Currently available protein production platforms are not suited for the biosynthesis of unstable or cytotoxic proteins. We have created a new platform, based on B. thuringiensis (Bt), to overproduce proteins stored in crystals. When in crystals, proteins are densely packed in an ordered way that highly decreases their intramolecular motion and limits the exchanges with the surrounding milieu. Thus, proteins and their host cells are protected and production of unstable or cytotoxic proteins, a lengthy, costly and tedious process, is much facilitated. In addition, crystals greatly facilitate the purification of the protein of interest, and represent a means to slowly release it in the surrounding milieu. Bt is a sporulating bacterium largely used in crop protection because of its massive production of insecticidal Cry proteins, stored in large crystalline parasporal bodies. We have used Bt molecular tools to implement, in a non-sporulating mutant (ghost cell), the two main pathways leading to protein overproduction and crystallization. One pathway used the large cysteine-rich C-terminal domain of Cry toxins, fused to the protein of interest, while the other relied on a so-called helper protein thought to work as chaperone. In both strategies, GFP used as a proof of concept was stored in fluorescent crystals, where it represented up to 60% of total protein. The quantity of GFP produced in presence of a helper protein was greatly enhanced in comparison with the control without it, indicating that protein stability was significantly improved in crystals.