PEORIA, Ill. – Genetic modification of baker’s yeast could provide the answer to preventing a top cause of costly ethanol plant shutdowns – bacterial contaminations. These contaminations occur within ethanol fermentation systems when bacteria feed on glucose sugars in corn mash. This bacterial “bullying” can diminish yeast’s conversion of glucose into ethanol by up to 42 percent.

According to Dr. Shao-Yeh Lu, a research microbiologist at USDA’s National Center for Agricultural Utilization and Research (NCAUR) in Peoria, bacterial bullying can necessitate a shutdown of a biorefinery plant for cleaning and the use of antibiotics to eliminate the source. Failure to destroy the bacteria can inhibit the fermentation process from reaching its full production potential due to reduced efficiency. For a facility with 100 million gallon per-year capacity, such inefficiency could result in lost revenue of up to $4.5 million annually.

“In the corn ethanol process, corn is mashed and added to a tank, and then we add the yeast – brewer’s yeast or baker’s yeast, they are the same – and the yeast will ferment the corn mash utilizing the sugar that is in the corn to change it to ethanol. But the process itself is not sterile,” Lu told Farm World during a recent, exclusive visit to the historic “Peoria Ag Lab,” one of four USDA Agricultural Research Service (ARS) buildings constructed in the 1930s and the site where penicillin was refined for mass production during World War II. 

“There can be a lot of bacteria in there, and what these contaminants do is compete for the sugar, which is what the yeast is using to convert the mash to ethanol. The bullying occurs when the bacteria literally steals the sugar from the yeast,” said Lu, adding that high levels of contaminants can cause stress to the yeast which can halt the fermentation process. “A facility then has to shut down and get rid of the contaminant before they can start everything back up again. This process is inefficient and very expensive for these ethanol facilities.”

This is because ethanol plants historically rely on pricey antibiotics to kill bacterial contaminants fouling their fermenters. The more antibiotics used, the more likely the introduction of resistance to these bacteria, which can create a biofilm that is extremely hard to get rid of and serves as a reservoir for contaminants. “It will come to a point when these antibiotics are no longer good drugs, and the cycle goes on and on,” Lu explained.

By genetically modifying a baker’s yeast strain with a gene they discovered for making endolysin, Lu’s team created a specialized enzyme that kills the bacteria on contact. Large-scale trials have shown that use of the modified yeast strain in ethanol production reduced bacterial presence by up to 85 percent compared with a control group. Mash acetic and lactic acid levels were reduced by 40 and 71 percent, respectively, leading to an increase in ethanol production of as much as 40 percent.

According to Lu, this method is likely to prove more cost-effective than simply dumping bulk amounts of the enzyme directly into contaminated corn mash. The microbiologist is hopeful that larger-scale trials – the next phase of his project – will prove the genetically modified enzyme to be a better value for ethanol facilities while also increasing overall national ethanol output. 

“It will be a work in progress to get this technology to market and to get the (ethanol) industry to adapt it. Ultimately, we will have to do cost analysis and life cycle analysis, just to evaluate the feasibility of scaling this to industry (level). It has to be cheap enough for the industry to want to use this technology,” Lu said.

There are even larger implications to Lu’s work than simply increasing sustainability and profits of U.S. ethanol biorefinery facilities, which hold a combined production capacity of around 17 billion gallons annually. Increased efficiency at these plants, which are struggling to meet production quotas, could help the biofuels industry to make its case for expansion of the federal Renewable Fuels Standard and lessen the nation’s dependence on foreign oil while benefiting the environment.

“We’ve been working on this technology to help the industry for close to five years,” Lu said, while declining to speculate when his product might come to market. “More work needs to be done, and finding an industry partner that is willing to give us a try would definitely push that date up sooner. We are now looking for interest from the industry to try out our technology.”