Cyanobacterial H2 production - a comparative analysis

• Several unicellular and filamentous, nitrogen-fixing and non-nitrogen-fixing cyanobacterial strains have been investigated on the molecular and the physiological level in order to find the most efficient organisms for photobiological hydrogen production. These strains were screened for the presence or absence of hup and hox genes, and it was shown that they have different sets of genes involved in H2 evolution. The uptake hydrogenase was identified in all N2-fixing cyanobacteria, and some of these strains also contained the bidirectional hydrogenase, whereas the non-nitrogen fixing strains only possessed the bidirectional enzyme. In N2-fixing strains, hydrogen was mainly produced by the nitrogenase as a by-product during the reduction of atmospheric nitrogen to ammonia. Therefore, hydrogen production was investigated both under non-nitogen-fixing conditions and under nitrogen limitation. It was shown that the hydrogen uptake activity is linked tothe nitrogenase activity, wheras the hydrogen evolution activity of the bidirectional hydrogenase is not dependent or even reelated to diazotrophic growth consditions. With regard to large-scale hydrogen evolution by N2-fixing cyanobacteria, hydrogen uptake-decicient mutants have to be used because of their inability to re-oxidize the hydrogen produced by the nitrogenase. On the other hand, fermentative H2 production by directional hydrogenase should also be taken into account inn further investigations of biological hydrogen production.

Ämnesord

NATURVETENSKAP  -- Biologi -- Botanik (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Botany (hsv//eng)

Nyckelord

Cyanobacterium

hydrogen

hydrogenase

nitrogenase

photobiological H2 production

screening (H2 production)

Plant physiology

Växtfysiologi

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