Engineers here have used their patented fibrous-bed bioreactor to genetically alter a bacterium so that it produces 50 percent more of the chemical propionic acid than the organism produces normally. And it did so without the aid of chemical additives employed in industry.
The device also reduced the amount of two unwanted byproducts that normally result from propionic acid fermentation -- cutting one byproduct by more than half, said Shang-Tian Yang, professor of chemical engineering at Ohio State.
The bioreactor grows cells inside a bundle of fibers. Yang and his colleagues have previously shown that they could control the growth and differentiation of cells by changing the packing density of the fibers in the bioreactor.
Monday at the national meeting of the American Chemical Society in Anaheim, Yang and doctoral student Supaporn Suwannakham reported that they were able to produce 72 grams of propionic acid per liter of sugar solution inside the bioreactor. Traditional fermentation typically yields only 50 grams per liter or less, making the new process 44 percent more effective.
More important to Yang is the fact that he and his team were able to coax the bacterium P. acidipropionici to make more acid without adding chemicals to the mix. They simply immobilized the cells on the fibers so the cells could grow and evolve -- or mutate -- in a harsh environment.
"Most labs focus on mixing the right chemical or biological cocktail to grow cells," he said. "We are the only group that I know of that is working to optimize the cells' physical environment."