Sunlight to Sugar without Plants

From Sunlight to SugarSunlight to Sugar without Plants

By Josh Nicks

Fancy some greenhouse gas in your tea? Researchers at the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany, have designed an artificial version of a chloroplast, the microstructures inside plant cells responsible for photosynthesis. Using sunlight and a chemical pathway designed by chemists instead of nature, to turn CO2 into sugar.1-2

Artificial photosynthesis could be used to build microscopic solar factories. This more efficient chemical pathway that the researches have designed beats anything found in nature, meaning it could actually help us remove CO2 from the atmosphere. However, at such an early stage in the project, whether or not this technology will get to that stage remains to be seen.

Fixing CO2, the process of turning it into sugar using enzymatic processes, is something that nature has multiple ways of doing. These chemists, lead by Prof. Tobias Erb have devised the seventh. They used a combination of thermodynamics and kinetics to redesign CO2 fixation and improve its efficiency. This new pathway is called the CETCH cycle, a network of enzymes 20% more energy efficient than the pathway used in natural forms of photosynthesis. To demonstrate that this might work in a living cell, a collaborator called Tarryn Miller isolated light-harvesting membranes from spinach, mixed them with the CETCH cycle enzymes, and showed they can work together. Why is this interesting? Well, it means that these scientists basically made a human-made chloroplast, in which the CETCH cycle enzymes use energy from the sun to turn CO2 into glycolate. Glycolate is a common chemical feedstock, used to make a range of organic products, including pharmaceuticals and biopolymers. So, not only could these artificial chloroplasts potentially help us remove CO2 from the atmosphere and fight climate change, but its possible they could be designed to produce usefil molecules that nature does not.

Labelled diagram of a chloroplast. Prof. Tobias Erb.

However, like a lot of cutting edge science, there are many obstacles to overcome before we see this technology succeed. The spinach membranes used to harvest solar energy degrade after a few hours, and isolating them to begin with is time consuming. Though according to Erb, a potential solution to this is to also produce artificial light harvesters.

In a recent Nature News articles, Yutestu Kuruma, a synthetic biologist at the Tokyo Institute of Technology, said ““we might be able to use the chloroplast mimics as an energy production system for artificial cells.” Though it would be ideal if these artificial chloroplasts could self-repair/reproduce, as natural chloroplasts are able to – something that hasn’t yet been achieved.3

These problems should not distract from this great work though. There’s a real possibility that we may one day have “synthetic plants” that not only use CO2 to breath, but also to feed themselves!

1. https://bit.ly/3bROJOb. 2. https://bit.ly/3fKCjbR. 3. https://go.nature. com/3yFyaif.

The massive enzymatic cycle developed by Erb and co-workers.