Frontiers in Squid Reproduction: Prospecting for New Antibiotics

May 1, 2002

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

Female squid cut open to show internal anatomy. (left)

Ten years ago, Professor David Epel at Hopkins Marine Station of Stanford University, challenged his students to explain a curiosity of squid reproduction. Female squid lay their eggs on the bare seafloor, without burying, or in any way protecting, their offspring. They congregate, drop their eggs and jet off into the wild blue yonder. Still, somehow, the 1-millimeter-wide eggs survive for the 30 days it takes the eggs to develop and hatch. They don't rot. They don't get fungal infections and many avoid predation.

"How do these eggs manage to survive disease?" Epel asked. "Why don't they rot?" The answer, it turns out, could lead to new medicines.

At the time, Epel suggested that squid eggs must contain natural antibiotics that prevent bacterial and

Female laying eggs on ocean bottom [from a video frame from Sea Studios (below)]

fungal infections. The eggs, he reasoned, must be nearly sterile.

To his surprise, his own experiments proved him incorrect and directed his research along an intriguing new path.

Instead of being bacteria free, he found that squid eggs teem with bacteria and are absolutely covered in them. Yet the eggs stay healthy. In subsequent work, he showed that female squid possess a gland that secretes bacteria onto their eggs, as they are released from their body. He compared the gland to a tube of toothpaste that squeezes out "bacteria paste." The paste inoculates the eggs.

"We are not sure what the bacteria are doing," he said. Almost certainly they are producing antibacterial or antifungal compounds. He and colleagues have discovered that not just California squid but squid around the world secrete protective coatings on their eggs.

(left) Cross section of accessory nidamental gland with DNA stain. Cell nuclei on the sides of pockets and bacteria in the pockets are visible. (right) Baby Squid Hatchling

California Sea Grant is currently funding Epel to identify the bacteria on eggs of California market squid --- one of the state's most commercially valuable fisheries --- and to characterize the antibacterial and antifungal properties associated with these bacteria.

So far, Epel and his colleagues have identified more than six different species of bacteria on egg cases of the market squid, Loligo opalescens. He believes that this suite of bacteria may interact, through chemical signals, to produce antimicrobial compounds.

His work has many commercial applications. Fish farmers are always looking for new medicines to fight diseases. The compounds could also lead to drug discovery for people.

Current antibiotics kill bacteria by inhibiting cell wall or protein synthesis. Epel said, "The holy grail would be to discover an antibiotic that works through a new mechanism. Bacteria would not be resistant to such a medicine."