Engineering chlorophyll, bacteriochlorophyll, and carotenoid biosynthetic pathways in Escherichia coli

The biosynthesis of chlorophylls (Chls) and bacteriochlorophylls (BChls) represents a key aspect of photosynthesis research. Our previous work assembled the complete pathway for the synthesis of Chl a in Escherichia coli; here we engineer the more complex BChl a pathway in the same heterotrophic host. Coexpression of 18 genes enabled E. coli to produce BChl a, verifying that we have identified the minimum set of genes for the BChl a biosynthesis pathway. The protochlorophyllide reduction step was mediated by the bchNBL genes, and this same module was used to modify the Chl a pathway previously constructed in E. coli, eliminating the need for the light-dependent protochlorophyllide reductase. Furthermore, we demonstrate the feasibility of synthesizing more than one family of photosynthetic pigments in one host by engineering E. coli strains that accumulate the carotenoids neurosporene and β-carotene in addition to BChl a.