Acetic Acid Bioproduction by Acetobacterium woodii in Formate Medium in Continuous Bioreactors

Abstract

Acetogens hold significant potential for sustainable chemical production, thanks to their autotrophic metabolism and the associated synthesis of CO2 and H2. This thesis focuses on Acetobacterium woodii, a microorganism capable of utilizing the Wood-Ljungdahl pathway, enabling it to assimilate formate. Formate can be generated from CO2 using excess green energy and offers the advantage of easy transport in liquid or powder form. The primary goal of this research is to perform continuous fermentation in a chemically defined medium with formate as the sole carbon and energy source while investigating the limits of formate feed concentration and dilution rate. Initially, experiments were conducted in serum bottles, followed by the evaluation of production and uptake rates and acetate yield during continuous fermentation. The optimized strain achieved a dilution rate of 0.2 h-1, resulting in a substantial volumetric acetate production rate of 12.6 mmol L-1 h-1 and an optimum acetate yield of 0.223 mol mol-1 at a dilution rate of 0.1 h-1. This work successfully demonstrated that A. woodii can efficiently metabolize formate to acetate in a chemically defined medium. The relatively high dilution rate of 0.2 h-1 is likely attributed to the biofilm formed on the reactor wall. From a production standpoint, a controlled biofilm as a cell retention system is advantageous and desired. To evaluate maximum growth rates and specific rates, measures must be taken to prevent biofilm formation. In summary, A. woodii represents a promising pathway for efficient and sustainable biosynthesis of bulk chemicals.