Enhancing isoprimeverose-producing enzyme in genetically engineered Aspergillus oryzae through impeller shape and pH...

Aspergillus oryzae is a filamentous fungus that serves as a source of polysaccharide-degrading enzymes. We constructed two self-cloning forms of A. oryzae that specifically express isoprimeverose oligoxyloglucanase (IpeA) and endoglucanase. These enzymes are essential for the enzymatic release of the rare sugar isoprimeverose (α-D-xylopyranosyl-(1→6)-D-glucopyranose) from tamarind xyloglucan. Of the two, IpeA is a key enzyme that is currently unavailable commercially. The primary objective of this study was to enhance IpeA production through fermentation engineering. Various fermentation parameters were optimized. These include a source of carbon from either glucose or maltose, pH control, and impeller shapes using either Disk Turbine (DT) or MAXBLEND® (MB) impellers that were tested using a 5-L stirred-tank bioreactor. Cultivation in maltose-supplemented medium resulted in a reduction in carbon catabolite repression compared with that of glucose. Batch fermentation at acidic pH (4.5) using the MB impeller yielded a significantly higher level of biomass and enzyme production with a dry mycelial weight (DMW) yield of ∼19 g/L and IpeA activity of ∼68 U/mL, which compares favorably with ∼14 g/L of DMW and 43 U/mL of IpeA activity under identical pH conditions when using a DT impeller. The findings of this study offer valuable insight for both large-scale and biological production of A. oryzae.