Enhancing CO2-Valorization Using Clostridium autoethanogenum for Sustainable Fuel and Chemicals Production

Abstract

20 Acetogenic bacteria can convert waste gases into fuels and chemicals. Design of 21 bioprocesses for waste carbon valorization requires quantification of steady-state carbon 22 flows. Here, steady-state quantification of autotrophic chemostats containing 23 Clostridium autoethanogenum grown on CO2 and H2 revealed that captured carbon (460 24 ± 80 mmol/gDCW/day) had a significant distribution to ethanol (54 ± 3 mol% with a 25 2.4 ± 0.3 g/L titer). We were impressed with this initial result, but also observed 26 limitations to biomass concentration and growth rate. Metabolic modelling predicted 27 culture performance and indicated significant metabolic adjustments when compared to 28 fermentation with CO as the carbon source. Moreover, modelling highlighted flux to 29 pyruvate, and subsequently reduced ferredoxin, as a target for improving CO2 and H2 30 fermentation. Supplementation with a small amount of CO enabled co-utilisation with 31 CO2, and enhanced CO2 fermentation performance significantly, while maintaining an 32 industrially relevant product profile. Additionally, the highest specific flux through the 33 Wood-Ljungdahl pathway was observed during co-utilization of CO2 and CO.