We observed that fusion of the LEISS propeptide and Nuc, as initially described in L. lactis, improved both BLG production and secretion in L. casei. Furthermore, integration of nisRK genes into the L. casei BL23 chromosome allowed to strengthen nisin-dependent production of BLG and led to higher yields of recombinant protein. As previously mentioned in L. lactis, all these modifications did not improve the proportion of soluble BLG in the intracellular fraction . Production of soluble BLG was nevertheless improved by performing nisin induction on L. casei cultures at higher cell density.
These recombinant strains were primarily designed to evaluate the potential advantages of using probiotic lactobacilli for the mucosal delivery of an antigen in a mouse model of allergy. This raised different questions such as whether we need in situ production and secretion of the antigen to induce or modulate an immune response or what is the most effective way of administration. In this regard, we are currently testing the BLG-producing L. casei for prophylactic and therapeutic treatments on mice, via delivery of recombinant lactobacilli by oral and intranasal administrations.