Hydrogen Production in the Cyanobacterium Synechocystis sp. PCC 6803 with Engineered Subunit of the Bidirectional H2-ase

Abstract

Hydrogenase (H₂-ase) enzyme holds great promise as a bio-generator for bio-solar hydrogen (H₂) production. Consequently, an oxygen-tolerant H₂-ase is needed in a photosynthetic organism.  In this work, a mutant strain of Synechocystis sp. PCC 6803 with modified H₂-ase analyzed under various physiological conditions. The growth rate was higher than that of wt strain and cellular capacity to fix carbon was increased, as shown by higher glycogen accumulation. Oxygen evolution by mutant strain in chemostats was higher than by wt cells over a range of pH levels. The mutant displayed significantly higher hydrogen (H₂) production than wt cells, especially at high pH. Examinations of electron flow pathways in the presence of various inhibitors indicated that the genetically modified H₂-ase apparently behaves similarly to the wt with respect to its electron source. Remarkably, it was consistently observed H₂ production under continuous light conditions, in the presence of oxygen (O₂), under many circumstances in both chemostat and batch tests. H₂ production in the light was improved under alkaline pH in mutant strain than wt. The data suggest that the genetically modified hydrogenase (H₂ase) is a functionally active. Several lines of evidence suggest that O₂ may be important in draining electrons from the donor side of photosystem I (PSI) in turn increases the linear electron flow and thereby helping to feed the H₂ase activity. In conclusion, the bidirectional H₂ase in Synechocystis may play a critical role in cell physiology not only under anoxic conditions but also under O₂-evolving activity.

Keywords: Cyanobacteria, Hydrogen, Hydrogenase, Protein engineering.