(785e) Microbial Synthesis of Plant Monolignols

Monolignols are direct precursors of lignin biosynthesis. Their derivatives also exhibit anti-oxidative, anticancer and canceroprotective activities. To achieve efficient production of the simplest monolignol p-coumaryl alcohol, four heterologous enzymes with high catalytic activities were selected for pathway construction. The full pathway was divided into the upstream and downstream partial pathways. Bioconversion study showed that the downstream enzymes were able to efficiently convert the phenylpropionic acids into the corresponding monolignols. E. coli strain containing the full pathway produced 501.8 ± 41.4 mg/L of p-coumaryl alcohol under optimized conditions. However, when the pathway was extended for the production of caffeyl alcohol, coniferyl alcohol, the promiscuity of the hydroxylase HpaBC led to the production of an instable intermediate L-dopa from tyrosine. In vivo and in vitro studies demonstrated that E. coli cell membrane provided a selective barrier toward tyrosine. Based on this, microbial co-cultures were designed. With the optimal inoculum ratio, 401.0 ± 15.3 mg/L of caffeyl alcohol was produced, which is nearly 12 times higher than that of the mono-culture. The same strategy was used for coniferyl alcohol production. Limited by the activity of methyltransferases, the highest titer was 124.9 ± 5.1 mg/L with 232.9 ± 15.1 mg/L of caffeyl alcohol accumulated. In this work, we achieved microbial production of three monolignols. This work also demonstrated the promising potential of microbial co-cultures for prevention of side-reactions.