Temperature-regulated expression of the tac/lacI system for overproduction of a fungal xylanase in Escherichia coli

 Temperature-regulated expression of recombinant proteins in the tac promoter (P_tac) system was investigated. Expression levels of fungal xylanase and cellulase from N. patriciarum in E. coli strains containing the natural lacI gene under the control of the P_tac markedly increased with increasing cultivation temperature in the absence of a chemical inducer. The specific activities (units per milligram protein of crude enzyme) of the fungal xylanase and cellulase produced from recombinant E. coli strain pop2136 grown at 42°C were about 4.5 times higher than those of the cells grown at 23°C and were even slightly higher when compared with cells grown in the presence of the inducer isopropyl β-D-thiogalactopyranoside. The xylanase expression level in the temperature-regulated P_tac system was about 35% of total cellular protein. However, this system can not be applied to E. coli strains containing lacI ^q, which confers over production of the lac repressor, for high-level expression of recombinant proteins. In comparison with the λP_L system, the P_tac-based xylanase plasmid in E. coli pop2136 gave a considerably higher specific activity of the xylanase than did the best λP_L-based construct using the same thermal induction procedure. The high-level expression of the xylanase using the temperature-regulated P_tac system was also obtained in 10-litre fermentation studies using a fed-batch process. These results unambiguously demonstrated that the temperature-modulated P_tac system can be used for overproduction of some non-toxic recombinant proteins. Received: 27 June 1995/Received revision: 13 September 1995/Accepted: 30 September 1995