Fermentation can be used to produce vitamins, proteins, food ingredients such as dyes and flavors, medicines and vaccines. Credit: DTU
The growing world population means that the environment is under great strain. Agriculture takes up large land areas and discharges nutrients to the surrounding environment. At the same time, there is tremendous pressure on the aquatic environment from all forms of industrial production that emits residual products such as wastewater, and regardless of whether we are talking about agricultural operations or industry, it is today associated with a huge energy consumption and the resulting climate impact.
With a new research breakthrough, researchers from DTU have succeeded in tackling all these problems in their search for the food of the future. Using the yeast cell Debaryomyces hansenii (D. hansenii), the researchers have shown that it is possible to exploit some of the industry's problematic waste streams to produce proteins at very low cost and very low energy consumption. This could move food production away from the fields and into steel tanks, the environment is spared from the wastewater, and the climate is far less impacted by CO2.
Salt-tolerant yeast
For many years, Associate Professor José Martinez from DTU Bioengineering has researched yeast cells that in nature are adapted to extreme conditions such as high temperatures, low nutrient content, or high salinity. D. hansenii is adapted to aquatic environments with high salinity and thrives in water up to six times as salty as normal seawater. That gave the associate professor an idea.
"There are businesses that create waste streams that are rich in nutrients, but also have a very high salt content, which is often a problem. The salinity prevents utilization of the nutrients while preventing businesses from discharging their waste streams as ordinary wastewater, which means they have to special treat, and this is costly. Why don't we try to grow this type of yeast in these salty waste streams?" he asked himself.
Sugar and nitrogen
José and his research team therefore contacted Arla Foods and agreed to test D. hansenii in a highly salty residue from cheese production—a residue that was also rich in the sugar lactose. The experiment exceeded all expectations. The yeast cells easily metabolized the sugars from this waste stream, and the higher the salt content, the more efficient the growth. However, the yeast growth was not quite as efficient as it could be. There was simply too little nitrogen present.
Manuel Quirós works as a specialist at Novo Nordisk and, like Martinez, has researched the yeast type D. hansenii. During a coffee meeting, the two biologists discussed the limitations of the DTU researcher's results with the lactose-rich waste stream. Quirós said that Novo Nordisk ends up with a salty residue that is high in nitrogen in connection with the manufacture of hemophiliacs, and thought that it might be useful. And it quickly developed from a coffee talk to an experimental setup.
"We simply mixed the two saline waste streams—the one with a high lactose content and the one with a high nitrogen content. We used them as they were. We didn't need to add fresh water, nor did we need to sterilize the fermentation tank, because the salt prevented the growth of other microorganisms. It was plug and play," as the associate professor puts it.
D. hansenii thrived in this salty mixture. But if it was to be of more than research interest, then the yeast would also have to produce a commercially interesting product, and with the help of the gene technology CRISPR, Martinez's research team modified D. hansenii to form a protein as it grew.
Provided by Technical University of Denmark