Autotrophic and Mixotrophic Batch Processes with Clostridium autoethanogenum LAbrini in Stirred Tank Bioreactors with Continuous Gassing

Simultaneous conversion of syngas and sugars is a promising approach to overcome limitations of syngas fermentation. <i>Clostridium autoethanogenum</i> LAbrini, obtained by adaptive laboratory evolution, is known to show improved autotrophic process performance. Under purely autotrophic conditions, <i>C. autoethanogenum</i> LAbrini exhibits substantially faster growth and biomass formation compared to the wild-type in fully controlled, stirred-tank bioreactors with a continuous gas supply. In mixotrophic processes, the pre-culture strategy has a significant impact on the growth and metabolic activity of <i>C. autoethanogenum</i> LAbrini. <i>C. autoethanogenum</i> LAbrini can metabolize sugars (D-fructose, D-xylose, or L-arabinose) and CO simultaneously. All mixotrophic batch processes showed increased growth and product formation compared to the autotrophic process. The mixotrophic batch process with D-fructose enabled superior production of alcohols (10.7 g L^-1 ethanol and 3.2 g L^-1 D-2,3-butanediol) with a heterotrophic pre-culture. Using an autotrophic pre-culture and L-arabinose resulted in a total alcohol formation of more than 13 g L^-1. The formation of <i>meso</i>-2,3-butanediol (>0.50 g L^-1) occurred exclusively under mixotrophic conditions. Thus, <i>C. autoethanogenum</i> LAbrini, clearly representing notable improvements over the wild-type strain in mixotrophic batch processes, offers a good basis for further strain improvements to shift the product range even further towards more reduced products.