An economical 20 litre bench-top fermenter

We describe an economical 20 litre bench-top fermenter suitable for production of recombinant antibody fragments in bacterial expression systems. The bacterial culture contained within a polycarbonate carboy is mixed (400-600 rpm) and aerated (1 vessel vol./min) by a high-shear radial flow impeller mounted on a hollow stainless steel shaft, through which pressurised air is pumped. Air is dispersed as fine bubbles into the culture medium by the turbine impeller, without the need for a porous sparger. A stainless steel baffle stabilised by a gliding counterweight increases mixing. The components can easily be disassembled for cleaning and sterilisation. Temperature (range 20-37 degrees C) and pH (range 7.0-7.5) are controlled manually. Using the apparatus, it proved possible to achieve Escherichia coli cell culture densities equivalent to an optical density at 600 nm (OD(600)) of 30-32, compared with OD(600) 4-6 in shake flasks. A yield of 40 mg/litre/day of a recombinant antibody fragment was obtained with the fermenter, which was 15-fold more than the yield of 2.5mg/litre/day achieved in shake flasks. The fermenter may be particularly suited for research purposes.