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In the prospect of engineering cyanobacteria for the biological photoproduction of hydrogen, we have studied the hydrogen production machine in the model unicellular strain Synechocystis PCC6803 through gene deletion, and overexpression (constitutive or controlled by the growth temperature). We demonstrate that the hydrogenase-encoding hoxEFUYH operon is dispensable to standard photoautotrophic growth in absence of stress, and it operates in cell defense against oxidative (H₂O₂) and sugar (glucose and glycerol) stresses. Furthermore, we showed that the simultaneous over-production of the proteins HoxEFUYH and HypABCDE (assembly of hydrogenase), combined to an increase in nickel availability, led to an approximately 20-fold increase in the level of active hydrogenase. These novel results and mutants have major implications for those interested in hydrogenase, hydrogen production and redox metabolism, and their connections with environmental conditions.

Sco (for the synthesis of cytochrome c oxidase) is a mitochondrial membrane protein essential for the correct assembly of cytochrome c oxidase. sco homolog genes exist in a wide variety of bacterial species. Inactivation of Agrobacterium tumefaciens sco leads to markedly decreased cytochrome c oxidase activity. This phenotype can be complemented by either supplementing the culture medium with copper or by a plasmid containing sco. The sco mutant also alters resistance to a superoxide generator menadione and H2O2. Mutational analysis of conserved cysteine residues and a histidine residue within the putative copper ions binding motif of Sco indicates that these residues are essential for the biological activity of Sco. To summarize, we find that A. tumefaciens sco is required for the delivery of copper into active cytochrome c oxidase and in maintaining optimal resistance levels to oxidative stress.

In the prospect of engineering cyanobacteria for the biological photoproduction of hydrogen, we have studied the hydrogen production machine in the model unicellular strain Synechocystis PCC6803 through gene deletion, and overexpression (constitutive or controlled by the growth temperature). We demonstrate that the hydrogenase-encoding hoxEFUYH operon is dispensable to standard photoautotrophic growth in absence of stress, and it operates in cell defense against oxidative (H2O2) and sugar (glucose and glycerol) stresses. Furthermore, we showed that the simultaneous over-production of the proteins HoxEFUYH and HypABCDE (assembly of hydrogenase), combined to an increase in nickel availability, led to an approximately 20-fold increase in the level of active hydrogenase. These novel results and mutants have major implications for those interested in hydrogenase, hydrogen production and redox metabolism, and their connections with environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: We show that the Synechocystis AbrB2 repressor of hydrogen production, down regulates the defence against oxidative stress. The single widely conserved cysteine of AbrB2 is also shown to play a crucial role in AbrB2 oligomerisation, and in AbrB2-mediated repression of the hydrogenase encoding operon (hoxEFUYH) and a wealth of other genes. Very interestingly, our results indicate that this cysteine is the target of glutathionylation, which affects the binding of AbrB2 on the hox operon-promoter DNA, as well as the stability of AbrB2 at the non-standard temperature of 39 °C. Similarly, we show that the cysteine of the other hoxEFUYH regulator AbrB1 can also be glutathionylated in vitro. These novel findings will certainly stimulate the in depth analysis of the influence of glutathionylation on the production of hydrogen, a field totally overlooked so far. They also emphasize on the evolutionary conservation of glutathionylation, a process mostly described in eukaryotes, so far. [Copyright &y& Elsevier]