Engineering Lactococcus lactis as a Cell Factory for the Production of Limonene

Limonene is a plant monoterpene which contributes significantly to the scent of most essential oils due to its pleasant fragrance. The compound had been reported to have anti-cancer properties against several types of cancer including colorectal cancer. However, the production of this compound in nature is limited because it is produced as a secondary metabolite. To overcome these challenges, Lactococcus lactis was developed as a heterologous host for the production of limonene. A synthesized limonene synthase (LS) from Mentha spicata (mint) was cloned into L. lactis NZ9000. Western blot analysis using mouse IgG His-Tag monoclonal antibody showed successful LS expression by L. lactis at the size of similar to 55 kDa. GC-MS analysis results showed that limonene production was optimum after 24 h of induction (similar to 8.0 ppm). Metabolic engineering was attempted to enhance the limonene production by overexpression of lactococcal 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and mevalonate kinase (mvk) genes in the bacterial host. The recombinant L. lactis carrying pNZ:ISMM plasmid successfully enhanced the limonene production to two fold (similar to 15.1 ppm) after 24 h of induction. The outcomes of this study show the potential of L. lactis to produce plant proteins and bioactive compounds production, which prospectively leads to an oral delivery system for anti-cancer compounds.