Evaluation of lab-defined syngas and acetate as substrates for H2 production with Parageobacillus thermoglucosidasius DSM 6285

Parageobacillus thermoglucosidasius is a carboxydotrophic microorganism that produces H₂ through the water-gas shift (WGS) reaction, using carbon monoxide (CO) as the main substrate. CO is a common constituent of syngas, alongside CO₂, H₂, O₂, and other gases. The facultatively anaerobic nature of P. thermoglucosidasius is particularly pertinent for hydrogenogenesis from O₂-containing syngas. Here, we evaluated the effects of different syngas compositions (5, 12, and 20% of H₂ gas, with constant CO and CO₂; 10, 30, and 50% CO gas with constant CO₂ and H₂) on hydrogenogenesis at the bioreactor scale. Electron balance analysis showed that 88-91% of electrons coming from CO were converted into H₂, regardless of the gas composition. The presence of H₂ in different compositions had no inhibitory effect on hydrogen production rate (HPR), and the maximum HPR corresponded to 13.65 L H₂ L⁻¹ day⁻¹ in fermentations containing 30% CO. A carbon source, other than CO, is needed for biomass formation of P. thermoglucosidasius. Acetate was shown to be the primary intermediate metabolite of glucose metabolism, but could also be used as an initial carbon source for biomass generation. When this carbon source was used, most electrons from CO were converted to H₂, demonstrating that this organic acid can be used as an effective alternative to glucose for H₂ production with P. thermoglucosidasius. KEY POINTS: • Evaluation of lab-defined syngas at different compositions for H2 production with P. thermoglucosidasius at the bioreactor scale. • Hydrogen presence in the headspace was not inhibiting for subsequent H2 production. • Acetate can replace glucose to generate biomass when growing P. thermoglucosidasius.