An economical 20litre 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 °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 (OD600) of 30–32, compared with OD600 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 2.5 mg/litre/day achieved in shake flasks. The fermenter may be particularly suited for research purposes.