Tianjin University develops customized synthetic microbial cell factory

A team led by Zhao Guangrong, a professor of Tianjin University (TJU), established an artificial biosynthetic pathway to produce salvianic acid A in an engineered bacterial fermentation process. 

Results of the breakthrough were published in Metabolic Engineering and Microbial Cell Factories, two well renowned biotechnology journals. The invention patents were authorized by the State Intellectual Property Office of China. 

Salvianic acid A, a drug with the active pharmacological properties of improving cerebral blood flow, inhibiting platelet activation and arterial thrombosis, is used to treat cardiovascular diseases. Salvianic acid A is now prepared from the plant Salvia miltiorrhiza root, but has low yield and unreliable quality. 

Salvianic acid A is extracted from Salvia miltiorrhiza root in China. The traditional method of water extraction followed by alcohol precipitation led to excessive concentration of alcohol and loss of phenolic constituents including salvianic acid A. 

More recent preparation methods including enzymatic and microwave extraction have not resolved crucial problems such as limited plant material, unreliable quality and low productivity as well as the seasonal and geographical constraints of growing Salvia miltiorrhiza. 

Although full synthesis of the natural product is considered to improve the quantity and quality of the derived medical products, the chemical synthesis of salvianic acid A was troubled by complex procedures, poor stereoselectivity, low yield and was an unfriendly environmental impact. 

Professor Zhao's team developed the artificial biosynthesis of salvianic acid A. Guided by catalytic mechanisms of bio-enzymes and retrosynthetic analysis and by mining big bioinformation databases, the team discovered that a P450 enzyme can hydroxylate by meta-position hydroxyphenylpyruvic acid, the precursor of salvianic acid A. A D-lactic dehydrogenase can reduce keto in the hydroxyl group, which generates salvianic acid A. 

The team recombined and reassembled genetic modules for synthetizing hydroxyphenylpyruvic acid and attained Escherichia coli cells as chassis to mass produce the precursor. 

Then they introduced the module of salvianic acid A synthetic genes into the chassis cell, and established the artificial biosynthesis of salvianic acid A from glucose. The customized synthetic microbial cell factory produced salvianic acid A is above 7g/L.
Nature Chemical Biology, a Nature journal, highlighted the team's research and pointed out that "this artificial route provides a new source for a plant polyphenols". 

The team recently modified the genome by precisely integrating the genetic modules of biosynthetic salvianic acid A and the enhanced precursor supply onto a chromosome of Escherichia coli. Meanwhile, they deleted junk genes so that engineered Escherichia coli was more efficient as a microbial cell factory. Thus, salvianic acid A could be continually synthesized without additional use of antibiotics and fermentation inducers. 

The project was supported by the National Basic Research Program of China, the National High-Tech R&D Program of China, and the Natural Science Foundations of China and Tianjin. 

Nowadays, synthetic biology has become a powerful engine for the development of green bio-manufacturing. This next generation of biotechnology promises to solve major issues of resource and energy depletion, healthcare, the environment and security by reshaping the traditional biotech industry. Zhao's research is one excellent example of the customized production of medicines and valuable chemicals by decreasing dependency on natural resources.