Production of recombinant protein by a novel oxygen-induced system in Escherichia coli

The SoxRS regulon of E. coli is activated in response to elevated dissolved oxygen concentrations (dO₂). The soxS expression can be increased up to 16 fold, making it a possible candidate for recombinant protein expression. Compared with the existing induction approaches the oxygen induction offers several advantages: it does not involve addition or depletion of growth factors or nutrients, addition of chemical inducers or temperature changes that can affect growth and metabolism of the producing bacteria, it does not affect the growth-media composition simplifying the recovery and purification processes.

The soxS promoter was cloned into the pGFPmut3.1 plasmid creating pAB49, an expression vector that can be induced by increasing oxygen concentration. The efficiency and the regulatory properties of soxS promoter were characterized by measuring the GFP expression when the dO₂ in the culture was increased from 30% to 300% air saturation. The expression level of recombinant GFP was proportional to the dO₂, demonstrating that pAB49 is a controllable vector. Potentially harmful effect of oxygen on the GFP was found negligible as determined by protein-carbonyl content and specific activity. 

Performing high density growth the cells were induced by increasing the dO₂, after 3 hours at 300% air saturation, GFP fluorescence reached 109000 FU (494 mg of GFP/L) representing 3.4% of total protein.

In conclusion, the production of recombinant protein by increasing the dO₂ was found to be a tight and simple alternative expressing strategy that excludes the drawbacks of use of chemical, nutrient or thermal inducers.