In 1977, researcher Rudolf Thauer proposed a theoretical ceiling on the amount of hydrogen that bacteria could produce via fermentation, the sugar-converting process also responsible for yogurt, beer and cheese.

Propelled by a genetic engineering technique that presents bacteria with a simple choice -- adapt or die -- research from the University of Nebraska-Lincoln just punched through that 40-year-old ceiling like Iron Man through papier-mâché.

A version of the Thermotoga maritima bacterium engineered by Raghuveer Singh, Paul Blum and their colleagues produced 46 percent more hydrogen per cell than a naturally occurring form of the same species. The team's highest reported yield -- 5.7 units of hydrogen for every unit of glucose fed to the bacterium -- easily surpassed the theoretical limit of 4 units.

The feat represents a breakthrough in the global effort to scale up the sustainable production of clean-burning hydrogen for vehicles and heavy industry, Singh said. Most commercial hydrogen comes from refining non-renewable fossil fuels such as natural gas, oil and coal -- processes that generate sizable amounts of carbon dioxide.

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