Browsing by Author "Wang, Jasmin"

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  • Characterization and engineering of hexaric and hexuronic acid pathways in fungal microorganisms
    (2016-06-14) Wang, Jasmin
     Kemian tekniikan korkeakoulu | Master's thesis
    Citrus juice production and sugar beet processing produce pectin-rich residues which are mainly used as animal feed. Food industry also uses pectin produced from citrus peel as gelling agent. The main constituent of pectin is D-galacturonic acid. The filamentous fungus Aspergillus niger is naturally capable of hydrolyzing pectin and it can catabolize galacturonic acid through pyruvate and glycerol. Hence, pectin-rich residues could provide a cost effective alternative for producing value-added products, for example, galactaric acid which has many potential applications in polymer synthesis and as a platform chemical. Galactaric acid could be produced by engineered A. niger. However, the acid is catabolized by the mould resulting in the lowered yield. This catabolic pathway of galactaric acid is still not known. The objectives of the Master’s thesis were to unravel the pathway for galactaric acid catabolism, characterize the proteins and construct a galactaric acid producing A. niger strain. In this study, eight potential genes involved in the catabolic pathways were investigated. The genes were deleted from the wild-type strain ATCC 1015 utilizing CRISPR/Cas9 technology, and galactaric acid utilization of the resulting mutant strains was investigated. To the best of my knowledge, this is the first report of using in vitro gRNA successfully in A. niger for targeted gene deletion by the CRISPR/Cas9 genome editing tool. Three of the investigated genes, 39114, 1090836 and 1121140, were concluded to be involved in the pathway. Blocking galacturonic and galactaric acid pathways by deleting genes gaaA and 39114, respectively, and expressing a heterologous gene udh, A. niger ΔgaaA udh Δ39114 was able to produce 4.3 ± 0.2 g/l galactaric acid from galacturonic acid in submerged fermentation. In solid-state and submerged fermentation, the strain produced 15.4 ± 0.6 and 82.3 ± 3.9 mg galactaric acid/g citrus processing waste on dry mass basis, respectively.
  • Sellulaasientsyymien teollinen tuotanto
    (2013-04-25) Wang, Jasmin
     Kemiantekniikan korkeakoulu | Bachelor's thesis