Efficient secretion of the model antigen M6-gp41E in Lactobacillus plantarum NCIMB 8826

Four Lactobacillus strains (Lb. plantarum NCIMB 8826, Lb. paracasei LbTGS1.4, Lb. casei ATCC 393 and Lb. fermentum KLD) were tested for their ability to produce and secrete heterologous proteins. These strains were first screened with an alpha-amylase reporter under the control of a set of expression or expression/secretion signals from various lactic acid bacteria. With most of the constructions tested, the level of extracellular production was highest in Lb. plantarum NCIMB 8826, and lowest in Lb. paracasei LbTGS1.4. These two strains were next assayed using a model antigen consisting of the N-terminal part of the M6 protein from Streptococcus pyogenes fused to the linear epitope ELDKWAS from human immunodeficiency virus gp41 protein. Secretion of this heterologous protein was inefficient in Lb. paracasei LbTGS1.4, which accumulated a large intracellular pool of the unprocessed precursor, whereas Lb. plantarum NCIMB 8826 was able to secrete the antigen to a level as high as 10 mg l-1.