Biofuel can now be generated from industrial greenhouse gas emissions. This is great news not just for the atmosphere but also for global food security.

While bioethanol is currently the most common renewable liquid fuel alternative to oil, its production uses up vast quantities of cereal crops because the starch they contain are a source of energy-rich carbon bonds.

But a novel approach perfected at MIT starts instead with carbon dioxide, carbon monoxide and hydrogen (PNAS; doi/10.1073/pnas.1516867113). This blend of ‘syngas’ as it’s known, is emitted in large volume from steel mills and municipal waste. Study author Amit Kumar expects that industries and councils will happily invest in a process that reduces their carbon footprint and makes them self-sufficient in their power use. “Our system is even better than free!”

The trick to turning gas into liquid fuel involves a tag-team metabolic process of bacteria and yeast. First, bacteria sealed in a metal canister are fed with syngas that they ‘fix’ into a liquid form as vinegar, a simple one-carbon compound. The trick developed by the MIT Laboratory of Bioinformatics and Metabolic Engineering was to pipe the vinegar directly to a second canister where yeasts metabolise it into fatty lipids up to 55 carbons long.

The longer the carbon chains, the more energy is packed in. The lipids are one only conversion step away from the combustible biodiesel, which gives much more bang for the buck than bioethanol, at a measly two-carbons. But getting the metabolism of the microbes to go in the right direction requires a lot of subtle tweaking of the conditions you grow them in, says Amit Kumar.

“It’s a really smart bug,” says Kumar fondly of the bacterium M. thermoacetica, so-called because it thrives in at temperatures close to 60°C without needing an air supply “This makes it very suitable for industrial applications, and since it’s the only organism that will survive at that those temperatures you avoid any contamination that would spoil the bioprocess,” he says.

The yeast Y. lipolytica is even smarter. The research team, led by Gregory Stephanopoulos, genetically engineered it to generate even longer lipid chains than it does in nature. While the yeast expels carbon dioxide, this can be cunningly fed back into the first stage. “That’s the elegance of the system,” says Amit Kumar. “You really close the cycle so that it continues to fix carbon.”

The researchers are setting up field trials in a handful of Chinese steel-mills that will test the system on a larger scale.

PNAS, 2016 Mar 7