Genetically engineered Blue silkworm capable of synthesizing natural blue pigment

Synthetic biology is an eco-friendly and sustainable approach for the production of compounds, particularly used when the production processes involve toxic reagents. In this study, we used the silk gland of silkworm to produce indigoidine, a valuable natural blue pigment that cannot be synthesized naturally in animals. We genetically engineered these silkworms by integrating the indigoidine synthetase (idgS) gene from S. lavendulae and the PPTase (Sfp) gene from B. subtilis into the silkworm genome. In the resulting Blue silkworm, indigoidine was detected at a high level in the posterior silk gland (PSG), spanning all developmental stages from larvae to adults, without affecting silkworm growth or development. This synthesized indigoidine was secreted from the silk gland and subsequently stored in the fat body, with only a small fraction being excreted by the Malpighian tubule. Metabolomic analysis revealed that Blue silkworm efficiently synthesized indigoidine by upregulating l-glutamine, the precursor of indigoidine, and succinate, which is related to energy metabolism in the PSG. This study represents the first synthesis of indigoidine in an animal and therefore opens a new avenue for the biosynthesis of natural blue pigments and other valuable small molecules.