Engineering Aspergillus niger for galactaric acid production: elimination of galactaric acid catabolism by using RNA sequencing and CRISPR/Cas9

Joosu Kuivanen (Corresponding Author), Jasmin Wang, Peter Richard

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Abstract

Background: meso-Galactaric acid is a dicarboxylic acid that can be produced by the oxidation of d-galacturonic acid, the main constituent of pectin. Mould strains can be engineered to perform this oxidation by expressing the bacterial enzyme uronate dehydrogenase. In addition, the endogenous pathway for d-galacturonic acid catabolism has to be inactivated. The filamentous fungus Aspergillus niger would be a suitable strain for galactaric acid production since it is efficient in pectin hydrolysis, however, it is catabolizing the resulting galactaric acid via an unknown catabolic pathway. Results : In this study, a transcriptomics approach was used to identify genes involved in galactaric acid catabolism. Several genes were deleted using CRISPR/Cas9 together with in vitro synthesized sgRNA. As a result, galactaric acid catabolism was disrupted. An engineered A. niger strain combining the disrupted galactaric and d-galacturonic acid catabolism with an expression of a heterologous uronate dehydrogenase produced galactaric acid from d-galacturonic acid. The resulting strain was also converting pectin-rich biomass to galactaric acid in a consolidated bioprocess. Conclusions: In the present study, we demonstrated the use of CRISPR/Cas9 mediated gene deletion technology in A. niger in an metabolic engineering application. As a result, a strain for the efficient production of galactaric acid from d-galacturonic acid was generated. The present study highlights the usefulness of CRISPR/Cas9 technology in the metabolic engineering of filamentous fungi.
Original languageEnglish
Article number210
JournalMicrobial Cell Factories
Volume15
DOIs
Publication statusPublished - 2016
MoE publication typeA1 Journal article-refereed

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Keywords

  • aspergillus niger
  • metabolic engineering
  • CRISPR
  • pectin
  • d-galacturonic acid
  • galactaric acid
  • mucic acid
  • uronate dehydrogenase

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