Microbial Production of Crocins: Enzymes, Pathways, and Engineering Strategies

Crocins are highly valuable apocarotenoids with important applications in the food industry. Currently, crocin production primarily relies on complex plant extraction, which is labor-intensive and yields products of low purity. The elucidation of the crocin biosynthetic pathway has opened new opportunities for large-scale production of crocins through synthetic biology and metabolic engineering. However, efficient production of crocins by heterologous hosts is still challenging due to their complicated biosynthetic pathway and the low efficiency of pathway enzymes. In this paper, we comprehensively review the research advances in engineering heterologous hosts for crocin biosynthesis, with particular emphasis on enzyme characterization and pathway engineering. Finally, we discuss the challenges hindering efficient microbial production of crocins and highlight potential strategies for developing robust crocin-producing microbial cell factories from the perspectives of synthetic biology and metabolic engineering.