Extracellular Expression of a RecombinantGanoderma lucidiumImmunomodulatory Protein by Food-GradeLactococcus lactisSystem

Lactococcus lactis is a food-grade microorganism of major commercial importance in food industry. For commercial application of genetically modified L. lactis, a food-grade expression system is strongly recommended. In this study, two food-grade selection markers, nisin immunity gene nisI and nisin resistance gene nsr, were evaluated as dominant markers for the L. lactis food-grade expression system. By using an efficient PSlpAl promoter fused to a signal peptide from subtilisin YaB (SPYAB), a functional recombinant Ganoderma lucidium immunomodulatory protein rLZ8 was expressed extracellularly in L. lactis. Replacing the antibiotic marker gene into the proper food-grade selection marker nsr gene, the rLZ8 was expressed extracellularly in the food-grade L. lactis system. This study provides a rationale basis for a food-grade system to express functional peptides extracellularly as an important tool for oral administration of genetically modified L. lactis.