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

## TL;DR

This paper shows how a modified strain of Clostridium autoethanogenum can efficiently convert syngas and sugars into alcohols in bioreactors.

## Contribution

The study demonstrates improved autotrophic and mixotrophic performance of a lab-evolved strain of Clostridium autoethanogenum.

## Key findings

- C. autoethanogenum LAbrini grows faster and forms more biomass under autotrophic conditions compared to the wild-type.
- Mixotrophic processes with sugars and CO increase alcohol production significantly compared to purely autotrophic processes.
- Using L-arabinose and an autotrophic pre-culture leads to the highest alcohol formation of over 13 g L−1.

## Abstract

Simultaneous conversion of syngas and sugars is a promising approach to overcome limitations of syngas fermentation. Clostridium autoethanogenum LAbrini, obtained by adaptive laboratory evolution, is known to show improved autotrophic process performance. Under purely autotrophic conditions, C. autoethanogenum 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 C. autoethanogenum LAbrini. C. autoethanogenum 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 meso-2,3-butanediol (>0.50 g L−1) occurred exclusively under mixotrophic conditions. Thus, C. autoethanogenum 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.