Optimisation and scale-up of α-glucuronidase production by recombinant Saccharomyces cerevisiae in aerobic fed-batch culture with constant growth rate

• Critical specific growth rate of S. cerevisiae MH1000pbk10D-glu was 0.12 h−1.
• α-Glucuronidase production was closely correlated with biomass production.
• Maximum α-glucuronidase production occurred at the critical specific growth rate.
• Scale-up based on constant kLa was successfully applied.

α-Glucuronidase (EC 3.2.1.139) of family GH 115 from Scheffersomyces stipitis is a valuable enzyme for the modification of water-soluble xylan into insoluble biopolymers, due to its unique ability to act on polymeric xylans. The influence of growth rate on the production of α-glucuronidase by recombinant Saccharomyces cerevisiae MH1000pbk10D-glu in glucose-limited fed-batch culture was studied at 14 and 100 L scale. At and below the critical specific growth rate (μcrit) of 0.12 h−1 at 14 L scale, the biomass yield coefficient (Yx/s) remained constant at 0.4 g g−1 with no ethanol production, whereas ethanol yields relative to biomass (keth/x) of up to 0.54 g g−1 and a steady decrease in Yx/s were observed at μ > 0.12 h−1. Production of α-glucuronidase was growth associated at a product yield (kα-glu/x) of 0.45 mg g−1, with the highest biomass (37.35 g/L) and α-glucuronidase (14.03 mg/L) concentrations, were recorded during fed-batch culture at or near to μcrit. Scale-up with constant kLa from 14 to 100 L resulted in ethanol concentrations of up to 2.5 g/L at μ = 0.12 h−1. At this scale, α-glucuronidase yield could be maximised at growth rates below μcrit, to prevent localised high glucose concentration pockets at the feed entry zone that would induce oxido-reductive metabolism. This is the first report where recombinant production of α-glucuronidase (EC 3.2.1.139) by S. cerevisiae was optimised for application at pilot scale.