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Iron limitation as a growth-restricted cultivation strategy in the diazotrophic cyanobacterium Nostoc PCC 7120 ΔhupW for a new perspective on H2 production systems
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Karlsruhe Institute of Technology (KIT), Institute of Process Engineering in Life Sciences III Bioprocess Engineering, Karlsruhe, Germany.
Karlsruhe Institute of Technology (KIT), Institute of Process Engineering in Life Sciences III Bioprocess Engineering, Karlsruhe, Germany.
Karlsruhe Institute of Technology (KIT), Institute of Process Engineering in Life Sciences III Bioprocess Engineering, Karlsruhe, Germany.
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(English)Manuscript (preprint) (Other academic)
Keywords [en]
Cyanobacteria, H2 production, Growth limitation, biofuels, iron, magnesium, nutrient depletion, heterocyst, cultivation strategies, iron deprivation
National Category
Natural Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-390473OAI: oai:DiVA.org:uu-390473DiVA, id: diva2:1341758
Available from: 2019-08-11 Created: 2019-08-11 Last updated: 2019-08-14
In thesis
1. Heterocystous cyanobacteria, Dps proteins and H2 production
Open this publication in new window or tab >>Heterocystous cyanobacteria, Dps proteins and H2 production
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To mitigate climate change, CO2-emitting technologies have to be exchanged by renewable alternatives such as H2. H2 can be produced by cyanobacteria, but major efforts to enhance H2 production yields by genetic modifications or optimised cultivation conditions resulted in energetic photo-to-H2 conversion efficiencies of 4.0 %, far from its theoretical maximum. New concepts to enhance photobiological H2 production are described in two separate thesis chapters.

In photobioreactors, photosynthesis can lead to high O2 concentrations promoting oxidative stress that decreases the photosynthetic efficiency. Genetic modifications could potentially increase the cellular robustness facing oxidative stress e.g. by the introduction of Dps proteins. This protein class is known to mitigate oxidative stress, but cyanobacterial Dps proteins are fairly unexplored. In the 1st thesis chapter, I searched to identify the function of five Dps proteins from the filamentous and heterocystous cyanobacterium Nostoc punctiforme. Since the physiologically active Dps proteins are twelve subunit complexes, various methods were utilised to verify their multimeric state and stability. All five NpDps formed high multimeric complexes that allowed for further enzymatic characterisations. In spectroscopic analyses NpDps1-3 were found to utilise H2O2 for Fe2+ oxidation, whereas NpDps4 only used O2. NpDps4 crystal structures revealed an uncommon ferroxidase center (FOC) with a His character. This His-type FOC was found across the cyanobacterial phylum. Based on their O2 and H2O2 consumption, all four NpDps display interesting candidates to enhance the cellular robustness in photobioreactors.

To enhance H2 production yields, a reallocation of photosynthetic energy from cell growth to H2 production is required. In the 2nd thesis chapter, Nostoc PCC 7120 ΔhupW was set under iron starvation to evaluate this cultivation strategy for the purpose of H2 production. The Fe-limited culture comprised a ~ 5.3 fold lower chlorophyll a and a ~ 4.5 fold higher specific carbohydrate concentration as compared to the control. The Fe-limited cells retained long filaments with high heterocyst frequency of ~ 6 %. The microoxic environment inside heterocysts enables efficient H2-production from O2-senstive photo fermentative pathways. Therefore, iron-starvation could display the basis of enhanced H2 production on the cost of growth. For this purpose a biofilm-containing photobioreactor was designed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 89
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1837
Keywords
H2 production, Cyanobacteria, Dps, ferritin-like proteins, iron, nutrient limitation, oxidative stress, biofilm, photobioreactor, iron homeostasis, H2O2
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-390471 (URN)978-91-513-0716-9 (ISBN)
Public defence
2019-10-02, Lecture hall 80101, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Supervisors
Available from: 2019-09-10 Created: 2019-08-13 Last updated: 2019-10-15

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