A device invented at Ohio State University (OSU) is said to have dramatically boosted the production of a chemical that performs tasks as diverse as scenting perfume and flavouring Swiss cheese.
Engineers at OSU 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 by-products that normally result from propionic acid fermentation, cutting one by-product by more than half, said Shang-Tian Yang, professor of chemical engineering at Ohio State.
The bioreactor grows cells inside a bundle of fibres. Yang and his colleagues have previously shown that they could control the growth and differentiation of cells by changing the packing density of the fibres in the bioreactor.
Yang and doctoral student Supaporn Suwannakham reported yesterday that they were able to produce 72 grams of propionic acid per litre of sugar solution inside the bioreactor. Traditional fermentation typically yields only 50 grams per litre 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 immobilised the cells on the fibres 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 optimise the cells’ physical environment.”
The bioreactor can grow cells for a variety of applications including fermentation, animal cell culture, tissue engineering, and waste water treatment. Since 1998, Yang and his colleagues have used the device to make large quantities of a protein – Developmental Endothelial Locus-1 Protein – for cancer research. A commercial company recently licensed the technology for agricultural applications.
Yang designed the bioreactor as a three-dimensional alternative to the flat petri dishes and trays that scientists traditionally use to culture cells. The fibres anchor living cells in place as they grow and reproduce.
For this latest study, the engineers grew P. acidipropionici in a sugar solution, and gradually adjusted the sugar concentration so the cells would tolerate, and produce, higher concentrations of propionic acid. Tests yielded an average of 72 grams of the acid per litre. The bioreactor also produced 52 percent less succinate and 14 percent less acetate, two chemicals that industry normally has to remove from the fermentation mix before the propionic acid can be used.
When Yang and Suwannakham examined the cells from the bioreactor, they found that the cells had mutated and changed several key enzyme activities. Production of enzymes for propionic acid formation had increased, and the enzyme for succinate production had decreased.
Aside from giving Swiss cheese its characteristic smell and flavour, propionic acid is often used as a preservative and flavour enhancer for a wide variety of cheeses and baked goods.
In the chemical industries, it’s used as an ingredient for dyes, perfumes, pharmaceuticals, herbicides, rubber, and plastic.
With today’s growing emphasis on organic or “all-natural” products, Yang sees a market for propionic acid made without chemical additives in the bioreactor. “A company could conceivably market a product as being made with ‘all-natural’ propionic acid,” he said.