Energy-producing bacterium engineered by Harvard scientist

Harvard Professor of Energy Daniel G. Nocera, the chemist who gave us the artificial leaf, has genetically engineered bacteria to absorb hydrogen and carbon dioxide and convert them into alcohol fuel.

When he announced that he was working with bacteria last year, he was aiming for 5% efficiency—about 5 times better than plants. This month at the University of Chicago, he announced his bug converts sunlight ten times more efficiently than plants.

“Right now we’re making isopropanol, isobutanol, isopentanol,” he said in a lecture to the Energy Policy Institute at Chicago. “These are all alcohols you can burn directly. And it’s coming from hydrogen from split water, and it’s breathing in CO2. That’s what this bug’s doing.”

Nocera’s artificial leaf, developed while he was at MIT, made a splash five years ago because the wafer of silicon and other elements can be dropped in water, exposed to sunlight, and it will continuously split the water into hydrogen and oxygen. Hydrogen, a clean burning fuel, is typically made from natural gas in a process that emits greenhouse gases.

But Nocera says that the world isn’t ready for hydrogen fuel just yet. “If I give you my renewable hydrogen the only thing you’ll do is blow up balloons with it,” he said. “There’s no infrastructure for hydrogen.”But if hydrogen from the leaf can combine with CO2 to make alcohol fuel, the fuel can be used the way diesel is now.

So over the last 18 months, Nocera worked with biologists from Harvard Medical School to engineer a bacteria called Ralston eutropha to consume hydrogen and CO2 and convert them into adenosine triphosphate (ATP), the energy molecule used by natural organisms. Building on discoveries made earlier by Anthony Sinskey, a professor of microbiology at MIT, they inserted more genes to convert the ATP into alcohol and cause the bacteria to excrete it.

“Light in, and these things just excrete it out, and then you can collect it,” Nocera said. His bacteria produce energy far more efficiently than plants do on their own. Plants convert sunlight to biomass at about 1 percent efficiency, he said, after using most of their energy to survive. Nocera’s bacteria produce biomass at 10.6 percent and alcohol at 6.4 percent efficiency. The alcohol can be burned directly. The biomass can be made into fuel.

“I can just let the bugs grow exponentially. They’re eating hydrogen, that’s their only food source, and then they breathe in CO2, and they keep multiplying. They procreate, and that goes into an exponential growth curve.”A one-liter reactor full of Nocera’s bacteria can capture 500 liters of atmospheric CO2 per day, he said. For every kilowatt hour of energy they produce, they’ll remove 237 liters of CO2 from the air.But much of that will return to the air when the alcohol is burned.

“This isn’t solving your CO2 problem,” he said. ”I’m taking CO2 out of the air, you burn it and you put the CO2 back. So it’s carbon neutral. I’m not going to reverse 400 ppm of CO2. But you’re not going to use any more stuff out of the ground.”

Because the leaf can make hydrogen from any water—dirty water, even urine—and CO2 is present to excess in the atmosphere, the technology has promise as a local renewable energy source in areas that lack an electric grid. So Nocera wants to develop it where distributed renewables could have the biggest impact—in India.

Where India lacks grid infrastructure, about 300 million of its people lack access to electricity. But that also means new energy sources can develop without having to compete with established industry.

He wants to find investors who will help him deliver the technology to Indian scientists, who can develop it domestically.

Source: Forbes