Researchers discover a way to eliminate almost all DON toxicity in corn

A detox for contaminated corn may be just around the corner

As farmers think back to the challenges of the 2018 growing season, learning to deal with DON is probably top of mind. Indeed, it really was one of, if not THE worst year ever for managing the impacts of deoxynivalenol.

Not only did growers have trouble harvesting their infected corn, but delivery also became a nightmare. One or two elevators might reject a load only to have another finally accept it.

When dealing with research, it’s easy to become lost in differentiating between the possible and the plausible. In the past 10 years, growers have been enticed with tales of the tremendous promise of soybean-based lubricants, corn plants that can fix their own nitrogen and “wild” soybeans that break yield barriers. Research is good, of course, but sometimes growers just want immediate help for their problems in the field.

Now comes a revolutionary find by a research team with Agriculture and Agri-Food Canada (AAFC), of a bacterium that can reduce and detoxify DON in various scenarios. According to Dr. Ting Zhou, a researcher with the Guelph Research and Development Centre, the discovery came during a search for new strategies to deal with mycotoxins, which have been identified as a growing global threat in corn and wheat production. The bacterium was isolated from a soil sample gathered in an alfalfa field in southern Ontario and was found to reduce DON in different scenarios. In 2016, it was identified as Devosia mutans.

Dr. Ting Zhou and Dr. Xiu-Zhen Li are on the team that found bacterium to detoxify (DON).
photo: Courtesy Agriculture and Agri-Food Canada

“Although it is not clear how the bacterium interacts with the pathogen in the field, the naturally occurring bacterium modifies the DON molecular structure through a two-step transformation,” says Zhou. “That eliminates any toxicities associated with DON and renders the final wheat or corn products safe to consume or utilize in feed applications.”

It took years to understand the biology and the safety of the isolated bacterium, and also to track all of the final products associated with transforming the DON molecule. From there, the team needed to determine the toxicity of the final products in animal models and identify the enzymes involved, as well as the specifics of the catalytic process.

Zhou’s research team addressed those challenges through the use of state-of-the art genomic technologies, along with cell culture and animal models, resulting in the purification of the enzymes involved. At that point, they were able to identify two specific enzymes expressed by the Devosia mutans bacterium that detoxify DON. The first was designated as DepA, which oxidizes DON and changes its structure to 3-keto-DON, the intermediate step in the process. The second enzyme, identified as DepB reduces 3-keto-DON to 3-epi-DON, which is a “very stable” chemical compound (stereoisomer) of DON without its toxicities.

An image of the Devosia mutans bacterium under a transmission electron microscope.
photo: Courtesy Agriculture and Agri-Food Canada

“Both enzymes are effective in reducing DON toxicity but DepA reduces the toxicity by five-fold in comparison to the parental compound, DON,” says Zhou. On its own, that intermediate metabolite is not stable in the long term. “When that’s complemented with DepB activity, the final product is rendered less toxic by fifty-fold, where essentially no toxicity can be detected with the stable final product, 3-epi-DON.”

That is, there’s no toxicity detectable with currently available analytical and molecular methods.

Thus far, the enzymatic process has been 100 per cent effective in eliminating DON under laboratory conditions. This two-step approach can be modulated based on the final goals of each application. In theory, the DepA stage should provide enough detoxification of DON with respect to certain animal applications. Combining it with the second-stage (DepB) process would address any food- or feed-safety concerns. The only proviso is that the enzymatic process may require the use of certain co-factors, thereby adding to the cost. But the enzyme kinetics are stable at temperatures of up to 60 C with a near-neutral pH range (5 to 7), all of which are promising within an agricultural/industrial outlook.

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The bacterium was also tested using naturally contaminated corn where conditions of maximum DON transformations were seen. Zhou and his team recognize the importance of providing farmers with a ready-to-use and simple solution with consistent results, which is why they’re involved in projects that study large-scale usage.

The good news

Already, Zhou has been approached by several potential industrial collaborators, with the goal of moving this enzymatic process to its next stage where one of those participants can produce a product for food or feed applications. That raises the question of whether this will be delivered as a seed treatment or as a post-harvest application. Zhou believes there are advantages to either approach. A field treatment (seed coating or spray) would provide two distinct advantages, with the first being that it would protect plants from DON’s fungal pathogen.

“We know that DON is an influential factor in the disease development as it decreases plant immunity and initiates the necrosis that leads to full-scale infection at a later stage,” adds Zhou. “The second advantage is that most members of the Devosia bacterial genus are known for their ability to fix atmospheric nitrogen. This characteristic becomes an added benefit to the original goal of implementation as a bio-control agent.”

Another option in using this enzymatic process could be as a feed pre-treatment in fermentation silos or tanks. It also could be incorporated directly into livestock feed, where the detoxification would take place in the gut of the animals.

Beyond those delivery methods, there’s also the option for developing plants that over-express the enzymes, to further their benefits in protecting plants, animals and humans.

Onward and upward

At this point, the research efforts of Zhou and his team have created a solid foundation to further the application and delivery methods, and he believes they’re not far from seeing actual and empirical evidence to support the enzymes. Once identified, the industrial collaborators should take it to the commercialization phase.

“Based on the interest — in addition to the urgency around the globe to address the DON contamination dilemma, we believe that we are possibly two to three years away from the first commercial product,” says Zhou. “All of that depends on the appropriate industrial collaborations; among the biggest challenges is to find an industrial partner that has the capabilities for large-scale enzyme production.”

One question that often precedes the development and launch of a product, particularly one created in another country like the U.S., is “will it work under Canadian conditions?” Since the bacterium was isolated from a Canadian soil sample, it’s already adapted to agricultural practices that are in place here. Identifying the genes and working to develop a “Made-in-Canada” solution to DON is a huge discovery for AAFC researchers and the agri-food sector, in general.

“For almost three decades, the presence of DON biotransformation enzymes was hypothesized, but no team was able to provide conclusive evidence of such functionality,” says Zhou. “This will revolutionize the use of natural bacterial enzymes in combating DON. While the journey to completely eliminate DON from human food and animal feed is still in its infancy, the discovery of these enzymes provides the scientific community with a genuine template to work with.”

This article was originally published in the September 2019 issue of the Corn Guide.

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