Time: 15:30, Dec. 17, 2015

Venue: Room 506, Museum for Aquatic Organisms

Speaker: Yong Xue, National Center for Toxicological Research, FDA 

Title: Heterologous Production of Plant Secondary Metabolites p-coumaric Acid and Caffeic Acid in Synechocystis sp.PCC 6803  

Introduction to the Lecture:   

Caffeic acid, and its precursor p-coumaric acid, exhibit strong anticancer activities, and are natural phenolic compounds found in small amounts in plants. Production of caffeic acid by bacterial systems is technically challenging due to difficulties in functionally expressing ρ-coumarate 3- hydroxylase (C3H), a cytochrome P450 enzyme that converts ρ-coumaric acid into caffeic acid. Because of their photosynthetic ability and biosynthetic versatility, cyanobacteria are promising candidates for the production of certain plant metabolites.

Here, we produced p-coumaric acid in a novel transgenic cyanobacterium Synechocystis sp. PCC 6803 strain. Whereas a strain of Synechocystis 6803 genetically engineered to express sam8, a tyrosine ammonia lyase gene from the actinomycete Saccharothrix espanaensis, accumulated little or no p-coumaric acid, a strain that both expressed sam8 and lacked slr1573, a native hypothetical gene shown here to encode a laccase that oxidizes polyphenols, produced ~ 82.6 mg/L p-coumaric acid, which was readily purified from the growth medium.

Additionally, we report for the first time that the cyanobacterium Synechocystis PCC 6803 is able to produce caffeic acid from ρ-coumaric acid upon heterologous expression of C3H. The Arabidopsis thaliana ref8 gene, which encodes a C3H, was synthesized and codon-optimized for enhanced expression in Synechocystis. Expression of the synthetic ref8 gene was driven by a native psbA2 promoter and confirmed at the transcriptional and translational levels. This heterologous pathway enabled Synechocystis to produce caffeic acid at a concentration of ~7.2 mg L-1 from ρ-coumaric acid, and the yield was further increased to 72.4 mg/L upon deletion of slr1573. This work demonstrates that cyanobacteria are well suited for the bioproduction of plant secondary metabolites that are difficult to produce in other bacterial systems.