The interesting applications of hydrogen as a fuel and in the chemical industry are providing a driving force for developing more efficient, fully sustainable hydrogen-production methods. In recent years, production of “biohydrogen” from carbohydrate-rich substrates via microbial fermentation has received increased attention. Due to biochemical and thermodynamic limitations, a maximum of four moles of hydrogen can be obtained when one mole of glucose is exclusively oxidized to two moles of acetate. However, the majority of hydrogen-producing fermentations reported in literature, which are carried out using mixed cultures, are resulting in much lower hydrogen yields than the theoretical maximum.We have previously identified Caldicellulosiruptor spp. as potential candidates for biohydrogen production since they efficiently produce hydrogen from various carbohydrates at high yields. In the present work, we combined two Caldicellulosiruptor spp. in a defined co-culture for biohydrogen production. The population dynamics in a continuous hydrogen-production system under different conditions were followed using quantitative real-time PCR. Interestingly, the two species stably co-existed in the system under both carbon and non-carbon limited conditions. The hydrogen yields obtained by the co-culture at higher residence times were close to the theoretical maximum, as acetate was the main metabolic end product detected. These yields are at least twice as high as those obtained by most previously reported mixed cultures. Carbon limitation improved the sugar conversion efficiency and slightly increased hydrogen yield and productivity. Depending on the substrate, the developed co-culture might offer an attractive alternative to the traditional “undefined” mixed culture for a cost-effective biohydrogen process.
|Publication status||Published - 2009|