Strong pH dependence of hydrogen production from glucose by Rhodobacter sphaeroides |
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| Affiliation: | 1. State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi''an Jiaotong University, Xi''an, 710049, China;2. Department of Environmental Science & Engineering, Xi''an Jiaotong University, Xi''an, 710049, China;3. College of Bioresources Chemical & Materials Engineering, Shaanxi University of Science & Technology, Xi''an, 710021, China;1. State Key Laboratory of Multiphase Flow in Power Engineering, Xi''an Jiaotong University, Xian 710049, Shaanxi, PR China;2. Department of Environmental Science & Engineering, Xi''an Jiaotong University, Xian 710049, Shaanxi, PR China;1. School of Agricultural Technology, Walailak University, Tasala, Nakhon Si Thammarat 80161, Thailand;2. School of Engineering and Resources, Walailak University, Tasala, Nakhon Si Thammarat 80161, Thailand;3. Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK;4. School of Engineering, Massey University, Private Bag 11 222, Palmerston North, New Zealand;5. Biomass and Oil Palm Center of Excellence, Walailak University, Tasala, Nakhon Si Thammarat 80161, Thailand;1. State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, China;2. Institute of Modern Facility Fisheries, Weifang University, Weifang 261061, Shandong, China;1. State Key Laboratory of Multiphase Flow in Power Engineering, Xi''an Jiaotong University, Xi''an, 710049, PR China;2. Department of Environmental Science and Engineering, Xi''an Jiaotong University, Xi''an, 710049, PR China |
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| Abstract: | Purple non-sulfur bacteria (PNSB) are well known for converting short-chain organic acids to H2, however, a decrease in pH caused by metabolic acids production limited H2 production during the photo-fermentation from glucose. Here we address why volatile fatty acids (VFA) excreted as fermentation products cannot be further degraded by R. sphaeroides that readily use them. We found that the photo-fermentation with pH controlled at 6.9 ± 0.1 resulted in a 90% increase of H2 yield and a 107.6% increase in volume H2 production relative to the pH-uncontrolled culture. Comparative fermentations on glucose at pH 5.8 and pH 7.1 using culture medium supplemented with 50% spent fermentation broth demonstrated that low pH alone is not the limiting factor and compounds present in the supernatants along with pH decrease were the most inhibitory to H2 production. The impact of byproducts VFA on phototrophic H2 production was dependent on both the pH and VFA concentrations; even 7 mM VFA addition totally inhibited H2 production from glucose at pH 5.4. H2 production with pH control for the Δhup strain was not discernibly different from the parent strain, which are all significantly higher than high-performance strains by metabolic engineering. These results demonstrate that pH dependent VFA inhibition can be turned into a driving force for enhanced H2 production from glucose by pH regulation. |
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| Keywords: | pH control Volatile fatty acids |
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