Abstract
Sustainable chemical production from C(1) gaseous substrates, such as syngas or CO(2)/H(2), can be achieved through gas fermentation. In gas fermentation, acetogenic bacteria are able to utilize oxidized inorganic carbon sources as the sole carbon source and electron acceptor, while reduced inorganic species are used as the electron donor. Clostridium ljungdahlii, a model acetogen, is only capable of reducing CO(2) to acetate and ethanol, with H(2) as electron donor. In order to expand the product profile of this bacterium, five alcohol acetyltransferases (AATs) from yeast were heterologously expressed in C. ljungdahlii to evaluate its potential to produce ethyl acetate. When growing on CO(2) and H(2), up to 7.38 ± 0.43 mg/L of ethyl acetate were produced. Using fructose as the main carbon and energy source, up to 23.15 ± 1.28 mg/L of ethyl acetate were produced. Ethanol and fumarate supplementation were able to boost ethyl acetate titers (up to 37.51 ± 9.44 mg/L). Hence, ethyl acetate production was enabled in C. ljungdahlii at low titers, which could be explained by the high energetic cost of operation of AATs, and their shown promiscuity. However, we also show that this opens the door to more complex esterification reactions of higher added value biomolecules.