Ultra-fast communication allows aquatic cells to release toxins in unison, researchers say

Manu Prakash, an associate professor of bioengineering at Stanford University, was squatting in the mud of the Baylands Nature Reserve in Palo Alto. He scanned his Foldscope, an origami microscope of his own invention, scanning the inhabitants of the shallow waters of the marsh. With his eye drawn to a large single-celled organism called Spirostomum, he watched him do something that immediately made his next research topic.

"I still remember for the very first time this body swimming under the Foldscope," Prakash said. "It's a massive cell but it shrinks in less than a blink of an eye and accelerates faster than almost any other cell.When you do not expect it, it's like it's disappearing. to have been so excited that I had to bring the cells to the lab and take a close look. "

This observation, carried out with the aid of a simple tool located just five kilometers from the Prakash laboratory, led him and his colleagues to discover a new form of communication between cells, detailed in an article published on July 10 in Nature. Without touching or electrical or chemical signals, individual Spirostomums can coordinate their ultra-fast contractions so tightly that groups of them seem to contract simultaneously – a reaction to predators that synchronously releases paralytic toxins.

"There are many ways to communicate in biology, but it's really a new type of cell-to-cell signaling that we're trying to understand," said Arnold Mathijssen, a postdoctoral researcher at Prakash Lab and lead author of the paper. "It is possible that it is more universal than what we have described so far and that it allows many types of organisms to communicate."

Benches with black holes

The Prakash laboratory gathers wild samples of various microorganisms from an area called Peggy's Bench, named so with reference to a nearby memorial bench, and they've been coming here for years, often two or three times per week. A mixture of salt and fresh water, changing tides and migrations of birds make the marsh a hot spot of potential biodiversity. Although Prakash did not know anything about this during his first visit.

"Lake Lagunita was dry and I was looking for a new place to taste," recalls Prakash, referring to a small seasonal lake on the Stanford campus. "I looked at the GPS map on my phone and saw that blue dot, I did not know anything about it at first, but it was worth a try."

Back in the lab, the group studied wild specimens of Spirostomum while growing their own cultures of Spirostomum ambiguum and began to delve into the details of this ultra-fast contraction. Using high-speed imaging, they discovered that this occurred in 5 milliseconds (the human eye took from 100 to 400 milliseconds to flash) and that the cell withstood about 14 times the force of gravity of the process. In narrowing, pockets of toxin detach from the edges of the cell and release their contents into the surrounding liquid.

During a late night in the lab, the researchers also noticed that the cells all seemed to contract at the same time.

"We were wondering," How can cells close to a few centimeters synchronize to do something simultaneously? Said Bhamla, a former postdoctoral fellow at Prakash Lab, currently an assistant professor at Georgia Tech.

The researchers solved this mystery by applying the findings of various research conducted by Deepak Krishnamurthy, another graduate student at Prakash Lab, on how an individual cell can detect the movement of water around it. Once they observed the flow fields around Spirostomum, it appeared that they were communicating via hydrodynamic flows.

"The first cell contracts and generates a flow, which triggers the second and triggers the third, so you get that trigger wave that is spreading across the whole colony," Mathijssen explained. "These are large flows of long-range vortices and the communication speeds increase up to several meters per second, even though each cell is only 1 to 4 millimeters long."

Mathijssen understood what triggers the contraction of the first cell through an experiment that Prakash and Krishnamurthy had already built for Krishnamurthy's research. By carefully aspirating the liquid from a small hole in a pair of slides containing S. ambiguum, Mathijssen imitated the dietary action of his predators. The closer the cell was to the hole, the more one end of its body was stretched in relation to the other, as happens when an object approaches a black hole. With this simple and relatively large experiment, the researchers determined that a specific amount of body tension was likely to cause the opening or closing of voltage-dependent ion channels within S. ambiguum, which she contracted it.

Where the wild things are

Prakash and Bhamla laboratories are continuing their work on S. ambiguum to learn more about how, when and why these cells contract. They also want to know if the hydrodynamic communication they have discovered is being used by other organisms because in nature, creating and detecting flow is essential for survival. As part of this research and other work, Prakash Lab regularly returns to Peggy's Bench.

"Although this place was an accidental discovery for me, we are working on several projects in the lab that have been inspired by what we have collected here," said Prakash, while standing on the edge of the swamp. "This work is only one example of the many hidden gems we can find when we leave the lab – and whoever has simple tools, like Foldscope, can discover and begin to explore."

In the near future, Prakash plans to conduct an extensive biodiversity survey in the Swamp where they will collect Spirostomum, which would include creating a live video on the aquatic world's microscope of their subjects and inviting undergraduates to explore this swampy area.