Induction of gene expression in bacteria at optimal growth temperatures

Traditional temperature-sensitive systems use either heat shock (40-42 A degrees C) or cold shock (15-23 A degrees C) to induce gene expression at temperatures that are not the optimal temperature for host cell growth (37 A degrees C). This impacts the overall productivity and yield by disturbing cell growth and cellular metabolism. Here, we have developed a new system which controls gene expression in Escherichia coli at more permissive temperatures. The temperature-sensitive cI857-P (L) system and the classic lacI-P (lacO) system were connected in series to control the gene of interest. When the culture temperature was lowered, the thermolabile cI857 repressor was activated and blocked the expression of lacI from P (L). Subsequently, the decrease of LacI derepressed the expression of gene of interest from P (lacO) . Using a green fluorescent protein marker, we demonstrated that (1) gene expression was tightly regulated at 42 A degrees C and strongly induced by lowering temperature to 25-37 A degrees C; (2) different levels of gene expression can be induced by varying culture temperature; and (3) gene expression after induction was sustained until the end of the log phase. We then applied this system in the biosynthesis of acetoin and demonstrated that high yield and production could be achieved using temperature induction. The ability to express proteins at optimal growth temperatures without chemical inducers is advantageous for large-scale and industrial fermentations.