Abstract
Aspergillus carbonarius has potential as a cell factory for the production of different organic acids. At pH 5.5, A.carbonarius accumulates high amounts of gluconic acid when it grows on glucose based medium whereas at low pH, it produces citric acid. The conversion of glucose to gluconic acid is carried out by secretion of the enzyme, glucose oxidase. In this work, the gene encoding glucose oxidase was identified and deleted from A. carbonarius with the aim of changing the carbon flux towards other organic acids. The effect of genetic engineering was examined by testing glucose oxidase deficient (Δgox) mutants for the production of different organic acids in a defined production medium. The results obtained showed that the gluconic acid accumulation was completely inhibited and increased amounts of citric acid, oxalic acid and malic acid were observed in the Δgox mutants.
Highlights
With depletion of crude oil and increased environmental concern, biologically based processes for producing organic acids that can be used as building blocks in the chemical industries have begun to raise attention in recent years (Holladay et al 2007)
In this study we investigated the effect of deleting the glucose oxidase in Aspergillus carbonarius for the purpose of organic acid production at pH 5–6
In the present work, a glucose oxidase gene in A. carbonarius involved in gluconic acid production was identified and deleted
Summary
With depletion of crude oil and increased environmental concern, biologically based processes for producing organic acids that can be used as building blocks in the chemical industries have begun to raise attention in recent years (Holladay et al 2007). In A. niger, production of citric acid was dramatically suppressed at near neutral pH as gluconic acid started accumulating in high amount (Bercovitz et al 1990; Goldberg et al 2006). In this study we investigated the effect of deleting the glucose oxidase in Aspergillus carbonarius for the purpose of organic acid production at pH 5–6. At this pH range, the fungus accumulates high amounts of gluconic acid, presumably due to secretion of glucose oxidase, whereby the fungus quickly converts glucose into gluconic acid outside the cell preventing further metabolism of glucose (Mischak et al 1985). A Ku complex deficient strain of A. carbonarius (Gallo et al 2012), which is supposed to dramatically increase the homologous recombination frequency due to the inactivation of Ku complex, was selected for this work
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