New Strand of E. coli Helps Instead of Hurts

By Mike Howie

For most of us, E. coli is most closely associated with the negative consequences of eating food or drinking water that wasn’t exactly clean. However, most varieties of the bacteria live harmlessly in the intestines of healthy humans and animals. And now researchers from the Novo Nordisk Foundation Center for Biosustainability at the Technical University of Denmark (DTU) have found another use for it: producing a moisturizer for lotions and an ingredient for a range of other products.

Serine is one of the 20 amino acids that form proteins in the human body, and it’s used for much more than just producing cosmetics. In the body, serine is important in maintaining health, preventing disease and developing the brain and its functions, and it’s necessary for specific central nervous system functions. Elsewhere, serine is used in detergents and tube feeding formula, it’s a building block for a number of important chemicals, and it's one of the 30 most promising biological substances that can be used to replace chemicals from the oil industry. In the chemicals industry alone serine can be converted into plastics, dietary supplements and a variety of other products.

A Cheaper Solution

With so many uses for serine, finding a way to sustainably produce large quantities of it at a low cost is a big deal. The current production process uses microbes, which must first be grown in large quantities, to convert methanol and glycine (the latter of which is relatively expensive) into serine. But that’s neither quick nor easy. Other amino acids are produced through bacterial fermentation using E. coli — a common laboratory workhorse — but serine is toxic to E. coli. That’s where the researchers at DTU come in: They’ve created a strain of E. coli that can not only survive in large concentrations of serine but also produces record amounts of the substance.

Their first challenge was acclimating E. coli cells to living with serine. The researchers used Adaptive Laboratory Evolution (ALE) to do this: They selected cells that were best suited to tolerate serine and slowly introduced them to higher and higher concentrations of it. 

That may sound simple, but the cells had to be constantly monitored and transferred from one medium to the next at specific times during their growth — a task that would be nearly impossible to perform by hand. To get it right, the team used specialized ALE robots that are unique to their facilities in Denmark and the United States. The resulting serine-tolerant cells were then genetically optimized to produce serine, and were found to produce 250 to 300 grams of the substance per kilogram of glucose added — the largest productivity for serine ever achieved. They’ve also seen promising results when using residues from sugar production, like molasses, and other less expensive sugars. In short, they can make a lot of serine with little expense.

Once implemented on a large scale, this new production method will make serine and serine-containing products more affordable. The researchers are already planning to establish a company that will further develop their work, produce large quantities of serine, and commercialize their results.