For Immediate Release
The finding helps explain why some seaweeds, sponges and corals appear
to avoid most infections by fungi and bacteria, according to a study published
May 19 in the Proceedings of the National
Academy of Sciences.
"Seaweeds live in constant contact with potentially dangerous microbes,
and they have apparently evolved a chemical defense to help resist disease,"
said lead author Julia
Kubanek, an assistant professor of biology and chemistry at the Georgia
Institute of Technology in Atlanta. "These plants have a really effective
way of defending themselves."
Few studies have addressed disease resistance in seaweeds, and seaweed diseases are little understood, except for species that are commercially important -- for example, the seaweed used for sushi. This study's report of isolating a potent antifungal compound contained in the common seaweed species Lobophora variegata reveals an unusual chemical structure not seen before in plants.
And the study lends insight into the ecological interactions between
this seaweed species and other marine organisms, Kubanek said. Also, it
presents the possibility of biomedical applications for the newly discovered
antifungal compound, she added.
The research -- funded in part by the National
Science Foundation -- was conducted in collaboration with colleagues
Jensen and William
Fenical at the Scripps Institution
of Oceanography in San Diego, Calif., Paul Keifer of Varian Inc. in
Palo Alto, Calif., and researchers M. Cameron Sullards and Dwight Collins
of Georgia Tech.
"Based on the antimicrobial activities we detected in a large survey
of many different algal species, it is possible that antimicrobial chemical
defenses are more common than previously believed and that L. variegata
may be one of many species that use natural antibiotics to defend against
infection," Jensen said.
Jensen devised a bioassay to measure the antimicrobial potential of the
common seaweed species, Lobophora variegata. He combined biological
extracts from seaweed harvested in the Bahamas with a fungus or bacterium
and monitored the sample to see if the microbes grew. Of the 51 samples
tested, 46 exhibited extraordinarily potent antifungal activity that could
be traced to exceedingly low concentrations of an antifungal compound
in the seaweed. Suppressed growth of microbes in the samples suggests
that a natural antimicrobial compound is at work, Kubanek explained.
"We have discovered a new antibiotic with a complex chemical structure
that structurally resembles two groups of macrolide antibiotics (i.e.,
those that kill fungi) -- one found in marine sponges and the other in
blue-green algae," Kubanek said. Because of the tiny available quantities
of this new compound, researchers have not applied for a patent yet.
The pharmaceutical company Bristol-Myers Squibb and a San Diego biotechnology
company, Nereus Pharmaceuticals Inc., are partners with Scripps and are
collaborating on related ongoing research. Scientists still need to determine
whether the seaweed is actually the original source of the antibiotic,
Kubanek added. The antimicrobial compound could be the byproduct of symbiosis
between the seaweed and an as-yet unidentified microbe. If this is the
case, it would be one of the rare examples of such a chemical defense
for plants and animals, researchers reported.
They believe that further investigations of chemically mediated interactions
between marine microbes and larger organisms are likely to reveal new
molecules and mechanisms that enable marine plants and animals to persist
despite intense microbial challenges, researchers wrote.
"Ecologically driven studies, such as this one, which used
marine fungi in operationally simple assays, may be a promising strategy
for uncovering novel natural products of commercial interest," the
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