Genomes to Life Contractor-Grantee Workshop III
February 6-9, 2005, Washington, D.C.
Genomics:GTL Program Projects
J. Craig Venter Institute
45
Development of a Novel Recombinant Cyanobacterial System for Hydrogen Production from Water
Qing Xu, Shibu Yooseph, Hamilton O. Smith, and J. Craig Venter (jcventer@tcag.org)
J. Craig Venter Institute, Rockville, MD
Hydrogen is a clean alternative to gasoline and other fossil fuels as it generates only water as a byproduct. The development of cost-effective and renewable approaches to produce hydrogen fuel will lead to a new and efficient energy system, which will address both the adverse environmental impacts of fossil fuels and the need for energy independence. Photobiological processes are attractive routes to renewable hydrogen production. With solar energy, photosynthetic microbes such as cyanobacteria can extract energy from water via oxygenic photosynthesis. The resulting energy can be coupled to a hydrogenase system that yields hydrogen. However, one major drawback of this process is that most hydrogen-evolving hydrogenases are irreversibly inhibited by oxygen, which is an inherent byproduct of oxygenic photosynthesis.
The overall goal of our project is to develop a novel, O2-tolerant photobiological system in cyanobacteria that can produce hydrogen continuously using water as the substrate. We have undertaken two general approaches to achieve this goal. Our first approach is to transfer known O2-tolerant NiFe-hydrogenase into cyanobacteria. It is reported that purple-sulfur photosynthetic bacterium Thiocapsa roseopersicina has an oxygen-tolerant evolving NiFe-hydrogenase, but this anoxygenic microbe can not split water. It is therefore logic to transfer the hydrogenase into cyanobacteria to construct a novel hybrid system that physically combines the most desirable properties of two bacteria. Thus far, we have cloned O2-tolerant hydrogenase genes hydS and hydL from T. roseopersicina into a cyanobacterial expression vector to create plasmid pEX-Tr, which was then transformed into Synechococcus sp. PCC7942. Analysis of pEX-Tr Synechococcus transformants are currently in the process. Our second approach is to identify putative O2-tolerant NiFe-hydrogenases from marine microbes and transfer them into cyanobacteria. Screening hydrogenase genes from the environment has been a useful approach to find novel O2-tolerant hydrogenases. However, to date, only a few O2-tolerant hydrogenases have been identified. To take advantage of the environmental genetic information generated by our ongoing Global Ocean Sampling Project, we currently use probabilistic modeling methods such as HMMs to search our sequence databases for putative NiFe-hydrogenases. We will transfer them into cyanobacteria for heterologous expression, and then screen for novel O2-tolerant hydrogenases using a chemochromic screening method developed by scientists at NREL. Thus far, we have identified a putative NiFe-hydrogenase that shows strong homology to a known O2-tolerant hydrogenase. Cloning the genes is in the process.
* Presenting author
