Enhanced porcine circovirus Cap protein production by Pichia pastoris with a fuzzy logic DO control based methanol/sorbitol co-feeding induction strategy

• Efficient porcine circovirus Cap protein production.
• Fuzzy logical DO control to automatically regulate methanol/sorbitol feeding.
• Improving foreign protein production by P. pastoris with strong AOX promoter.
• Restricting methanol consumption at moderately high level.
• Stabilizing DO control under mild air-aeration condition.

Porcine circovirus Cap protein production by P. pastoris with strong AOX promoter suffered with the problems with traditional pure methanol induction: (1) inefficient methanol metabolism; (2) extensive oxygen supply load; (3) difficulty in stable DO control; (4) low protein titer. In this study, based on the difference of DO change patterns in response to methanol and sorbitol additions, a novel fuzzy control system was proposed to automatically regulate the co-feeding rates of methanol and sorbitol for efficient Cap protein induction. With aid of the proposed control system when setting DO control level at 10%, overall fermentation performance was significantly improved: (1) DO could be stably controlled under mild aeration condition; (2) methanol consumption rate could be restricted at moderate level and the major enzymes involved with methanol metabolism were largely activated; (3) Cap protein concentration reached a highest level of 198 mg/L, which was about 64% increase over the best one using the pure methanol induction strategies.