Overproduction of the Flv3B flavodiiron, enhances the photobiological hydrogen production by the nitrogen-fixing cyanobacterium Nostoc PCC 7120

Background: The ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen (H₂) is a promising alternative for renewable, clean-energy production. However, the most recent, related studies point out that much improvement is needed for sustainable cyanobacterial-based H₂ production to become economically viable. In this study, we investigated the impact of induced O₂-consumption on H₂ photoproduction yields in the heterocyte-forming, N₂-fixing cyanobacterium Nostoc PCC7120.

Results: The flv3B gene, encoding a flavodiiron protein naturally expressed in Nostoc heterocytes, was overexpressed. Under aerobic and phototrophic growth conditions, the recombinant strain displayed a significantly higher H₂ production than the wild type. Nitrogenase activity assays indicated that flv3B overexpression did not enhance the nitrogen fixation rates. Interestingly, the transcription of the hox genes, encoding the NiFe Hox hydrogenase, was significantly elevated, as shown by the quantitative RT-PCR analyses.

Conclusion: We conclude that the overproduced Flv3B protein might have enhanced O₂-consumption, thus creating conditions inducing hox genes and facilitating H₂ production. The present study clearly demonstrates the potential to use metabolic engineered cyanobacteria for photosynthesis driven H₂ production.