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Abstract Cyanobacteria contribute to roughly a quarter of global net carbon fixation. During diel light/dark growth, dark respiration substantially lowers the overall photosynthetic carbon yield in cyanobacteria and other phototrophs. How respiratory pathways participate in carbon resource allocation at night to optimize dark survival and support daytime photosynthesis remains unclear. Here, using the cyanobacterium Synechococcus elongatus PCC 7942, we show that phosphoketolase integrates into a respiratory network in the dark to best allocate carbon resources for amino acid biosynthesis and to prepare for photosynthesis reinitiation upon photoinduction. Moreover, we show that the respiratory Entner–Doudoroff pathway in S. elongatus is incomplete, with its key enzyme 2-keto-3-deoxy-6-phosphogluconate aldolase exhibiting alternative oxaloacetate decarboxylation activity that modulates daytime photosynthesis. This activity allows for the bypassing of the tricarboxylic acid cycle when ATP and NADPH consumption for biosynthesis is excessive and imbalanced relative to their production by the light reactions, thereby preventing relative NADPH accumulation and ensuring optimal photosynthetic carbon yield. Optimizing these metabolic processes offers opportunities to enhance photosynthetic carbon yield in cyanobacteria and other photosynthetic organisms under diel light/dark cycles.
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This content will become publicly available on April 9, 2026
Optimizing cyanobacterial hydrogen production: metabolic and genetic strategies with glycerol supplementation
IntroductionDeveloping sustainable hydrogen production is critical for advancing renewable energy and reducing reliance on fossil fuels. Cyanobacteria, which harness solar energy through photosynthesis, provide a promising biological platform for hydrogen generation. However, improving hydrogen yields requires strategic metabolic and genetic modifications to optimize energy flow and overcome photosynthetic limitations. MethodsFour cyanobacterial species were evaluated for their hydrogen production capacities under varying experimental conditions. Photosynthesis was partially inhibited using distinct chemical inhibitors, including 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Exogenous glycerol was introduced as a supplementary carbon source. Hydrogen production was monitored over time, and rates were normalized to chlorophyll a content. Genomic analysis of transporter proteins was conducted to identify potential genetic loci for further enhancement of hydrogen output. ResultsNitrogen-fixingDolichospermumsp. exhibited significantly higher hydrogen production compared to the other tested species. Supplementation with glycerol notably increased both the rate and duration of hydrogen evolution, far exceeding previously established benchmarks. The maximum hydrogen production rate forDolichospermumsp. reached 132.3 μmol H₂/mg Chl a/h—representing a 30-fold enhancement over the rates observed with DCMU. Genomic screening revealed key transporter proteins with putative roles in carbon uptake and hydrogen metabolism. DiscussionThese findings underscore the potential of cyanobacteria, particularlyDolichospermumsp., as robust platforms for sustainable hydrogen production. The substantial improvements in hydrogen yield highlight the importance of targeted metabolic engineering and carbon supplementation strategies. Future work focused on optimizing identified transporter proteins and refining genetic interventions could further enhance biohydrogen efficiency. By leveraging the inherent photosynthetic machinery of cyanobacteria, this platform offers a renewable hydrogen source with significant promise for global energy sustainability.
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- Award ID(s):
- 2233695
- PAR ID:
- 10590532
- Publisher / Repository:
- Frontiers in Energy Research
- Date Published:
- Journal Name:
- Frontiers in Energy Research
- Volume:
- 13
- ISSN:
- 2296-598X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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