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

Abstract

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, the most recent, related studies point out that much improvement is needed for sustainable cyanobacterial-based H 2 production to become economically viable. In this study, we investigated the impact of induced O 2-consumption on H 2 photoproduction yields in the heterocyte-forming, N 2-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 H 2 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 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.

Flv3A facilitates O2 photoreduction and affects H2 photoproduction independently of Flv1A in diazotrophic Anabaena filaments

“…6d ). A recent report suggested that overexpressing heterocyst‐specific Flv3B leads to more stable microoxic conditions inside the heterocysts, notably increasing the H 2 production yield, presumably via the bidirectional hydrogenase Hox (Roumezi et al ., 2020 ). In contrast to the unidirectional production of H 2 by nitrogenase, Hox catalyses the reversible reduction of protons to H 2 (Bothe et al ., 2010 ).…”

Photosynthetic hydrogen production: Novel protocols, promising engineering approaches and application of semi‐synthetic hydrogenases

“…A recent study demonstrated that the heterocyst‐specific Flv3B enzyme actively eliminates O 2 thus enabling microoxic interior inside of the heterocyst, which supports diazotrophic growth and nitrogenase enzyme activity under illumination (Ermakova et al, 2014). Accordingly, overexpression of the Flv3B protein resulted in high H 2 photoproduction, even though this phenotype was not linked to enhanced nitrogenase activity (Roumezi et al, 2020). The latter requires further investigations.…”