Enhancement of extracellular pullulanase production from recombinant Escherichia coli by combined strategy involving auto-induction and temperature control.

Pullulanase was extracellularly produced with an engineered Escherichia coli with a combined strategy. When auto-induction instead of isopropyl β-D-1-thiogalactopyranoside (IPTG) induction method was implemented, we observed increased extracellular activity (4.2 U ml(-1)) and cell biomass (7.95 g DCW l(-1)). Subsequent investigation of temperature effect on fermentation showed cultivation performed at 25 °C presented the highest extracellular titer and cell biomass. In order to reduce the extended production period, we developed a two-stage temperature control strategy. Its application not only reduced the production period from 72 to 36 h, but also further enhanced the yield of extracellular pullulanase. Finally, with a view to releasing more intracellular pullulanase, we altered cell membrane permeability with various medium additives. As a result, extracellular titer was elevated to 68.23 U ml(-1), nearly 35-fold higher than that with IPTG induction method. The combined strategy developed here may be useful for the production of other extracellular proteins by recombinant E. coli.