| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 101 === Hydrogen is a clean alternative energy. The advantage of hydrogen is only produce energy and water after burning, and it has high energy content (122kJ/g). Hydrogen can be produced by physical, chemical or biological process. Purple non-sulfur bacteria (PNSB) is the major microbial group to produce hydrogen. The mechanism of PNSB to produce hydrogen is mainly mediated through nitrogenase, evolved to catalyze nitrogen fixation. Nitrogenase expression is regulated by NifA, which is a nitrogenase activator. However, NifA activity is affected by ammonium concentration. The high ammonium concentration can inhibit NifA activity, therefore it can’t regulate the gene, which related nitrogenase, to transcription, and nitrogenase can not be expressed. In this study, a R. palustris NifAnQ 24 mutant with an in-frame deletion of the Q region of chromosomal nifA gene was constructed from R. palustris WP3-5 to overcome the inhibition of nitrogenase activity by ammonium. A series of ammonium-rich mediums with acetate or lactate as carbon sources and ammonium chloride or glutamate as nitrogen sources were used to compare the hydrogen production between the wild-type strain WP3-5 and the mutant strain NifAnQ 24. The result showed that, hydrogen production of NifAnQ 24 was not significantly different from WP3-5 in glutamate-contained medium, indicated that nitrogenase expression were not affected in NifAnQ 24. On the other hand, WP3-5 could produce hydrogen only when the ammonium chloride in medium was below 0.9 mM, while NifAnQ 24 could produce hydrogen in the medium when ammonium chloride concentration was 7.5, 18.7, and 28.0 mM with acetate or lactate as carbon source. In the medium with lactate as carbon source and rich in
ammonium, the NifAnQ 24 SHPR was 97.36 mL-H2/g-biomass/day, and SCE is 27.8%. The result showed that NifAnQ 24 could successfully produce hydrogen by photo fermetation in ammonium rich medium. The possibility of increasing more carbon source distribution to hydrogen production than to growth by increasing initial cell concentration was also evaluated. The results indicated that, the hydrogen production of NifAnQ 24 couldn’t be improved by high initial cell concentration.
|
|---|
