Researchers from Northwestern University, Evanston, Ill., and LanzaTech, Skokie, Ill., say they have developed a gas fermentation process that uses engineered bacteria to successfully convert carbon dioxide (CO2) into acetone and isopropanol (IPA), while avoiding the traditional use of fossil fuels.
“Manufacturing of these chemicals using conventional processes result in emissions of ~2 kg CO2/kg product along with accumulation of other toxic waste. Up to now, no sustainable, green chemistry alternative exists. We have developed a process that enables carbon-negative manufacturing of these chemicals, effectively pulling CO2 out of the atmosphere and locking ~1.5 kg of CO2 into the product per kg produced. So, as we move to larger scale, the process is carbon negative and this is significant,” explains Michael Jewett, co-senior author of the study and a professor at Northwestern’s McCormick School of Engineering.
The team started with Clostridium autoethanogenum, an anaerobic bacterium engineered at LanzaTech. Using synthetic biology tools, they next reprogrammed the bacterium to ferment CO2 to make acetone and IPA.
After performing lifecycle analysis, the team reported in the journal Nature Biotechnology that the carbon-negative platform could reduce CO2 by 160% compared to conventional processes.
Most commercial biomanufacturing processes are in the 1–5 g/L/h range, so, their current ~3g/L/h productivity for acetone and IPA already is commercially relevant, says Jewett.
The researchers note the approach is readily adaptable and could potentially help create streamlined processes for generating a wider range of commodity chemicals.
“We can adapt the organism by providing new enzymes that allow for the synthesis of new chemicals. We anticipate, as in this case, that we’ll also have to reprogram native metabolism to facilitate high yielding production,” Jewett elaborates.
The engineered strains also seem immune to poisoning by constituents commonly found in industrial emissions, syngas and other likely feed streams.
“This is one of the special features of this organism. It is tolerant to these contaminants. The process also is tolerant to fluctuations in the feedstock compositions, which is important for industrial-scale production and process stability,” notes Jewett.
Their next step is to demonstrate the process beyond pilot scale.
“Our vision for commercialization is to transform established ethanol-producing gas fermentation facilities into product-flexible production plants. By swapping the ethanol-producing microbe currently deployed in our commercial gas fermentation facilities, with a new microbe programmed for acetone or propanol production, or one of a number of other commodity chemical products, we can instantly increase the range of products that an individual facility can make. This product flexibility will enable plant operators to make market-based decisions on which products to focus on at any time,” explains Jewett.
LanzaTech’s two commercial plants have, to date, converted emissions from heavy industry into over 30M gallons of ethanol and avoided over 150,000 tons of CO2, says the firm.
For the initial industrial/commercial application of the engineered strains, the team believes it could tackle several possible waste streams.
“At a high level, we can use this process to convert industrial, agricultural and urban waste gases into important chemicals,” notes Jewett. For instance, LanzaTech already has developed technology to capture a steel mill’s waste gas (a mix of mostly CO, CO2, and hydrogen gas), which would otherwise be vented into the atmosphere.
“Acetone and IPA are important commodity chemicals with established markets of > $10 billion. Both molecules are industrial solvents as well as platform chemicals for the production of materials such as acrylic glass (polymethyl methacrylate) and polypropylene. A key feature of these molecules is that they can be separated using similar technology as ethanol, which allows us to use the same plant infrastructure at LanzaTech and switch between products (e.g., from ethanol to acetone or IPA) by simply changing the microbe. This is a paradigm shift to the chemical industry, where a plant is typically purpose-built for a certain product and production cannot be easily changed. We believe this approach is significant towards a circular economy,” declares Jewett.
“What’s so exciting is that we believe that the framework developed here will provide a blueprint for development of further carbon-negative chemical production processes. More broadly, our work highlights how synthetic biology has the potential to be a central pillar of a global strategy for enabling people and the planet to flourish in partnership,” Jewett concludes.
