Abstract
BACKGROUND: The facultatively anaerobic thermophile Parageobacillus thermoglucosidasius is able to produce hydrogen gas (H(2)) through the water-gas shift (WGS) reaction. To date this process has been evaluated under controlled conditions, with gas feedstocks comprising carbon monoxide and variable proportions of air, nitrogen and hydrogen. Ultimately, an economically viable hydrogenogenic system would make use of industrial waste/synthesis gases that contain high levels of carbon monoxide, but which may also contain contaminants such as H(2), oxygen (O(2)) and other impurities, which may be toxic to P. thermoglucosidasius. RESULTS: We evaluated the effects of synthesis gas (syngas) mimetic feedstocks on WGS reaction-driven H(2) gas production by P. thermoglucosidasius DSM 6285 in small-scale fermentations. Improved H(2) gas production yields and faster onset towards hydrogen production were observed when anaerobic synthetic syngas feedstocks were used, at the expense of biomass accumulation. Furthermore, as the WGS reaction is an anoxygenic process, we evaluated the influence of O(2) perturbation on P. thermoglucosidasius hydrogenogenesis. O(2) supplementation improved biomass accumulation, but reduced hydrogen yields in accordance with the level of oxygen supplied. However, H(2) gas production was observed at low O(2) levels. Supplementation also induced rapid acetate consumption, likely to sustain growth. CONCLUSION: The utilisation of anaerobic syngas mimetic gas feedstocks to produce H(2) and the relative flexibility of the P. thermoglucosidasius WGS reaction system following O(2) perturbation further supports its applicability towards more robust and continuous hydrogenogenic operation.