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Appl Environ Microbiol, April 1998, p. 1490-1496, Vol. 64, No. 4
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Evidence that a New Antibiotic Flavone Glycoside Chemically Defends the Sea Grass Thalassia testudinum against Zoosporic Fungi

P. R. Jensen,^1,* K. M. Jenkins,¹ D. Porter,² and W. Fenical¹

Scripps Institution of Oceanography, Center for Marine Biotechnology and Biomedicine, University of California- San Diego, La Jolla, California 92093,¹ and Department of Botany, University of Georgia, Athens, Georgia 30602²

Received 19 September 1997/Accepted 23 January 1998

Significantly fewer thraustochytrid protists (zoosporic fungi) were observed in association with healthy leaf tissue of the marine angiosperm Thalassia testudinum than in association with sterilized samples that were returned to the collection site for 48 h. In support of the hypothesis that sea grass secondary metabolites were responsible for these differences, extracts of healthy T. testudinum leaf tissues inhibited the growth of the co-occurring thraustochytrid Schizochytrium aggregatum and deterred the attachment of S. aggregatum motile zoospores to an extract-impregnated substrate. By using S. aggregatum for bioassay-guided chemical fractionation, a new flavone glycoside was isolated and structurally characterized as luteolin 7-O--D-glucopyranosyl-2"-sulfate. Whole-leaf tissue concentrations of this metabolite (4 mg/ml of wet leaf tissue) inhibited S. aggregatum attachment, and a significantly lower concentration (270 µg/ml) reduced thraustochytrid growth by 50%, suggesting that natural concentrations are at least 15 times greater than that needed for significant microbiological effects. These results offer the first complete chemical characterization of a sea grass sulfated flavone glycoside and provide evidence that a secondary metabolite chemically defends T. testudinum against fouling microorganisms.

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^* Corresponding author. Mailing address: Scripps Institution of Oceanography, Center for Marine Biotechnology and Biomedicine, University of California-San Diego, La Jolla, CA 92093-0236. Phone: (619) 534-7322. Fax: (619) 558-3702. E-mail: pjensen{at}ucsd.edu.

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