The Johns Hopkins Gazette: January 12, 1998

Jan. 12, 1998
VOL. 27, NO. 17


Scientist Is Always Chasing Fireflies

Spotlight: Bioluminescence expertise brings Howard Seliger recognition for his lifetime work

Emil Venere
News and Information

Johns Hopkins Gazette Online Edition

As a boy growing up in a poor family on the Lower East Side of Manhattan during the 1930s, Howard Seliger looked forward to summer camp in rural New Jersey.

The free camp, operated by a private settlement house, offered city kids their first exposure to nature.

"I saw fireflies and I was fascinated by them," recalls Seliger, a professor in the Department of Biology.

Howard Seliger, a biochemist, was recently named a fellow of the American Association for the Advancement of Science.

Many years later, he would revisit his boyhood fancy for fireflies. After establishing himself as a nuclear physicist, Seliger took his career in an entirely new direction; he came to Johns Hopkins in 1958 for a one-year Guggenheim Fellowship to study bioluminescence, a living organism's ability to make light through biological processes.

Seliger never left.

He forged a new career in biochemistry, and his work in bioluminescence has led to advances in everything from ecology to cancer research.

"What he's accomplished is amazing," says William Biggley, who became Seliger's research assistant in 1962. "All I can say is, you want to come to work every day when you work with Howard Seliger."

Before coming to Johns Hopkins, Seliger plied his trade for 10 years as a physicist at what was then the National Bureau of Standards, in Washington, D.C.

"He had written a lot of papers that are still relevant today," Biggley said. "You see them quoted all the time. Just recently an instrument he designed in the 1950s was on the cover of the Health Physics Society journal. It blew me away when I saw it."

Biggley says he marveled at how Seliger has routinely shifted from one specialty to another throughout his career.

"You could be working in one field on something that was reasonably important, and then he would just change hats and go over to something that was entirely different," he says. "And if you were part of that project, you got to be somewhat involved in it, and it was pretty heady stuff."

Biggley isn't the only person who thinks highly of his colleague. Seliger recently earned a rare honor: He was named a fellow of the American Association for the Advancement of Science.

The fellowship recognizes him for a lifetime of research.

"And if that doesn't make you feel old, nothing will," says Seliger, who will formally accept the award on Feb. 14, during an annual meeting of the AAAS in Philadelphia.

However, Seliger says, his work is far from finished.

He currently is trying to develop a system for testing human memory by seeing how precisely people remember colors. Because wavelengths of light can be measured very accurately, such a method might enable doctors to better assess how a patient's memory changes over time, possibly as a result of stroke, coronary bypass surgery or Alzheimer's disease.

"I am using the measurement of wavelength as a means of determining the precision of memory, rather than asking somebody to repeat a bunch of words they've heard," Seliger says.

Chalk it up as another bold idea.

"He tends to shake the field up when he does this," Biggley says. "He sort of has radical ideas, and the established experts wonder, who is this guy? It's interesting to watch it happen, but he's done that all his life."

In addition to his ongoing research, Seliger teaches a freshman seminar called Light and Life; he presents a series of lectures about bioluminescence in an advanced biochemistry course; and he offers a course in radiobiology, the study of how radiation affects living organisms.

"I would say the fascination of his whole life has been light," says a longtime colleague, biology professor Ludwig Brand.

Seliger has exploited that fascination to probe scientific mysteries in various fields, daring to cross boundaries other researchers might consider foreign turf.

"He's just one of these scientists who has had a very broad career," Brand says. "And I think he's been outstanding at training students."

But his Johns Hopkins career began as a temporary experiment. As a Guggenheim fellow, Seliger joined a group of scientists headed by William McElroy, a biochemist who was an expert on bioluminescence and chairman of the Biology Department from 1956 to 1969.

"I said, 'Well, I don't know any biochemistry, but I do know physics,' " Seliger says.

Over the years, he essentially became a biologist, sitting in on lectures, studying and working in the field.

"If you've ever dealt with physicists before, you know that, because they have the mathematical background, they feel everything else is easy," Seliger says. "It is and it isn't. You still need to do a lot of work."

Since those early days at Hopkins, his research interests have extended from physics to oceanography, ecology to the origins of the first forms of life.

"It's been interesting, 35 years of working with him," Biggley says. "You never knew where he was going next. You'd say, 'Wait a minute; this is not going to result in anything.' And the next thing you knew, we were off."

Seliger's training as a physicist enabled him to analyze the fundamental workings of bioluminescence. Using spectroscopy--the separation of radiation into its component wavelengths or colors- -he probed the living light shows displayed by various species of fireflies and microscopic aquatic algae called phytoplankton.

