The identification of DepB: An enzyme responsible for the final detoxification step in the deoxynivalenol epimerization pathway in devosia mutans 17-2-E-8
Carere, J., Hassan, Y.I., Lepp, D., Zhou, T. (2018). The identification of DepB: An enzyme responsible for the final detoxification step in the deoxynivalenol epimerization pathway in devosia mutans 17-2-E-8. Frontiers in Microbiology, [online] 9(JUL), http://dx.doi.org/10.3389/fmicb.2018.01573
Plain language summary
Wheat and corn are major crops produced in Canada but are prone to diseases caused by various fungi. One fungus in particular causes major agricultural diseases such as head blight in wheat and ear rot in corn often contaminates these grains with toxins. The main toxin, deoxynivalenol (vomitoxin), causes immense economic loss as its presence can reduce the value of the grain or, in severe cases, the grain must be discarded. Previously AAFC researchers demonstrated bacteria can modify this toxin, making it less toxic and also identified the first of two enzymes involved in this detoxification system. Here, we discovered the second enzyme responsible for this detoxification. We have investigated under what conditions this enzyme works and have shown that it functions well under a variety of conditions which may make it suitable to use as part of a detoxification procedure. Detoxifying grains contaminated with vomitoxin will help increase their value by making them suitable for consumption. This enzyme, along with the previously discovered enzyme, has the potential to be valuable to multiple stakeholders including farmers, millers and ethanol fermenters.
Deoxynivalenol (DON) is one of the most common mycotoxins found in cereal grains and grains contaminated with DON can cause health issues for both humans and animals and result in severe economic losses. Currently there is no feasible method to remediate affected grains. The development of a biological method for detoxification is becoming increasingly more plausible with the discovery of microbes which can transform DON to a relatively non-toxic stereoisomer, 3-epi-DON. Although bacteria capable of detoxifying DON have been known for some time, it is only recently an enzyme responsible was identified. In Devosia mutans 17-2-E-8 (Devosia sp. 17-2-E-8) a two-step DON epimerization (Dep) pathway, designated as the Dep system, completes this reaction. DepA was recently identified as the enzyme responsible for the conversion of DON to 3-keto-DON, and in this report, DepB, a NADPH dependent dehydrogenase, is identified as the second and final step in the pathway. DepB readily catalyzes the reduction of 3-keto-DON to 3-epi-DON. DepB is shown to be moderately thermostable as it did not lose significant activity after a heat treatment at 55°C and it is amenable to lyophilization. DepB functions at a range of pH-values (5-9) and functions equally well in multiple common buffers. DepB is clearly a NADPH dependent enzyme as it utilizes it much more efficiently than NADH. The discovery of the final step in the Dep pathway may provide a means to finally mitigate the losses from DON contamination in cereal grains through an enzymatic detoxification system. The further development of this system will need to focus on the activity of the Dep enzymes under conditions mimicking industrially relevant conditions to test their functionality for use in areas such as corn milling, fuel ethanol fermentation or directly in animal feed.