the invention provides oxygen - resistant iron - hydrogenases - hydrogenases ) for use in the production of h 2 . methods used in the design and engineering of the oxygen - resistant - hydrogenases are disclosed , as are the methods of transforming and culturing appropriate host cells with the oxygen - resistant - hydrogenases . finally , the invention provides methods for utilizing the transformed , oxygen insensitive , host cells in the bulk production of h 2 in a light catalyzed reaction having water as the reactant .