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Organic chemist's contribution is essential to |
KEY TO UNLOCKING some of the mysteries of chemical signaling in aquatic species is the expertise and techniques of an organic chemist.
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In Georgia Tech's aquatic chemical signaling research initiative, chemist
Julia Kubanek, an assistant professor in the School of Biology and School of Chemistry and Biochemistry, provides that key. She employs chemical techniques in the laboratory to answer ecological questions and ultimately to address human health issues.
One of her primary studies – for which she recently received a National Science Foundation Career Award – centers on the chemically mediated interactions between aquatic microscopic plants and animals called phytoplankton and zooplankton.
Specifically, she is investigating why some phytoplankton get eaten and others – such as toxic algae – don't get consumed by zooplankton. Scientists believe certain chemical compounds defend some species of phytoplankton from predation. In laboratory experiments aimed at identifying these compounds, Kubanek incorporates various chemicals from phytoplankton into artificial food matrices that zooplankton either feed upon or ignore. To further understand these processes, Kubanek wants to determine the physiological effects of zooplankton's diets.
"Do they grow more slowly or lay fewer eggs because of the chemical compounds they consume or avoid?" Kubanek asks. "In turn, what effects does this selective eating have on the biology of phytoplankton? Similar questions have been asked and answered in terrestrial systems. For example, skunks are chemically protected from predators with the foul smell they can spray. But little work has been done in aquatic environments."
In other research, Kubanek is collaborating with School of Biology Professor Mark Hay on the chemical defenses of plants and animals that inhabit coral reefs. They want to know how those chemical defenses shape the ecological community.
"Are they a force for structuring the community and, in the long term, a force for the evolution of the community?" Kubanek asks. "We don't have a complete picture yet."
Kubanek and some colleagues at the Scripps Institution of Oceanography in San Diego, Calif., and the University of North Carolina at Wilmington have focused on marine sponge chemical defenses against coral reef fishes, against competing sponges, against settling larvae, and against biofilm-forming bacteria.
In laboratory experiments, researchers fed bits of sea sponge to fish and crabs, which spit it out. Then they extracted chemical compounds from the sponge, placed the extract on a piece of highly favored squid, and again the fish and crabs rejected the food, Kubanek explains. Next, they separated out thousands of chemical compounds from the sponge into water-soluble and non-water-soluble fractions. They combined the water-soluble fraction with a food pellet and fed it to fish and crabs, which again rejected the meal.
Kubanek is collaborating with School of Biology Professor Mark Hay on the chemical defenses of plants and animals that inhabit coral reefs. They want to know how those chemical defenses shape the ecological community. Here, Kubanek sorts specimens collected during a research cruise.
(300-dpi JPEG version - 59k)
Now, they are separating the water-soluble compounds into 10 fractions and testing each on a piece of squid provided to fish and crabs. The latter ignored only 10 percent of the treated squid, leaving researchers with several compounds to test further. They hope to soon discover the compound that fish and crabs find repulsive.
"It's probably a new compound," Kubanek says. "We have searched the literature for related species and haven't found any.... If we discover an exotic structure that affects predators, the commercial potential for this compound opens up."
Using this sort of ecologically driven assay is a new way for finding novel pharmaceuticals, Kubanek says. The rate of discovery of new drugs has slowed dramatically in recent years, but this method could improve that search.
As an example, Kubanek cites a study she started as a postdoctoral fellow at Scripps and has finished since she joined the Georgia Tech faculty. Kubanek and her colleagues investigated whether seaweeds in the ocean can avoid infection by fungi and bacteria by producing their own natural antibiotics. The seaweeds live in constant contact with potentially dangerous microbes, suggesting they are under pressure to evolve some kind of resistance, she explains.
Her colleagues at Scripps devised a bioassay to measure the antimicrobial potential of seaweeds. They combined biological extracts from seaweed with a fungus or bacterium and monitored the sample to see if the microbes grew. More than half of the 55 microbial species responded to some antibacterial property in the seaweed. This suggests that some natural compound in seaweeds is suppressing the growth of microbes, Kubanek explains.
It appears that the researchers have discovered a new antibiotic with a complex chemical structure that is somewhat similar to other antibiotics produced by terrestrial bacteria (thus researchers have not applied for a patent yet). The compound has a strong antifungal potency and potentially some cancer-fighting power, as well, Kubanek adds. The pharmaceutical company Bristol-Myers Squibb is a partner with Scripps and is collaborating on the ongoing research. Scientists still need to determine whether the seaweed is actually the original source of the antibiotic.
Meanwhile, Kubanek also collaborates with colleagues Jeannette Yen and Terry Snell (See Hot on the Trail and Avoiding Costly Mistakes.)
– Jane M. Sanders
courtesy of Julia Kubanek
For more information, contact Julia Kubanek, School of Biology, Georgia Tech, Atlanta, GA 30332-0230. (Telephone: 404-894-8424) (E-mail: julia.kubanek@biology.gatech.edu)
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Last updated: April 12, 2003