Background: The ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen (H 2 ) is a promising alternative for renewable, clean-energy production. However, studies of the topic in the last decade have shown that much improvement is needed before sustainable cyanobacterial-based H 2 production becomes economically viable. In this study, we investigated the impact of inducing O 2 -consumption to enhance H 2 photoproduction yields in the heterocyst-forming, N 2 -fixing cyanobacterium Nostoc PCC7120.
Results: The flv3B gene, encoding a flavodiiron protein naturally expressed in the heterocyst of Nostoc, was overexpressed. Compared to the wild type, the recombinant strain obtained displayed a significantly higher H 2 production under aerobic growth and phototrophic conditions. Nitrogenase activity assays indicated that flv3B overexpression did not increase the nitrogen fixation rates. On the other hand, quantitative RT-PCR experiments showed that the transcription of the hox genes, encoding the NiFe Hox hydrogenase was greatly elevated in the flv3B overexpressing strain.
Conclusion: We conclude that the overproduced Flv3B protein might have enhanced O 2 -consumption, thus creating conditions inducing hox genes and facilitating H 2 production. The present study clearly demonstrates the potential to use metabolic engineered cyanobacteria for photosynthesis driven H 2 production.