GpdA-promoter-controlled production of glucose oxidase by recombinant Aspergillus niger using nonglucose carbon sources

The gpd-promoter-controlled exocellular production of glucose oxidase (COD) by recombinant Aspergillus niger NRRL-3(COD3-18) during growth on glucose and nonglucose carbon sources was investigated. Screening of various carbon substrates in shake-flask cultures revealed that exocellular GOD activitie s were not only obtained on glucose but also during growth on mannose, fruc tose, and xylose. The performance of A. niger NRRL-3 (GOD3-18) using glucos e, fructose, or xylose as carbon substrate was compared in more detail in b ioreactor cultures. These studies revealed that gpdA-promoter-controlled GO D synthesis was strictly coupled to cell growth. The gpdA-promoter was most active during growth on glucose. However, the unfavorable rapid GOD-cataly zed transformation of glucose into gluconic acid, a carbon source not suppo rting further cell growth and GOD production, resulted in low biomass yield s and, therefore, reduced the advantageous properties of glucose. The total (endo- and exocellular) specific COD activities were lowest when growth oc curred on fructose (only a third of the activity that was obtained on gluco se), whereas utilization of xylose resulted in total specific GOD activitie s nearly as high as reached during growth on glucose. Also, the portion of GOD excreted into the culture fluid reached similar high levels (congruent to 90%) by using either glucose or xylose as substrate, whereas growth on f ructose resulted in a more pelleted morphology with more than half the tota l COD activity retained in the fungal biomass. Finally, growth on xylose re sulted in the highest biomass yield and, consequently, the highest total vo lumetric GOD activity. The results show that xylose is the most favorable c arbon substrate for gpdA-promotor-controlled production of exocellular GOD.