By Wallace Marshall
Co-director, MBL Physiology Course
Last month, I had a problem. I was teaching in the MBL Physiology course, using the giant, single-celled organism Stentor as a model system for students to learn quantitative approaches in cell biology. Stentor, which live in ponds, eat by creating a vortex of water that drags food into the cell’s mouth. The flow is created by thousands of cilia—tiny, hair-like cell parts that swing back and forth pushing fluid around. (Cilia are also critical for making the mucus in your airway flow away from your lungs, and patients with defects in these cilia can be really sick. So the question of how cilia make fluid flow is very important from a medical perspective. )
Stentor is a genus of large, trumpet-shaped ciliates, commonly found in freshwater ponds. Credit: EOL / micro*scope
One of the students in our class, Shashank Shekhar from the CNRS Institute, France, had become interested in how the cell generates this pattern of fluid flow. Shashank started tracking the flow by putting small plastic beads into the water around the Stentor and then taking video images of the beads moving. This is a pretty standard approach in fluid dynamics called particle image velocimetry (PIV). But it’s not that commonly used in biology, and we didn’t entirely know what we were doing. The software we had been trying to use to track these particles didn’t give really nice flow lines. So this was the problem: How to use the flow of these tiny beads to figure out the pattern of flow around the cell as it feeds.
Frustrated by this problem, I decided to go get some coffee from Woods Hole Market. On the way back, I ran into my colleague Magdalena Bezanilla, an MBL Whitman Investigator from University of Massachusetts, Amherst, who works on cell biology. She thinks a lot about things moving inside cells so I figured I could get her input into our PIV challenge.
We ended up chatting about the problem in the MBL’s Waterfront Park, and while we were talking, a couple of guys emerged from the harbor in full scuba gear, carrying a huge metal bracket upon which was mounted a video camera and a laser. (This would be quite weird back home but it’s business as usual in Woods Hole.) I asked the guys what they were up to and they said they were using PIV to study the flow of fluid around ctenophores! Ctenophores or comb jellies are jellyfish-like animals that swim using cilia. So at the exact moment that we were pondering how to use PIV to track cilia-generated fluid flow in our single-celled organisms in the Physiology course, a guy walks out of the water and announces that he is doing the exact same thing, for comb jellies! (Those people who say that Woods Hole is a magical place are telling the truth.)
The guys with the scuba gear and lasers were Jack Costello of Providence College and Sean Colin of Roger Williams University, Whitman Investigators working for the summer at the MBL. Jack offered to give us advice about how to analyze our data, so I sent Shashank over to Jack’s lab in the Rowe building. With Jack’s help and expertise, Shashank was able to get beautiful flow lines from his data (see photo), which clearly reveal the pattern of cilia-generated flow around the Stentor cell while it feeds. Our big problem was solved in a single day due to a fortuitous combination of people, courses, coffee breaks, cells, beaches, marine organisms, and advanced technology. And that’s what summer at the MBL is all about.
Fluid flow around Stentor as it feeds, visualized by particle image velocimetry. Courtesy of Wallace Marshall.
Thank you to Wallace Marshall of the University of California, San Francisco, for contributing this post. All MBL scientists, students, community members, and visitors are invited to submit items for the MBL’s blog. Please contact Diana Kenney: firstname.lastname@example.org.