Overproduction of the cyanobacterial hydrogenase and selection of a mutant thriving on urea, as a possible step towards the future production of hydrogen coupled with water treatment.

Théo Veaudor,Franck Chauvat,Thichakorn Jittawuttipoka,Marcia Ortega-Ramos,Hervé Bottin,Corinne Cassier-Chauvat,Wolfgang R Hess

doi:10.1371/journal.pone.0198836

Abstract

Using a combination of various types of genetic manipulations (promoter replacement and gene cloning in replicating plasmid expression vector), we have overproduced the complex hydrogenase enzyme in the model cyanobacterium Synechocystis PCC6803. This new strain overproduces all twelve following proteins: HoxEFUYH (hydrogen production), HoxW (maturation of the HoxH subunit of hydrogenase) and HypABCDEF (assembly of the [NiFe] redox center of HoxHY hydrogenase). This strain when grown in the presence of a suitable quantities of nickel and iron used here exhibits a strong (25-fold) increase in hydrogenase activity, as compared to the WT strain growing in the standard medium. Hence, this strain can be very useful for future analyses of the cyanobacterial [NiFe] hydrogenase to determine its structure and, in turn, improve its tolerance to oxygen with the future goal of increasing hydrogen production. We also report the counterintuitive notion that lowering the activity of the Synechocystis urease can increase the photoproduction of biomass from urea-polluted waters, without decreasing hydrogenase activity. Such cyanobacterial factories with high hydrogenase activity and a healthy growth on urea constitute an important step towards the future development of an economical industrial processes coupling H2 production from solar energy and CO2, with wastewater treatment (urea depollution).

Highlights

In response to the constant increase in energy consumption and resulting pollution by the growing and developping world population, it is important to develop new energy sources that are plentiful, renewable and environmentally friendly
We found that the hydrogenase activity of both WT and CE1 cells could be increased by growing the cells in the mineral medium appropriately supplemented with extra iron (17 μM) and nickel (2.5 μM) metals required for the [NiFe] hydrogenase cluster
The gains conferred by the genetic engineering and growth-medium improvement could be cumulative as the hydrogenase activity of the CE1 mutant grow in the improved medium was about 10-fold higher than hydrogenase activity of WT cells grow in the standard medium cells [14] and this work (Fig 2)

Summary

Introduction

In response to the constant increase in energy consumption and resulting pollution by the growing and developping world population, it is important to develop new energy sources that are plentiful, renewable and environmentally friendly. Modification of hydrogenase and urease activities in Synechocystis PCC6803 study design, data collection and analysis, decision to publish, or preparation of the manuscript

Methods

Results

Discussion

Conclusion