A team of researchers including UMCES-IMET scientist Dr. Allen Place has discovered that a microbe commonly found in the Chesapeake Bay emits a poison not just to protect itself but to stun and immobilize the prey it plans to eat.
The researchers studied the behavior of the algal cell Karlodinium veneficum, known as a dinoflagellate and found in estuaries worldwide.
This particular species is known to release a substance called karlotoxin, which is extremely damaging to the gills of fish. K. veneficum has been known to form large algal blooms in the Chesapeake and elsewhere, triggering an immediate harmful impact on aquatic life, including fish kills.
“This new research opens the door to reducing bloom frequency and intensity by reducing the availability of its prey,” says Dr. Place, in whose laboratory karlotoxin was discovered and characterized. “As we reduce the nutrient load feeding Karlodinium’s prey and bring back the bay's most prolific filter feeder, the Eastern oyster, we could essentially limit Karlodinium’s ability to bloom.”
“This is a major environmental problem, but we didn’t know why these microbes were producing the toxins in the first place,” adds research collaborator Dr. Joseph Katz of Johns Hopkins. “Some people thought they were just using the toxins to scare away other predators and protect themselves. But with this new research, we’ve provided clear evidence that this species of K. veneficum is using the toxin to stun and capture its prey.”
Historically, scientists have found it difficult to study the behavior of these tiny animals because the single-cell creatures can quickly swim out of a microscope’s shallow field of focus. But in recent years this problem has been solved through the use of digital holographic microscopy, which can capture three-dimensional images of the troublesome microbes.
In a study published in 2007, Katz, Place and Jian Sheng were part of a team that reported the use of digital holographic microscopy to view the swimming behavior of K. veneficum and Pfiesteria piscicida. At the time, it appeared that K. veneficum slowed down into a “stealth mode” in order to ambush its prey while P. piscicida sped up to capture prey.
In a more recent paper published in the Proceedings of the National Academy of Sciences, the researchers used the same technique to more closely study the relationship between K. veneficum and its prey, a common, single-celled algal cell called a cryptophyte. They found that K. veneficum microbes release toxins to stun and immobilize their prey prior to ingestion, probably to increase the success rate of their hunt and to promote their growth.
This significantly shifts the understanding about what permits harmful algal blooms to form and grow, the researchers said. Instead of being a self-defense mechanism, the microbes’ production of poison appears to be more closely related to growth through the ingestion of a “pre-packaged” food source, the cryptophyte cell, they concluded.
Funding for the research was provided by the National Science Foundation and the National Oceanic and Atmospheric Administration’s Coastal Oceans Program.
