodstream?
As a graduate student at ETH Zurich, Schürle had worked to develop and study tiny magnetic robots, each about the size of a cell. Those microbots, called artificial bacterial flagella (ABF), were designed to replicate the movements of bacteria, relying on miniature flagellum-like propellers to move them along in corkscrew-like fashion.
In a study published recently in Science Advances, the researchers found that the miniature robots worked as hoped in tests within a model blood vessel . Using magnets to propel a single microbot, the researchers found that 200-nanometer-sized polystyrene balls penetrated twice as far into a model tissue as they did without the aid of the magnet-driven forces.
At the same time, others in the Bhatia lab were developing bacteria that could be used to deliver cancer-fighting drugs. Schürle and Bhatia wished they could direct those microbial swarms using magnets as they could with the microbots. That’s when they learned about the potential of M. magneticum and developed the experimental system demonstrated in the video above.
The researchers’ next step will be to test their magnetic approach to drug delivery in a mouse model. Ultimately, they think their innovative strategy holds promise for delivering nanoparticles carrying a wide range of therapeutic payloads right to a tumor, infection, or other diseased tissue. It’s yet another example of how basic research combined with outside-the-box thinking can lead to surprisingly creative solutions with real potential to improve human health.
 Synthetic and living micropropellers for convection-enhanced nanoparticle transport. Schürle S, Soleimany AP, Yeh T, Anand GM, Häberli M, Fleming HE, Mirkhani N, Qiu F, Hauert S, Wang X, Nelson BJ, Bhatia SN. Sci Adv. 2019 Apr 26;5(4):eaav4803.
What are genome editing and CRISPR-Cas9? (National Library of Medicine/NIH)
Sangeeta Bhatia (Massachusetts Institute of Technology, Cambridge, MA)
Simone Schürle-Finke (ETH Zurich, Switzerland)
NIH Support: National Cancer Institute; National Institute of General Medical Sciences