A new study led by Dr. Lin Su of Queen Mary University of London, published in the Journal of the American Chemical Society, describes a new integrated solar reactor in which engineered Escherichia coli (E. coli) are grown directly inside the same liquid that converts CO₂ into a usable energy source using sunlight.
In the future, this technology may be used to make environmentally clean chemicals, plastics, or even microbial protein.
The device combines an organic solar cell, a semiconductor electrode, two enzymes, and an engineered bacterium, and converts CO₂ and water into living biomass, reproducing the stages of natural photosynthesis without any plant, alga, or photosynthetic microbes.
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Su.
Tech Briefs: What was the biggest technical challenge you faced while developing this integrated solar reactor?
Su: The greatest hurdle was realizing autonomous, solar-driven CO2-to-biomass conversion in a single reactor, which required us to bridge the fundamental differences between abiotic and biotic environments. Specifically, we had to overcome three physicochemical compatibility barriers:
- Shared Microenvironment: We had to find a single liquid buffer that supported water oxidation at the photoanode, enzyme catalysis at the photocathode, and bacterial growth simultaneously. This was exceptionally tricky due to conflicting requirements; for instance, trace metals are essential for microbial growth but can inhibit electrocatalysis, and localized oxygen is needed for aerobic respiration but can deactivate the enzyme. Ultimately, we found that a simple sodium bicarbonate and potassium chloride buffer was tolerated by all three components.
- Chemical Toxicity: Traditional metallic CO2-reduction catalysts leach toxic ions like copper, silver, or tin into the culture, which kills the bacteria. We bypassed this by utilising a tungsten formate dehydrogenase (FDH) enzyme and a lead-free organic solar cell.
- Kinetic Matching: We had to carefully align the rate of electrochemical formate generation with the metabolic uptake rate of the microbes. If formate is produced faster than it is consumed, it accumulates, lowers the local pH, and ruins the enzyme's activity.
Tech Briefs: The article I read says, “This opens the way to swapping in engineered strains that produce target chemicals beyond biomass.” What could this mean for the future of the industry?
Su: For the industry, this represents a major step toward a "formate bioeconomy" that drastically reduces our reliance on traditional sugar feedstocks. We are not looking to replace plants, but rather to access chemistries that plants cannot perform, such as manufacturing industrial precursors, polymers, or speciality molecules without burning fossil fuels. Furthermore, because our system uses engineered bacteria that fix dissolved CO2 into biomass and use formate as an energy vector, it actively helps with carbon emissions. This approach could eventually open the way to supplying food and chemicals in a manner that uses far less land and water, helping to dampen the climate challenges we currently face.
Tech Briefs: Doc, you’re quoted in the article I read as saying, "While it is at an early stage, with the yields still small and the reactor running for hours rather than weeks, it is very promising.” My question is: Do you have any set plans for further research/work/etc.? If not, what are your next steps?
Su: Yes, we have several clear avenues for our next steps:
Enhancing Growth and Balancing Oxygen: Currently, our oxygen and nutrient management relies on operational workarounds rather than a clean chemical solution. We observed that hypoxic conditions severely inhibit bacterial growth and cause the bacteria to shift their metabolism toward producing acetate instead of biomass. We need to optimise this balance.
System Scalability: Because the current reactor runs for hours rather than weeks, improving long-term cyclic stability and scaling the system are top priorities.
Engineering for Valuable Compounds: While we focused on generating biomass in this study, we want to leverage our platform for targeted chemical synthesis. Interestingly, the "hypoxic switch" we discovered, where oxygen limitation channels fixed carbon into acetate, suggests a powerful strategy. By applying metabolic engineering, we could deliberately control this switch to channel fixed carbon into a diverse portfolio of valuable bioproducts.
Tech Briefs: Is there anything you’d like to add that I didn’t touch upon?
Su: I think the backstory of how this collaboration began is quite serendipitous. It started in May 2023 when Prof. Erwin Reisner visited the Weizmann Institute to give a lecture on his group's artificial leaves. Prof. Ron Milo showed Erwin his lab's engineered autotrophic E. coli, and they immediately realised the chemistry and biology could fit together perfectly. Ron even gave Erwin a signed copy of his book with an inscription, hoping they would join forces. Just two months later, Eliya Milshtein sent the first plate of the engineered bacteria to our lab in Cambridge. At the same time, Dr Celine Yeung was wrapping up her PhD project integrating organic photovoltaics with formate-producing enzymes. We had a robust, ready-to-go chemical platform, making it the perfect time to integrate it with the microbes.
Tech Briefs: Do you have any advice for researchers aiming to bring their ideas to fruition?
Su: My biggest piece of advice is to actively reach out to people and keep an open mind for suggestions. This project came together like a jigsaw puzzle shaped by years of disparate research, from materials chemistry to enzyme purification to synthetic biology. We could only achieve this through a cross-disciplinary approach, pairing isolated enzymes and semiconductors with engineered microbes. Don't be afraid to cross geographical boundaries and scientific disciplines to find the right collaborators.
