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Applied and Environmental Microbiology, April 2009, p. 2212-2220, Vol. 75, No. 7
0099-2240/09/$08.00+0 doi:10.1128/AEM.01461-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Studies of the Production of Fungal Polyketides in Aspergillus nidulans by Using Systems Biology Tools
,
Gianni Panagiotou,1,
Mikael R. Andersen,1,
Thomas Grotkjaer,2
Torsten B. Regueira,1
Jens Nielsen,1,
and
Lisbeth Olsson1*
Center for Microbial Biotechnology, Department of Systems Biology, Building 223, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark,1 Fluxome Sciences A/S, Diplomvej 378, DK-2800 Kongens Lyngby, Denmark2
Received 30 June 2008/ Accepted 8 January 2009
Many filamentous fungi produce polyketide molecules with great significance as human pharmaceuticals; these molecules include the cholesterol-lowering compound lovastatin, which was originally isolated from Aspergillus terreus. The chemical diversity and potential uses of these compounds are virtually unlimited, and it is thus of great interest to develop a well-described microbial production platform for polyketides. Using genetic engineering tools available for the model organism Aspergillus nidulans, we constructed two recombinant strains, one expressing the Penicillium griseofulvum 6-methylsalicylic acid (6-MSA) synthase gene and one expressing the 6-MSA synthase gene and overexpressing the native xylulose-5-phosphate phosphoketolase gene (xpkA) for increasing the pool of polyketide precursor levels. The physiology of the recombinant strains and that of a reference wild-type strain were characterized on glucose, xylose, glycerol, and ethanol media in controlled bioreactors. Glucose was found to be the preferred carbon source for 6-MSA production, and 6-MSA concentrations up to 455 mg/liter were obtained for the recombinant strain harboring the 6-MSA gene. Our findings indicate that overexpression of xpkA does not directly improve 6-MSA production on glucose, but it is possible, if the metabolic flux through the lower part of glycolysis is reduced, to obtain quite high yields for conversion of sugar to 6-MSA. Systems biology tools were employed for in-depth analysis of the metabolic processes. Transcriptome analysis of 6-MSA-producing strains grown on glucose and xylose in the presence and absence of xpkA overexpression, combined with flux and physiology data, enabled us to propose an xpkA-msaS interaction model describing the competition between biomass formation and 6-MSA production for the available acetyl coenzyme A.
* Corresponding author. Present address: Department of Chemical and Biological Engineering, Industrial Biotechnology, Chalmers University of Technology, Kemivägen 10, SE-412 96 Gothenburg, Sweden. Phone: 46 31 772 3805. Fax: 46 31 772 3801. E-mail: lisbeth.olsson{at}chalmers.se
Published ahead of print on 23 January 2009.
Supplemental material for this article may be found at http://aem.asm.org/.
G.P. and M.R.A. contributed equally to this study.
Present address: Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
Applied and Environmental Microbiology, April 2009, p. 2212-2220, Vol. 75, No. 7
0099-2240/09/$08.00+0 doi:10.1128/AEM.01461-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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