Solvents in paints (esters) are currently produced mainly from oil. Photo Shutterstock Many special organic substances such as esters are made from petroleum. Anna Bohnenkamp’s PhD research reveals a sustainable alternative in a bacterium.
Esters are organic substances used as a flavouring in foods and beverages and as solvents for industrial purposes. To date, they are frequently manufactured from petroleum. Scientists are seeking more sustainable bio-based alternatives. Anna Bohnenkamp (Bioprocess Engineering) modified the bacterium Escherichia coli to efficiently produce ethyl acetate, a short ester. She obtained her PhD on this research in November.
Gene from yeast
E. coli does not naturally produce ethyl acetate. There are several yeasts that are able to, but not in the absence of oxygen. An oxygen-free environment, however, increases the efficiency of the production of ethyl acetate. Bohnenkamp extracted the gene that codes the enzyme Eat 1 (ethanol acetyltransferase) from yeasts. This enzyme transforms ethanol and acetyl co-enzyme A into ethyl acetate.
Bohnenkamp subsequently transferred the gene to E. coli in an anaerobe environment. The only thing required was to feed the bacterium with glucose. After further fine-tuning the reaction, she succeeded in doubling the production of ethyl acetate in the bacterium compared to the original situation, up to a yield of 60 per cent of the theoretical maximum.
Scaling up
The global demand for ethyl acetated is currently 4.75 million tonnes. The ester is used mainly in the paints and coatings industry. This market is expected to grow. Bohnenkamp conducted her experiments in a lab in fermentations with a volume of half a litre. Although the yield of the ester from the E. coli bacterium is comparable to that from the yeasts, Bohnenkamps expects scaling up the E. coli growing system will be simpler. This is due to the fact that oxygen is not needed, which must otherwise be distributed evenly throughout the reactor. Moreover, the productivity per cell is higher in E. coli than in yeasts because the bacterium’s growth is directly related to the production of ethyl acetate
