Medium optimization and production of secreted Renilla luciferase in Bacillus subtilis by fed-batch fermentation

Luciferase of the soft coral Renilla reniformis (Rluc) has found a multitude of potential applications. However, its production in a secreted form has been solely performed in mammalian cells. In this work, a high production of secreted Rluc was approached in Bacillus subtilis by implementing the fermentation strategy. First, three critical medium components among others were selected by the Plackett–Burman design. Followed by the Box–Behnken design, the medium formulation was optimized and composed of 1.17% glucose, 2.27% yeast extract, and 0.55% glutamate. With the optimum medium, the shake-flask culture of the producer strain was carried out to secret Rluc with the yield of 55 mg/L. Finally, the production scheme was scaled up using a 5-L jar fermenter operated in a fed-batch mode. By controlling the operational condition, the feeding solution was pumped in an impulse mode to the culture. As a consequence, the production of Rluc reaching 500 mg/L was obtained after fermentation for 27 h.