Approaches to developing biological H(2)-photoproducing organisms and processes.

The development of efficient biological systems for the direct photoproduction of H(2) gas from water faces several challenges, the more serious of which is the sensitivity of the H(2)-evolving enzymes (hydrogenases) to O(2), an obligatory by-product of photosynthesis. This high sensitivity is common to both FeFe and NiFe hydrogenases, and is caused by O(2) binding to their respective metallocatalytic sites. This overview describes approaches to (i) molecular engineering of algal FeFe-hydrogenase to prevent O(2) access to its catalytic site; (ii) transform a cyanobacterium with an O(2)-tolerant bacterial NiFe hydrogenase or (c) partially inactivate algal O(2)-evolution activity to create physiologically anaerobiosis and induce hydrogenase expression.