The team of Hopkins scientists studied many of the roughly 200 species of fireflies in Jamaica and Maryland. Scientists had known that fireflies recognize members of their own species by the pattern in which they flash light. What appears to the human eye as one long flash is actually a series of very rapid signals emitted in a specific pattern characteristic of only one species.

Amid the seemingly random flashing of numerous fireflies on a summer evening, individual males and females of the same species are actually using a sort of Morse code to signal each other.

So Seliger built an instrument he called a "firefly gun," which measured the firefly flash patterns as they occur in nature.

"The reason to develop this firefly gun was that if you capture a firefly and put it in a bottle, it will be nervous and it won't emit its natural flash patterns," he says.

The scientists used the gun in the field to identify the flash patterns of certain species. Then they captured the insects, identified them and brought them back to the laboratory, where they could conduct detailed experiments on their bioluminescence.

Their spectral analyses led to the surprising revelation that different species of fireflies emit their own specific colors. But that finding puzzled scientists; if certain insect species only recognize each other by their respective flash patterns, why should it matter what color light they emit?

Seliger's research revealed the answer. Depending on the environment and time of day in which a firefly comes out, certain colors will be easier to see. Over millions of years of evolution, the insects developed their own hues of bioluminescence, optimizing their sensitivity to detect one another's flashes.

"We could actually look at a firefly's bioluminescence and tell you what time of day it became active," he says.

James Lloyd, a behavioral entomologist at the University of Florida who specializes in fireflies, fondly remembers his work with Seliger. From the 1960s through the 1980s, Lloyd would send the hundreds of live fireflies he had captured to Seliger's lab, where the insects' bioluminescence was analyzed.

"I'm still kind of a solitary field person," Lloyd says, "but that was a very long and a very rewarding interaction."

During the 1970s and 1980s, Seliger traveled to Jamaica and Puerto Rico to study "bioluminescent bays" full of light-producing phytoplankton, organisms that make oxygen and are vital to the food chain. The research uncovered important findings about the plankton ecology at a time when habitats were increasingly threatened by environmental ills.

Working in Jamaica, however, carried its own special risks.

There was the time that Seliger and Biggley, working in an instrument-laden boat in the middle of a Jamaican bay, were mistaken for drug runners and hauled off to jail.

An airplane had crashed nearby, and police were in hot pursuit of apparent smugglers.

"They had a police boat out in the water, as well as guys all over the shore, looking for these desperados," Biggley says. "Here we were in the water making measurements with all this equipment. It looked very technical. We had a communications type thing, and the police were certain that they had the right people. Absolutely certain.

"They put us in a car and took us to the local jail, which really must have been a holdover from the colonial days because it was pretty grim."

The Hopkins researchers spent most of the afternoon behind bars before they were cleared.

"We laugh now, but we were not amused at the time," Biggley says.

But the risks were well worth the scientific benefits. Seliger was able to use what he learned in the bioluminescent bays of Jamaica and Puerto Rico to solve a biological whodunit, of sorts, in the Chesapeake Bay.

In the 1960s, officials were hard-pressed to figure out what was killing fish in large numbers. It was possible that blooms of a species called Prorocentrum maria lebouriae, which appear suddenly each summer in the northern Chesapeake Bay at the Bay Bridge, were responsible for the extensive fish kills.

Seliger and his group were the first to trace the seasonal movement of those particular phytoplankton and to demonstrate how they travel under water, providing a model for the transport of such organisms in coastal waters and estuaries throughout the world. The model has been shown predict the extent and timing of blooms of toxic phytoplankton in coastal regions as far removed as Spain, southern California, western Florida, Borneo and New Guinea.

"We were able to show that Prorocentrum began in the rivers at the Virginia mouth of the bay and were transported all the way into the northern bay, where they were upwelled at the Bay Bridge," Seliger says. "When they were upwelled, they formed the surface blooms.

Meanwhile, the findings absolved the Prorocentrum; they were not responsible for the fish kills. Instead, the culprit was runoff from agriculture, soil erosion, city storm drains and sewage-treatment plants. Organic nutrients in the runoff fed thriving populations of bacteria, which consumed oxygen during the night, making the dark waters anoxic. The fish died from lack of oxygen. However, in the light of day the water seemed perfectly normal because the phytoplankton carried out photosynthesis after sunrise, replenishing the oxygen supply.

In the work for which he is perhaps best known, Seliger's firefly research helped other scientists harness bioluminescent molecules to identify key sections of DNA for genetic studies. And he used such fluorescent molecules to probe carcinogenic compounds in cigarette smoke. He also was able to see which potentially carcinogenic compounds became most dangerous by measuring the low-intensity light produced as the compounds react with enzymes inside cells.

The whirlwind of research in Seliger's lab seemed to generate a gravity all its own, Biggley said.

"We were very busy, but it was very interesting," he says. "I think that was the whole thing. You thought that you were participating in something that was really worthwhile."