California-based Switch Bioworks has begun its first multi-state field trials in corn in the Midwest, testing engineered nitrogen fixing microbes designed to colonize plant roots before switching on ammonia production several weeks into the growing season.
The in-furrow trials, which began in May, mark the company’s move from lab and greenhouse work into what founder Tim Schnabel, PhD, described as the “ultimate test”: whether its microbes can survive, establish themselves and behave as programmed under variable field and soil conditions.
Switch deploys a mixture of nitrogen-fixing soil microbes that naturally produce an enzyme called nitrogenase that enables them to combine nitrogen with hydrogen to produce ammonia, enabling growers to reduce synthetic fertilizer use, Schnabel told AgFunderNews.
“The active compound [ammonia] the microbes are making is the exact same as Haber-Bosch [a heat- and energy-intensive industrial process], using enzymes that have the capacity to make it at room temperature, which is kind of a marvel of nature.”
Switch engineers its microbes to first compete with the native soil microbiome and establish themselves before a genetic switch turns on that triggers ammonia production, he explained.
“We have to upregulate the level of nitrogen fixation such that there’s an excess, because in nature microbes will only fix as much nitrogen as they need for themselves. And then we have to tell the microbe to share that nitrogen with the plants.”
Schnabel did not disclose the precise environmental trigger but noted that it responds to a change in the soil environment after several weeks and does not require any intervention on the part of farmers.
Field trials
During the trials, best described as “late-stage R&D trials” rather than demonstrations of a commercially ready fertilizer product, Switch is trying to answer three key questions, said Schnabel:
- Can the microbes establish and persist on corn roots?
- Does the genetic switch activate at the right time?
- Which microbes should form the eventual product?
The company is measuring the composition of the wider root microbial community, the relative abundance of its engineered strains, switch activation—detectable through a DNA-sequence change—plant nitrogen-response indicators and yield.
However, Switch is not necessarily expecting a measurable nitrogen or yield response this season. The immediate goals are colonization and correct switch timing, said Schnabel.
Why the switching mechanism matters
Nitrogen fixation imposes a heavy metabolic burden on microbes. According to Switch’s thesis, engineering microbes to produce large amounts of nitrogen continuously can make them less competitive against native soil organisms, meaning they may fail to establish themselves in sufficient numbers.
Switch is therefore separating the two jobs:
- First, the microbes compete, multiply and colonize the roots.
- Later, the genetic switch activates ammonia production and programs the microbes to produce more nitrogen than they require themselves and “share” it with corn plants.
Schnabel argued that this colonization–fitness trade-off is a key challenge for the broader microbial fertilizer industry and is Switch’s central differentiator. Switch’s decision to use a mix of microbes is also intended to reduce the location-to-location variability that he claims has dogged biological products.
Unlike approaches based primarily on selecting mutants that have spontaneously evolved to produce ammonia, meanwhile, Switch “has gone in and actually built this thing from the bottom up,” said Schnabel. “And that’s the reason that the regulatory approval for these field trials [from USDA and the EPA] is such a big deal because the level of complexity of the engineering is first in class.
“We have used parts from a virus. We’ve used used parts that don’t exist in nature. We have used parts from other bacteria. So it’s truly a bioengineering new in class type of biofertilizer microbe that we’re putting in the field.”
Regulatory and commercial outlook
Switch has secured permits for experimental field release and is targeting commercialization within two to three years.
The ambition is not to eliminate synthetic nitrogen entirely, said Schnabel, who noted that replacing 25% of nitrogen fertilizer while maintaining yields would constitute a major win, with biology’s likely upper limit around 50%.
The business case—which is coming into sharper focus as the Iran War roils energy and fertilizer markets—is based principally on supplying nitrogen at a lower cost with a relatively small dose of microbes applied in-furrow, said Schnabel.
“We have a techno-economic analysis that’s sitting behind this, but you can calculate exactly how many microbes you have to make per acre, and the cost of producing them is much less than the cost of producing 40 or 80 pounds of chemical nitrogen fertilizer.
“Farmers have paper thin margins, so even just $20 to $30 in savings per acre on fertilizer would be a huge deal.”
Switch is also in several late-stage partnership discussions with companies spanning agricultural retail, fertilizer and seeds, and expects to make announcements later this year.
“Reinventing fertilizer is one of the most consequential problems of our time, and Switch is one of the few companies with a real shot at solving it,” said Gareth Asten, general partner at Acre Venture Partners, an investor in Switch Bio. “Field trials are a major milestone on that path.”
Further reading:
🎥 Inside Faraday Earth’s bid to make cheap green ammonia without Haber-Bosch
Can microbes supply half a crop’s nitrogen? Pivot Bio thinks so
US Senate fertilizer hearing: Farmers ‘can’t take much more’ as prices surge
Fertilizer spike adds up to $35/acre for US corn as Iran crisis deepens
