[NiFe] Hydrogenase from Alteromonas macleodii with Unusual Stability in the Presence of Oxygen and High Temperature

Hydrogenases are enzymes involved in the bioproduction of hydrogen, a clean alternative energy source whose combustion generates water as the only end product. In this article we identified and characterized a [NiFe] hydrogenase from the marine bacterium Alteromonas macleodii deep ecotype with unusual stability toward oxygen and high temperature. The A. macleodii hydrogenase (HynSL) can catalyze both H-2 evolution and H-2 uptake reactions. HynSL was expressed in A. macleodii under aerobic conditions and reached the maximum activity when the cells entered the late exponential phase. The higher level of hydrogenase activity was accompanied by a greater abundance of the HynSL protein in the late-log or stationary phase. The addition of nickel to the growth medium significantly enhanced the hydrogenase activity. Ni treatment affected the level of the protein, but not the mRNA, indicating that the effect of Ni was exerted at the posttranscriptional level. Hydrogenase activity was distributed similar to 30% in the membrane fraction and similar to 70% in the cytoplasmic fraction. Thus, HynSL appears to be loosely membrane-bound. Partially purified A. macleodii hydrogenase demonstrated extraordinary stability. It retained 84% of its activity after exposure to 80 degrees C for 2 h. After exposure to air for 45 days at 4 degrees C, it retained nearly 100% of its activity when assayed under anaerobic conditions. Its catalytic activity in the presence of O-2 was evaluated by the hydrogen-deuterium (H-D) exchange assay. In 1% O-2, 20.4% of its H-D exchange activity was retained. The great stability of HynSL makes it a potential candidate for biotechnological applications.