Feeding strategy design for recombinant human growth hormone production by Bacillus subtilis

Defined and semi-defined medium-based feeding strategies were developed to enhance recombinant human growth hormone (rhGH) production by Bacillus subtilis BGSC-1A178 (scoC ⁻) strain carrying pMK4::pre(subC)::hGH. Defined medium-based feeding strategies were designed by exponential feeding of glucose and (NH₄)₂HPO₄ at two pre-determined specific growth rates, µ ₀ = 0.10 and 0.17 h⁻¹. Semi-defined medium-based feeding strategies were designed by exponential feeding of substrate solution consisting of glucose, (NH₄)₂HPO₄, peptone, and trace salt solution (PTM1) at three pre-determined specific growth rates, µ ₀ = 0.10, 0.17, and 0.25 h⁻¹. At all the strategies applied, transition cultivation time from batch to fed-batch operation was t T = 4 h. The highest rhGH concentration was obtained as C ᵣₕGH = 0.5 g L⁻¹ with semi-defined medium-based feeding strategy designed with µ ₀ = 0.25 h⁻¹ using feed substrate stock solution containing 200 g L⁻¹ glucose, 117 g L⁻¹ (NH₄)₂HPO₄, 100 g L⁻¹ peptone, and 5 mL L⁻¹ PTM1 at t = 22 h when the cell concentration reached to C X = 8.29 g L⁻¹. The overall product and cell yields on glucose were obtained as [Formula: see text] = 7.21 mg g⁻¹ and [Formula: see text] = 0.12 g g⁻¹, respectively. The results indicate the requirement of designing continuous feed stream in fed-batch production to enhance rhGH production by r-B. subtilis.