Sea Slug Mixes Chemical Defense Before Firing At Predators

When threatened by predators, sea slugs defend themselves by ejecting a potent inky secretion into the water consisting of hydrogen peroxide, ammonia and several types of acids. A team of researchers with the Atlanta-based Center for Behavioral Neuroscience (CBN) has found that this secretion is produced from normally inert chemicals stored separately in two glands. The discovery, published in the Dec. 16 on-line edition of the Journal of Experimental Biology, provides insight into a natural chemical process with potential industrial applications.

>In the study, a research team led by Georgia State University biologist Charles Derby, PhD, examined the ink and opaline glands of Aplysia sea slugs for the chemicals L-lysine, L-arginine and an enzyme protein called escapin. In previous research, Derby's team determined that escapin mediates the chemical reaction with L-lysine and L-arginine that results in the defensive secretion. Using a variety of chemical and molecular techniques, the scientists identified L-lysine and L-arginine in the opaline gland, which produces the sticky white component of the secretion, and escapin in the ink gland, which produces the purple dye in the secretion.

"Aplysia packages these innocuous precursors separately and then releases them simultaneously into its mantle cavity at the precise time when they are needed," explained Derby. "This mechanism insures the secretion's potency against attacking predators to enable sea slugs to escape."

Aplysia employs a variety of mechanisms to defend against predators. Its secretion stimulates feeding behaviors in spiny lobsters, but deters these behaviors in other animals. In previous studies, Derby and his team also identified an antimicrobial property in the secretion resulting from the chemical reaction between escapin and L-lysine. The scientists are currently examining the chemical process that results in the antimicrobial component and also are attempting to identify Aplysia predators which are affected by this property of the secretion.

"The antimicrobial property probably evolved to work against predators," said Derby. "But it might also function as an antimicrobial salve for Aplysia's own wounds."

Derby's team, who discovered escapin and holds a provisional patent for its genetic sequence, has been studying the protein for its potential applications as an antimicrobial compound for the healthcare and marine industries. The team has determined that escapin prevents the growth of all major forms of bacteria as well as other microbes.

"As we learn more about how escapin works in Aplysia, we will hopefully be able to reproduce its chemical properties in the laboratory," said Derby.

In addition to Derby, co-authors of the Journal of Experimental Biology study are Paul Johnson, PhD, Cynthia Kicklighter, PhD, Manfred Schmidt, PhD, Michiya Kamio, PhD, Hsiuchin Yang, PhD, and Phang Tai, PhD, of the Georgia State biology department. Other co-authors include physiologists Dimitry Elkin and William Michel, PhD, of the University of Utah School of Medicine.

Derby's research is supported by grants from the National Science Foundation, National Institutes of Health and the Georgia Research Alliance.

CBN, a National Science Foundation Science and Technology Center, is a research and education consortium of eight metro Atlanta colleges and universities. More than 90 neuroscientists lead the interdisciplinary research program to understand the neurobiology of complex social behaviors. CBN studies have led to a breakthrough treatment for anxiety-related disorders and new understanding of the neurochemicals vasopressin and oxytocin in social behavior. In addition to research, CBN has a comprehensive education program designed to improve science literacy and attract more women and underrepresented minorities to neuroscience programs. The center is supported by more than $53 million in grants from NSF and the Georgia Research Alliance.