Characterization of Zymomonas mobilis promoters that are functional in Escherichia coli

Zymomonas mobilis ZM4 is a gram-negative, facultative anaerobic, natural ethanologenic bacterium used in industrial production of bio-products. For expression of genes, promoters are required. However, most of the promoters reported from Z. mobilis poorly function in Escherichia coli. This makes the process of expression and screening labor-intensive. In the present study, we compared the strengths of two Z. mobilis promoters, Pchap and Ppap, which drive the expression of chaperonin and phosphatase PAP2 family protein, respectively, with Ptac promoter. In E. coli, the Ptac promoter was found to be the strongest followed by Ppap and Ppdc, while in Z. mobilis, Ppdc was found to be the strongest and Pchap the weakest promoter. Further characterization of the promoters was done by cloning the gfp_uv gene which expresses the green fluorescent protein, under their control and measuring the fluorescence of the E. coli transformants. The activity of these promoters was also studied at different pH (pH 5, 7 and 9) and different temperatures (30°C, 37°C and 42°C) in exponential and stationary phases. Both Pchap and Ppap promoters showed higher activity in stationary phase than in exponential phase. Since the promoters were active at all temperatures and pH studied, they can be used for gene expression in E. coli under desired environmental conditions.