Hexanoate production from carbon dioxide with synthetic co-cultures

(M.Sc. Anna Stock)

In order to enable a sustainable economy, independence from fossil resources is required. One approach towards reducing emissions of climate-damaging gases is to utilize CO2 as a carbon source to produce organic substances. 

Autotrophically growing acetogenic bacteria are able to form acetic acid from CO2 and H2. Acetobacterium woodii is the most efficient acetogenic bacterium known to date and is capable of producing acetate from CO2 and H2 (gas fermentation). The production of longer chain organic acids with higher net value such as butyric acid or hexanoic acid can be carried out by other anaerobic bacteria, the so-called 'chain elongators', in mixed cultures. In this respect, one example is the anaerobic bacterium Clostridium drakei, which, however, can only convert lactic acid (and not acetic acid) to hexanoic acid. Therefore, Acetobacterium woodii was genetically modified by the cooperation partner at the University of Ulm (Frank Bengelsdorf, Chair of Microbiology and Biotechnology) so that it is now also capable to produce lactic acid from CO2 and H2. Previous research has already shown that hexanoate can be produced in a defined mixed culture of Acetobacterium woodii and Clostridium drakei (proof-of-concept).

The objective of this research project, undertaken in close cooperation with the University of Ulm, is to establish an optimal synthetic mixed culture of further genetically improved Acetobacterium woodii and Clostridium drakei in controlled, continuously gassed bioreactors to enable the efficient production of hexanoate from CO2 and H2 in one reactor with minimized by-product formation.