|Nghiem, Nhuan - John|
Submitted to: Biotechnology for Biofuels
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/22/2011
Publication Date: 9/2/2011
Citation: Khatibi, P.A., Montanti, J.M., Nghiem, N.P., Hicks, K.B., Berger, G., Brooks, W.S., Griffey, C.A., Schmale, D.G. 2011. Conversion of deoxynivalenol to 3-acetyldeoxynivlenol in barley derived fuel ethanol co-products with yeast expressing trichothecene 3-0-acetyltransferases. Biotechnology for Biofuels. 4:26. DOI: 10.1186/1754-6834-4-26. Interpretive Summary: Over 13 billion gallons of fuel ethanol were produced in the US in 2010 and almost all this product was made from corn kernels. During the production of that fuel ethanol, over 40 million tons of high protein dried distillers grains with solubles (DDGS) was also coproduced. US laws restrict the amount of corn that can be used to make fuel ethanol. ARS and other groups are exploring crops like winter barley as a biomass to produce needed advanced biofuels. Barley can become contaminated with toxic deoxynivalenol DON in the field following infection with the fungal plant pathogen Fusarium graminearum (Gibberella zeae) that causes a disease known as Fusarium head blight (FHB). Cost-effective and commercially viable methods to reduce mycotoxin contamination in DDGS need to be developed and implemented. Enzymes known as trichothecene 3-O-acetyltransferases have the ability to reduce the toxicity of DON by converting it to a less toxic product called 3ADON. In this study, we used gene common brewer’s yeast to ferment DON-infected modified barley into ethanol and DDGS. Analysis of these experiments showed that the transformed yeast did simultaneously convert the barley to ethanol and convert DON into less toxic 3ADON. To our knowledge, this is the first detailed report of yeast expressing a DON detoxification enzyme to reduce DON contamination during barley ethanol fermentation. While this work was done on the laboratory scale, the studies indicated that scale up of this process to commercial scale is technically feasible. If implemented, it could allow the safe use of DON contaminated grains for fuel and feed, rather than being disposed by landfilling or burning, which represents a major loss to the producer.
Technical Abstract: The trichothecene mycotoxin deoxynivalenol (DON) may be concentrated in dried distillers grains with solubles (DDGS), a co-product of fuel ethanol fermentation, when grain containing DON is used to produce fuel ethanol. Even low levels of DON (less than 5ppm) in DDGS sold as feed pose a significant threat to the health of monogastric animals. New and improved strategies to reduce DON in DDGS need to be developed and implemented to address this problem. Enzymes known as trichothecene 3-O24 acetyltransferases convert DON to 3-acetyldeoxynivalenol (3ADON) and reduce its toxicity in plants and animals. Two Fusarium trichothecene 3-O-acetyltransferases (FgTRI101 and FfTRI201) were cloned and expressed in yeast (Saccharomyces cerevisiae) during a series of small scale barley (Hordeum vulgare) ethanol fermentations. DON was concentrated 1.6 to 8.2 times in DDGS compared to the starting ground grain. During the fermentation process, FgTRI101 converted 9.2% to 55.3% of DON to 3ADON, resulting in DDGS with reductions in DON and increases in 3ADON when Virginia winter barley cultivars Eve, Thoroughbred, and Price and experimental line VA06H-25 were used. Barley mashes from the barley line VA04B-125 showed that yeast expressing FfTRI201 were more effective at acetylating DON than FgTRI101; DON conversion for FfTRI201 ranged from 26.1% to 28.3%, while FgTRI101 ranged from 18.3% to 21.8% in VA04B-125 mashes. Ethanol yields were highest with the industrial yeast strain Ethanol Red ®, which also consumed galactose when present in the mash. This proof of concept study demonstrates the potential of using yeast expressing a trichothecene 3-O-acetyltransferase to reduce DON during commercial fuel ethanol fermentation.