Food-grade gene transformation system constructed in Lactobacillus plantarum using a GlmS-encoding selection marker

Food-grade gene expression systems in lactic acid bacteria enable production of functional proteins or product testing without antibiotic requirement. Here, we expanded the available selection markers by developing a novel food-grade genetic transformation system for Lactobacillus plantarum WCFS1 using the glucosamine-6-phosphate synthase gene (glmS1). A glmS-vector pSIPH497 was constructed by replacing the erythromycin resistance gene (erm) with L. plantarum glmS1 under control of the PₗdₕL promoter from WCFS1. The selection efficiency and stability of the glmS-vector were shown to be comparable to those of the erm-based plasmid. Moreover, using mCherry expression as a reporter gene, we showed the feasibility of the system for producing foreign proteins. This food-grade host/vector system will provide an effective and safe technique for the application of lactic acid bacteria in the food and medical industries. Furthermore, this study provides a useful strategy for developing food-grade selection markers in other host/vector systems.