Acetate-containing supernatants from industrial off-gas cultivation enabling high-value product formation with established and emerging production organisms

Gas fermentation offers a sustainable alternative for valorizing climate-active gases and industrial off-gases. Currently, these gases require energy-intensive purification steps before they can be used in chemical processes such as Fischer-Tropsch synthesis. In gas fermentation, anaerobic bacteria produce acetate from industrial off-gases. Compared to chemical processes, the anaerobic bacteria offer greater tolerance to varying gas concentrations and impurities. One major product of these anaerobic valorization processes is acetate, which can be used as a co-substrate in a variety of biological processes. This study evaluates Corynebacterium glutamicum and Ustilago maydis in benchtop cultivations using 10-20% (v/v) sterile-filtered acetate-rich supernatants from Acetobacterium woodii fermentation to produce L-lysine and triglycerides. Partial substitution of glucose with these supernatants supported robust growth and required no additional purification beyond sterile filtration. C. glutamicum achieved a L-lysine concentration of 3.5 ± 0.27 g∙L^-1 and exhibited a diauxic growth pattern on glucose and acetate. In U. maydis, supernatant addition shortened the lag phase by approximately 2 h but reduced triglyceride yields modestly due to higher nitrogen availability. Optimizing the nitrogen-to-carbon ratio in benchtop fermentations resulted in a triglyceride concentration of 12.75 ± 1.17 g∙L^-1, demonstrating the feasibility of this approach. Collectively, the results demonstrate a viable method for replacing a portion of refined glucose with acetate-rich supernatants, thereby enabling a cost-efficient integration of anaerobic gas valorization with aerobic biomanufacturing.