Metabolic flux analysis using stoichiometric models for Aspergillus niger: Comparison under glucoamylase-producing and non-producing conditions

Institute of Biochemical Engineering, Technische Universität Braunschweig, Gaussstr. 17, 38106 Braunschweig, Germany.
Journal of Biotechnology (Impact Factor: 2.87). 01/2008; 132(4):405-17. DOI: 10.1016/j.jbiotec.2007.08.034
Source: PubMed


Aspergillus niger AB1.13 cultures with glucoamylase production (with D-glucose as substrate) and without glucoamylase production (with D-xylose as substrate) were characterized by metabolic flux analysis. Two comprehensive metabolic models for d-glucose- as well as for D-xylose-consumption were used to quantify and compare the metabolic fluxes through the central pathways of carbon metabolism at different pH-values. The models consist of the most relevant metabolic pathways for A. niger including glycolysis, pentose-phosphate pathway, citrate cycle, energy metabolism and anaplerotic reactions comprising two intracellular compartments, the cytoplasm and mitochondrion. When D-xylose was used as the sole carbon source, the relative flux of the substrate through the oxidative pentose-phosphate pathway (PPP) via G6P-dehydrogenase was unaffected by the pH-value of the culture medium. About 30% of D-xylose consumed was routed through the oxidative PPP. In contrast, the flux of D-glucose (i.e., under glucoamylase-producing conditions) through the oxidative PPP was remarkably higher and, in addition was significantly affected by the pH-value of the culture medium (40% at pH 5.5, 56% at pH 3.7, respectively). Summarizing, the flux through the PPP under glucoamylase producing conditions was 30-90% higher than for non-producing conditions.

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Available from: Petra Dersch, Dec 08, 2014
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    • "In the following steps, the expression profile of the gene product needs to be analyzed and optimized, by means of adjusting the codon usage, overproduction of rate-limiting cofactors, metabolites or secretion components, and/or silencing of undesired byproducts. Rapidly increasing knowledge about fungal genomes and cellular functions by " Omic " technologies, flux analyses, and other global approaches (Andersen and Nielsen 2009; Breakspear and Momany 2007; Kim et al 2008; Wright et al 2009) will help to reconstruct the entire metabolic network with critical decision points, possible bottlenecks, and will allow a more precise modeling of protein production processes (Guebel and Torres-Daria 2001; David et al 2003; Melzer et al 2007). Ongoing development of high-throughput analysis of recombinant production strains and novel applications for genetic engineering will soon expand the possibility to optimize the fungal cell factory for industrial large-scale protein production processes and will further increase the value of Aspergilli as universal plodder for multi-step biotechnological fermentations. "
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    • "Similarly, the amplification of the protein assembly route itself, has been shown to result in enhancement of production in A. niger [48]. Beyond, these experimental studies on more obvious targets, flux balance analysis and also stoichiometric flux analysis indicate the importance of sufficient NADPH supply for protein production in A. niger [49,21] and A. oryzae [21,50] whereby the PPP plays an important role which was also found in the present study. "
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    • "When testing all combinations of two gene deletions, it was found that a fruitful strategy might be a deletion of ATP:citrate oxaloacetate-lyase and pyruvate decarboxylase giving a yield of at least 1.12 mol succinate per mol glucose. A smaller model of A. niger metabolism has been presented by Melzer et al. (2007) based on the model of David et al. (2003) and other information, and this model was used to predict metabolic fluxes through pathways of central metabolism in cultivations on two different media and at varying levels of ambient pH. A recently published comprehensive model of A. niger metabolism and the validation and analysis of it was presented by Andersen et al. (2008a). "
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