DuPont Nutrition & Biosciences - When ‘Best-of-Both’ Traits Shine

The new glucoamylase-expressing yeasts within DuPont’s SYNERXIA® Gemstone Collection are both high yielding and fundamentally robust.
By Tom Bryan | December 28, 2020

Both nature and physics rarely allow two desired but incompatible outcomes to occur in unison—like chasing optimal efficiency with maximum output—and, because of it, ethanol production is full of difficult tradeoffs. “Best-of-both” scenarios are infrequent in biological processes; when one goal is met, another is often partially forfeited.  

Until recently, high-yield, glucoamylase (GA)-expressing yeasts were subject to precisely that type of limitation. Producers in search of the highest yielding yeasts had to sacrifice some degree of robustness. Those seeking the pinnacle of robustness had to give up some degree of yield.

Now, scientists are producing those dual traits, jointly, with more success. DuPont Nutrition & Biosciences, building on years of success with its high-yield, GA-expressing yeasts, is making the previously divergent characteristics of high yield and superior robustness—packaged together—a reality.  

“What we’ve seen in this industry is that you’re either going after yield or robustness,” says Lee Robinson, an application scientist at DuPont’s Applied Innovation Center in Cedar Rapids, Iowa. “There wasn’t much of a middle ground. The line between yield and robustness had to be walked with known consequences: engineering yeasts for yield came at the expense of robustness, and vice versa. But our newest line of yeasts from the XCELIS® platform, the SYNERXIA® Gemstone Collection, is changing that by creating a best-in-class combination of both yield and robustness.”

Robinson says DuPont began its latest journey to develop new yeasts with “good base genetics” that allowed its scientists to drive more robustness into the SYNERXIA® Gemstone Collection. “That’s where we really pushed hard,” he says. “We leveraged a set of very diverse genetic yeast backgrounds, and by mating our current high-yield yeast with an exceptionally robust yeast, we produced hybrid yeast strains with incredible genetic diversity.”

The resultant yeasts were then screened for performance under various stress conditions such as temperature and organic acid tolerance—“the type of stresses they would see at an ethanol plant,” Robinson says. “And after applying that stress and seeing what resulted, we were able to pick two winners.”

The selected pair of champion yeasts reside within a “best-of-both-worlds spectrum,” Robinson says, explaining that they are both high yielding and fundamentally robust. “We made sure we weren’t sacrificing either quality.”  

The new yeasts within DuPont’s SYNERXIA® Gemstone Collection—SYNERXIA® RUBY and SYNERXIA® SAPPHIRE—are both available in dry and cream formats. While the two yeasts vary in their makeup and overall attributes, both have enhanced temperature and organic acid tolerance, along with GA-expression that dramatically reduces the need for additional glucoamylase.

When GA-expressing yeast are employed, very little stand-alone glucoamylase needs to be added to the process during saccharification. In fact, Robinson says, SYNERXIA® RUBY results in a 65% reduction in GA (relative to conventional yeast dosage) and SYNERXIA® SAPPHIRE results in an 80% reduction.

“With  SYNERXIA® RUBY, which has DuPont’s patented high-yield, glycerol-reducing PKL pathway, we’ve also applied some additional, targeted genetic modifications that further enhance yield and provide an increase in robustness relative to its predecessor, SYNERXIA® THRIVE GX,” Robinson says. “So, the result is that  SYNERXIA® RUBY is our highest-yielding yeast to date from the XCELIS® platform.”

SYNERXIA® SAPPHIRE is intended to fulfill a different but equally important customer need. “Where SYNERXIA® RUBY is for ethanol producers focused on the highest-yielding yeast possible, SYNERXIA® SAPPHIRE is best suited for customers that want significantly more yield than a conventional yeast but also superior robustness,” Robinson explains. “SYNERXIA® SAPPHIRE gives you assurance that you’re going to survive and thrive during the upsets that inevitably occur.”

Unlike SYNERXIA® RUBY, SYNERXIA® SAPPHIRE does not have the patented PKL pathway built into it, but contains many other yield-enhancing modifications. Furthermore, SYNERXIA® SAPPHIRE and SYNERXIA® RUBY do not share the same GA. “The glucoamylase in SYNERXIA® RUBY is similar to its predecessor, but SYNERXIA® SAPPHIRE has a new glucoamylase that has the potential to lower residual starch in fermentation with an enhanced ability to reduce the need for additional GA—and that’s how we get to an 80% reduction.”

Both products have gone through extensive plant trials, despite the unique challenges of doing so during the pandemic. “We have excellent data sets from multiple plants,” Robinson says. “Whenever you trial new yeasts, you’re never quite sure what will emerge, but we saw  unique value in each yeast, and enough of a market segment for each product, to bring both of them forward together.”