Above, Salmonella typhirium. Scientists are utilizing the power of microbes (somewhat similar to these organisms shown here) in the hopes that it can deliver medication to patients at precise locations.
Hollywood has taught us that a journey inside the human body is a simple process requiring only a few key ingredients: adventurous participants, a vehicle to transport them, and a shrink ray. Cartoons like the Magic School Bus routinely show us what it’s like to cruise through swift-flowing blood streams to pulsating hearts and billowing lungs. In real life, scientists and doctors would love to travel deep inside their patients to help them when they’re sick. But shrink rays are hard to find on eBay, and even if we could shrink a 40 feet long school bus by a factor of 2 million to about 6 micrometers (the typical size of a red blood cell), unique forces that influence fluids at microscopic scales would make our school bus inoperable. Clearly, shrink rays won’t help us go deep inside the human body.
Did you know? Red blood cells are approximately 6-8 micrometers across. That’s 0.000006 meters, or roughly 1/14 the thickness of an average sheet of paper.
Unable to simply shrink down a traditional vehicle to a size small enough to fit inside the smallest human blood vessel, scientists have tried to design and build microscopic motors and propulsion devices, often only tens of atoms across. As you can imagine, manufacturing these systems is not easy, and scientists are still struggling to find a way to power these micro machines. Recently, Canadian scientists at L’École Polytechnique in Montreal led by Sylvain Martel have come up with a unique approach to this problem. Instead of reinventing the wheel, they plan to build on nature’s best miniature vehicle, the highly evolved and ever present bacterium.
Did you know? Scientists estimate that there are five nonillion (that’s 5 followed by 30 zeroes) bacteria on Earth. In the human body, there are approximately 10 times more bacteria cells than human cells!
Did you know? The bacteria strain that Martel’s group works is called MC-1, and it is one of the fastest around, able to travel up to 200 micrometers per second (ten times the speed of average bacteria) by spinning a tail-like device called a flagellum.
In addition to being the hot-rod of bacteria, MC-1 also has the unique property of having a string of magnetite crystals called magnetosomes. In nature, MC-1 and other types of magnetotactic bacteria use these crystals like a compass to follow the earth’s magnetic field to better environments. By manipulating the magnetic field surrounding the bacteria using large magnets like those found in MRI machines,scientists can trick MC-1 to go where they want them to.
Did you know? Bacterial flagella resemble hollow tubes made up of proteins. These tubes are attached to rotary proteins that use energy from a proton gradient to spin the flagella at a rate of up to 1000 rotations per minute to propel the bacteria.
Martel’s group hopes that eventually, they can use these MC-1 cells as vehicles to deliver drugs to the exact location where they are needed. They have injected 50 million MC-1 cells in rats and have shown that their presence do not harm their hosts and are completely destroyed by the rats immune system after 40 minutes.
Did you know? Earth’s magnetic field runs from north to south and many animals, including migratory birds use this magnetic field to navigate extremely long distances.
Did you know? The lab rat (Rattus norvegicus) has been a popular subject for experimental testing for over 200 years because it possesses many physiological similarities to humans. Recently, scientists have sequenced the rat genome, discovering that humans share approximately 1/4 th of our DNA sequences with both rats and mice.
This is a promising first step to accurate and precise drug deliver for humans. Who knows, one day we may inject ourselves with bacteria instead of killing them to help us feel better when we’re sick.
Article first published September 1, 2009
1) Bacteria take fantastic voyage through bloodstream (http://www.newscientist.com/article/dn17071-bacteria-take-fantastic-voyage-through-bloodstream.html)
2) Sylvain Martel, Mahmood Mohammadi, Ouajdi Felfoul, Zhao Lu and Pierre Pouponneau. (2008).
Flagellated Magnetotactic Bacteria as Controlled MRI-trackable Propulsion and Steering Systems for Medical Nanorobots Operating in the Human Microvasculature Through the Microscope.
The International Journal of Robotics Research. 28; 571
3) Blood Cells - Life's Blood; Wadsworth Center; New York State Department of Health (http://www.wadsworth.org/chemheme/heme/microscope/rbc.htm)
4) Whitman W, Coleman D, Wiebe W (1998). "Prokaryotes: the unseen majority". Proc Natl Acad Sci U S A 95 (12): 6578–83.
5) Laboratory Rat Gene Sequencing Completed; Humans Share One-fourth Of Genes With Rat, Mouse (http://www.sciencedaily.com/releases/2004/04/040401075930.htm)
David is a PhD candidate in the Department of Medical Genetics at the University of Toronto. He graduated from UBC with a Bachelor's in Biochemistry and Computer Science. During his spare time, David helps out with local science outreach programs like Let's Talk Science.