Comparison of expression vectors in Lactobacillus reuteri strains

Synthesis of heterologous proteins in lactobacilli is strongly influenced by the promoter selected for the expression. In addition, the activity of the promoters themselves may vary among different bacterial hosts. Three different promoters were investigated for their capability to drive EGFP expression in L. lactis spp. cremoris MG1363, in Lactobacillus reuteri DSM 20016T and in five Lactobacillus reuteri strains isolated from chicken crops. The promoters of L. acidophilus Surface Layer Protein gene (slp), L. acidophilus lactate dehydrogenase gene (ldhL) and enterococcal rRNA adenine N-6-methyltransferase gene (ermB) were fused to the coding sequence of EGFP and inserted into the backbone of pTRKH3 shuttle vector (pTRKH3-slpGFP, pTRKH3-ldhGFP, pTRKH3-ermGFP). Besides conventional analytical methods, a new quick fluorimetric approach was set up to quantify the EGFP fluorescence in transformed clones using the QubitTM fluorometer. ermB proved to be the most effective promoter in L. reuteri isolates producing 3.90 x 10-7 g of fluorescent EGFP (ml x ODstationary culture)-1. In the same conditions ldhL promoter produced 2.66 x 10-7 g of fluorescent EGFP (ml x ODstationary culture)-1. Even though the slp promoter was efficient in L. lactis spp. cremoris MG1363, it was nearly inactive both in L. reuteri DSM 20016T and in L. reuteri isolates.