Scientists are now able to produce a wide range of sulfated aromatic compounds such as antifouling eelgrass acid, resveratrol and vanillic acid derivatives using microbial production hosts.
Leveraging on nature’s ways of adding sulfate groups by enzymes, scientists at The Novo Nordisk Foundation Center for Biosustainability at DTU have for the first time demonstrated how to produce a wide range of sulfated phenolic compounds in microbial hosts – cell factories. This pioneering research, published in Nature Communications, enables large scale production of sulfated phenolic compounds by fermentation.
“The perspectives are far-reaching since sulfation can be used for a wide range of products such as antifouling agents and pharmaceuticals. This work could mean cheaper and better drugs in the future as well as bio-chemicals and polymers with new properties”, says corresponding author Professor Alex Toftgaard Nielsen from The Novo Nordisk Foundation Center for Biosustainability at Technical University of Denmark (DTU). He is also CSO at Cysbio – a company that works to commercialize products from, amongst other things, sulfated molecules.
Phenolic compounds are aromatic molecules with uses in areas such as medicine, in nutraceuticals, as antioxidants, in the cosmetic industry as well as in the polymer industry. Adding sulfate residues to phenolic compounds can increase the acidity and solubility of the molecule as well as decreasing the toxicity.
Searched high and low – from eelgrass to rat
As a proof of concept for the sulfation process in cell factories, the researchers wanted to produce zosteric acid. This acid is found in the marina plant eelgrass and is a powerful antifouling agent. Used in ship paint, it could potentially inhibit the growth of algae on the hull. Furthermore, it has applications in disinfectants, where it can prevent the attachment of bacteria on surfaces (biofilms) e.g. in hospitals.
Today, zosteric acid can be extracted from plant material, but titers are low, and the cost is high. Zosteric acid may also be synthesized chemically, but this requires harsh chemical conditions and generates a lot of chemical waste. Thus, a biological process is preferable.
Biologically, zosteric acid is created by an enzyme (sulfotransferase) that transfers a sulfate side-group to a specific building block molecule. Therefore, the researchers isolated sulfotransferases from humans, fruit flies, eelgrass, rats, chickens, rabbits, dogs, worms, zebrafish, and pigs to find the most efficient one. The winner enzyme was actually isolated from rat liver and worked superbly in the microbial production host.
The researchers had to re-engineer and rewire several genes within the cell factory to optimize the sulfation process. This was both done by improving sulfate uptake and by optimizing the availability of the sulfate donor enzyme in the cell.
The result was the production of up to five grams per liter of zosteric acid in a so-called fed-batch fermentation. This yield is impressive since nature normally only produces zosteric acid in very low quantities, and because chemical synthesis is extremely difficult and expensive.