ring darkness, Seibert said,the amount of hydrogen produced is minimal. But the team was able to solve the problem, said Seibert, by imposing a nutrient stress to the algae. First we grow out the algae, `fatten' it under normal photosynthetic conditions, he said. Then we withhold sulfur. Sulfur is critical for the completion of normal photosynthesis, Seibert said. In the absence of the element, the algae ceased emitting oxygen and stopped storing energy as carbohydrates, protein and fats. Instead, the algal cells began using an alternative metabolic pathway to exploit stored energy reserves anaerobically - in the absence of oxygen. The hydrogenase was activated, splitting large amounts of hydrogen gas from water and releasing it as a byproduct.
The significant thing is that the plant is using the energy of the sunlight to produce hydrogen, not oxygen, said Melis. Without sulfur, it produces a great deal more hydrogen in the presence of light than it does under normal circumstances in the dark. The algae ultimately would die if the nutrient stress were maintained for more than a few days, but they can be fattened again with sulfur and sunlight, allowing for repetitions of the process and continued harvesting of hydrogen gas. Eventually, the process could be used for the production of huge quantities of hydrogen. Hydrogen burns clean and hot, and it constitutes one-third of the water found in the Earth's oceans, rivers, lakes and atmosphere.
Cars already have been developed that run on hydrogen-powered devices known as fuel cells. These vehicles are virtually pollution-free; the only substance emitted from the tailpipe is water vapor. They do not release carbon dioxide or other heat-trapping gases, which are widely considered the primary culprits in global warming. Fuel cells big enough to power electrical generating plants could also be built. Our long-term goal is to develop strains of algae that we would grow in mass cultures to produce enormous quantities of hydrogen gas, said Melis. But at this point, we have to improve the production performance.