Ethanol and acetate production by Clostridium ljungdahlii and Clostridium autoethanogenum using resting cells

Abstract

Combined gasification and fermentation technologies can potentially produce biofuels from renewable biomass. Gasification generates synthesis gas consisting primarily of CO, CO(2), H(2), N(2), with smaller amounts of CH(4), NO(x), O(2), C(2) compounds, ash and tars. Several anaerobic bacteria species can ferment bottled mixtures of pure synthesis gas constituents. However, there are challenges to maintaining culture viability of synthesis gas exposed cells. This study was designed to enhance culture stability and improve ethanol-to-acetate ratios using resting (non-growing) cells in synthesis gas fermentation. Resting cell states were induced in autotrophic Clostridium ljungdahlii cultures with minimal ethanol and acetate production due to low metabolic activity compared to growing cell production levels of 5.2 and 40.1 mM of ethanol and acetate. Clostridium autoethanogenum cultures were not induced into true resting states but did show improvement in total ethanol production (from 5.1 mM in growing cultures to 9.4 in one nitrogen-limited medium) as well as increased shifts in ethanol-to-acetate production ratios.