title: Studies of the production of fungal polyketides in Aspergillus nidulans by using systems biology tools.
abstract: 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.
authors.affiliation: Center for Microbial Biotechnology, Department of Systems Biology, Building 223, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Gianni
authors.initials: G
authors.lastname: Panagiotou
authors.forename: Mikael R
authors.initials: MR
authors.lastname: Andersen
authors.forename: Thomas
authors.initials: T
authors.lastname: Grotkjaer
authors.forename: Torsten B
authors.initials: TB
authors.lastname: Regueira
authors.forename: Jens
authors.initials: J
authors.lastname: Nielsen
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Olsson
mesh_terms: D000217:Acyltransferases / Q000235:genetics; D000446:Aldehyde-Lyases / Q000235:genetics; D000818:Animals; D000924:Anticholesteremic Agents / Q000378:metabolism*; D001233:Aspergillus nidulans / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D019149:Bioreactors; D053898:Biosynthetic Pathways / Q000235:genetics*; D050260:Carbohydrate Metabolism; D005285:Fermentation; D020869:Gene Expression Profiling; D005800:Genes, Fungal; D005818:Genetic Engineering; D006801:Humans; D008025:Ligases / Q000235:genetics; D018942:Macrolides / Q000378:metabolism*; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics; D010407:Penicillium / Q000235:genetics; D011995:Recombination, Genetic; D049490:Systems Biology / Q000379:methods*; D014481:United States
chemical_list: D000924:Anticholesteremic Agents; D018942:Macrolides; D009097:Multienzyme Complexes; D010088:Oxidoreductases; D000217:Acyltransferases; D000446:Aldehyde-Lyases; C022367:phosphoketolase; C021587:6-methylsalicylic acid synthetase; D008025:Ligases