2000). Furthermore, low Taxol concentrations, comparable to the levels we detected in endophyte extracts, did not affect the physiological properties of the membrane (Balasubramanian and Straubinger 1994; Sharma and Straubinger 1994; Bernsdorf et al. 1999; Crosasso et al. 2000; Zhao and Feng 2004). Although these experiments involved artificial membranes, there is also evidence

that fungi can take up non-polar compounds by passive transport and store them in vesicles. For example, Fusarium solani can absorb polyaromatic compounds from the cell culture medium and store them within intracellular compartments with no impact on growth (Verdin et al. 2005). In the endophytes we studied, the accumulation of non-polar taxoid molecules in lipophilic cell structures combined with the high sensitivity of our analytical methods, immunological detection and LC/MS/MS-based multi-reaction monitoring (MRM) ensured that these PI3K Inhibitor Library carry-overs could be detected. After the first and second passages of the fungal cultures, no taxanes could be detected by LC/MS/MS. The fungi were no longer associated with the Taxol source and 4EGI-1 in vitro hence the trace amounts of taxanes detected initially were diluted below the detection limit. Our

results and conclusions therefore offer a satisfactory explanation for the contradictory results in earlier publications, some providing evidence for independent taxane biosynthesis in different endophytic fungi and others lacking this evidence. Acknowledgments U.H. was supported by a pre-doctoral fellowship from the Volkswagen Foundation, Hannover, Germany (AZ.: I/82 754). Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source

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