The MICA system

we developed the Metabolizable Inducer–based Carbon-source Autoinduction (MICA) system, which leverages six endogenous, inexpensive, non-toxic, and metabolizable carbon-source responsive regulatory modules in B. subtilis—maltose, mannose, sorbitol, arabinose, xylose, and glycerol. First, systematic engineering of key promoter elements substantially enhanced the expression strengths of all six regulatory modules. Second, integration with T7 RNA polymerase further amplified their output capacities, increased induction sensitivity, and reduced inducer consumption. Third, by exploiting glucose-mediated carbon catabolite regulation, each system was endowed with programmable autoinduction behavior, enabling induction at tunable time points through simple adjustment of glucose concentrations. Finally, the MICA system was applied to high-level production of alkaline protease and glucanase, as well as dynamic regulation of lycopene and β-carotene biosynthesis. Notably, the best-performing MICA module P_T7malA1 produced 82.54 mg L⁻¹ lycopene (4.50-fold higher than P_grac) and 94.25 mg L⁻¹ β-carotene (6.31-fold improvement than P_grac). The β-carotene titer achieved by P_T7malA1 is also the highest reported in B. subtilis to date. Collectively, the MICA system provides a versatile, low-cost, and non-toxic platform for robust protein overexpression and dynamic metabolic regulation, offering strong potential for scalable industrial biotechnology applications.