Cellular localisation of secondary metabolites isolated from the Caribbean sponge Plakortis simplex
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The Caribbean sponge, Plakortis simplex, is known to contain a large array of secondary metabolites, including the antimalarial polyketide plakortin, several unusual glycolipids, and some hopanoids, which closely resemble typical bacterial metabolites. The hypothesis that they could be products of bacterial metabolism was tested by localizing specific metabolites in cells using physical separation of sponge cells, bacterial symbionts and supernatant by differential centrifugation. The obtained fractions were analysed separately for the typical P. simplex metabolites by NMR and mass spectrometry, and most of them were shown to be present in the bacterial cells but not in the sponge cells. In addition, PCR screening showed that the biosynthetic pathway for glycosphingolipids was present in the bacterial cells. Isolation of a Sphingomonas strain PS193 from P. simplex and subsequent glycosphingolipid analysis resulted in the detection of a known glycosphingolipid, GSL-1, that did, however, not match the glycosphingolipid profile of P. simplex. Therefore, it is unlikely that Sphingomonas strain PS193 is an abundant member of the microbial community associated with P. simplex. Other glycosphingolipid producing bacteria in P. simplex remain to be identified. In conclusion, this study provides experimental evidence that the glycolipids and hopanoids and possibly also the polyketide plakortin are produced by microbial symbionts rather than the sponge from which the metabolites were originally isolated.
KeywordsSponge Polyketide Cell Separation Sphingomonas Marine Sponge
The authors are very grateful to Prof. J. R. Pawlik, UNCW for inviting them to participate to the third Pawlik expedition during which the material was collected, and to Prof. M. Pansini, University of Genova for the sponge taxonomy determination. Mass and NMR spectra were recorded at the “Centro di Servizi Interdipartimentale di Analisi Strumentale”, Università di Napoli “Federico II”. The assistance of the staff is gratefully acknowledged. This research project is funded by the Italian Government, MIUR PRIN (Italy) and by the CEE “Marie Curie Host Fellowship Contract no. HPMD-CT-2001-101. This study was also supported by grants of the DFG (SFB630 TP A5) and the bmb+f (BiotecMarin: 03F0414E) to U. Hentschel.
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