Researchers at Chalmers University of Technology, Sweden, have identified two main challenges for renewable biofuel production from cheap sources: lowering the cost of developing microbial cell factories; and establishing more efficient methods for hydrolysis of biomass to sugars for fermentation.

In a paper published in the journal Nature Energy, the researchers investigated the production of various biofuels using a model of yeast metabolism. They discussed how to develop novel systems and synthetic biology tools that can enable faster and cheaper construction of microbial cell factories and thereby address the first challenge, as well as recent advances in biomass processing that will likely lead to overcoming the second challenge in the near future.

The study, by Professor Jens Nielsen, Yongjin Zhou and Eduard Kerkhoven, from the Division of Systems and Synthetic Biology, evaluates the barriers that need to be overcome to make biomass-derived hydrocarbons a real alternative to fossil fuels.

It is technically already possible to produce biofuels from renewable resources by using microbes such as yeast and bacteria as tiny cell factories. However, in order to compete with fossil-derived fuels, the process has to become much more efficient. But improving the efficiency of the microbial cell factories is an expensive and time-consuming process, so speeding-up the cell factory development is therefore one of the main barriers.

Professor Jens Nielsen and his research group are world leaders in the engineering of yeast, and in the development and application of computer models of yeast metabolism. Their work informs how yeast can best be engineered to manufacture new chemicals or biofuels.

We have calculated theoretical maximum production yields and compared this to what is currently achievable in the lab. There is still huge potential for improving the process.

—Eduard Kerkhoven

Development of a microbial cell factory for hydrocarbon production from raw materials. From a proof-of-concept stage, where preliminary pathway engineering results in low titers on a small scale, the titer, rate and yield are improved through multiple rounds of the design-build-test-learn (DBTL)-cycle. Each part of this cycle can be aided by various techniques, and innovations in these areas will speed-up and improve the efficiency of the DBTL-cycle. Further genetic engineering of the cell factory by removing competing pathways and optimizing co-factor recycling increases titers while cultures are performed on a larger scale. The final step towards industrial application is the scale-up and improvement of robustness of the cell factory that now has high titre, rate and yield on a very large scale. Zhou et al.

The other main barrier is efficient conversion of biomass to the sugars that are used by the cell factories. If this conversion were made more efficient, it would be possible to use waste material from the forest industry, or crops that are purposely grown for biofuels, to produce a fully renewable biofuel.

In the future, whilst passenger cars will be primarily electric, biofuels are going to be critical for heavier modes of transport such as jets and trucks. The International Energy Agency projects that by 2050, 27 percent of global transport fuels will be biofuels. Meanwhile, large oil companies such as Preem and Total also predict that renewable biofuels will play an important role in the future. In their Sky Scenario, Shell expects that biofuels will account for 10% of all global end energy-use by the end of the century. That is in line with our research too.

—Eduard Kerkhoven

Resources

• Yongjin J. Zhou, Eduard J. Kerkhoven & Jens Nielsen (2018) “Barriers and opportunities in bio-based production of hydrocarbons” Nature Energy doi: 10.1038/s41560-018-0197-x