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Using lactose as an inducer, recombinant human interleukin-2 (rhIL-2) was synthesized with an N-terminus fusion partner, G3 (three tandem-arranged glucagon peptides) in fed-batch cultures at high cell concentration (60–90 g l−1) of Escherichia coli BL21(DE3) [pT7-G3IL2]. With batch additions of lactose (4 × 13.5 g), the fusion rhIL-2 was synthesized up to 9.3 g l−1. However, if all the lactose (54 g) was added at once to the culture, synthesized fusion rhIL-2 decreased to 5.4 g l−1 with a decreased cell growth rate. A statistical optimization of the production medium containing glucose, yeast extract, and lactose led to fusion rhIL-2 being produced at > 9 g l−1.

A bioreactor system equipped with a hollow fiber cross-filtration module was used for continuous cultivation of Lactobacillus acidophilus at high cell concentrations. The growth rate did not correlate with the lactate concentration if the residual glucose concentration was kept nearly zero in the culture broth. To achieve this, an effective control method of medium feed rate was developed on the basis of the correlation between the specific glucose consumption rate (nu) and the specific cell growth rate (mu), i.e. nu = 52.90 mu + 0.39. Growth up to 50 g dry wt l-1 was achieved without glucose accumulation under the total cell recycle. Via the partial cell recycle, continuous biomass production was achieved with a steady-state L. acidophilus concentration and dilution rate being 40 gl-1 and 0.09 h-1. © Rapid Science Ltd. 1998

The recombinant human granulocyte-colony-stimulating factor (rhG-CSF) was synthesized in a fusion protein using a GAL1-10 UAS in recombinant Saccharomyces cerevisiae and the intracellular KEX2 cleavage led excretion of mature rhG-CSF into the extracellular culture broth. The recombinant yeast growth in fed-batch cultures was controlled by precise computer-aided medium feed. The optimal C/N ratio in preinduction (glucose/Casamino acids) and post-induction (galactose/yeast extract) feed media was determined at 3 and 2, respectively. The final rhG-CSF and cell concentration was more than 60 mg/L and 70 g/L, respectively, with around 90% plasmid stability and negligible ethanol accumulation. Comparing the cell growth between the hG-CSF + and hG-CSF - recombinant strains shows that the cloned gene product does not hamper the host cell growth.

Using cell recycle, the concentration of M. trichosporium OB3b was increased to more than 12g/L in continuous culture and biomass productivity was enhanced up to 0.708g/L/h. The optimal temperature and pH for soluble MMO activity were 35°C and 6.2–6.4. The Optimal concentrations of methanol and sodium formate, as cofactor regenerators, were 0.5mM and 10 mM, respectively, at which the soluble MMO activity was about 8 times enhanced.

The steady-state concentration of M. trichosporium OB3b increased about two-fold in the continuous culture when the feeding medium was supplemented by ferrous sulphate (50mg/L) and citric acid (100mg/L) at a steady state. In batch and continuous cultures, the cell growth was significantly inhibited by excess N-sources (NH4OH, NH4Cl, NH4NO3, HNO3, and NaNO3) and ammonium N-sources were more inhibitory. Both volumetric O2 transfer coefficient and specific O2 uptake rate increased monotonously in an extensive range of air flow rate (0.1–7 vvm) and the methane interfered with the O2 transfer even at very low flow rates (0.01–0.1 vvm).