Batch and semi-continuous fermentation with Parageobacillus thermoglucosidasius DSM 6285 for H₂ production

Background: Parageobacillus thermoglucosidasius is a facultatively anaerobic thermophile that is able to produce hydrogen (H₂) gas from the oxidation of carbon monoxide through the water-gas shift reaction when grown under anaerobic conditions. The water-gas shift (WGS) reaction is driven by a carbon monoxide dehydrogenase-hydrogenase enzyme complex. Previous experiments exploring hydrogenogenesis with P. thermoglucosidasius have relied on batch fermentations comprising defined media compositions and gas atmospheres. This study evaluated the effects of a semi-continuous feeding strategy on hydrogenogenesis.

Results: A batch and two semi-continuous fermentations, with feeding of the latter fresh media (with glucose) in either 24 h or 48 h intervals were undertaken and H₂ production, carbon monoxide dehydrogenase (CODH) activity, and metabolite consumption/production were monitored throughout. Maximum H₂ production rates (HPR) of 0.14 and 0.3 mmol min^-1, were observed for the batch and the semi-continuous fermentations, respectively. Daily feeding attained stable H₂ production for 7 days, while feeding every 48 h resulted in high variations in H₂ production. CODH enzyme activity correlated with H₂ production, with a maximum of 1651 U mL^-1 on day 14 with the 48 h feeding strategy, while CODH activity remained relatively constant throughout the fermentation process with the 24 h feeding strategy.

Conclusions: The results emphasize the significance of a semi-continuous glucose-containing feed for attaining stable hydrogen production with P. thermoglucosidasius. The semi-continuous fermentations achieved a 46% higher HPR than the batch fermentation. The higher HPRs achieved with both semi-continuous fermentations imply that this approach could enhance the biohydrogen platform. However, optimizing the feeding interval is pivotal to ensuring stable hydrogen production.