Shenzhen Advanced Institute has made new breakthroughs in the field of semi-artificial photosynthesis


Transmission electron microscope photo of the E. coli biofilm Source: Courtesy of the research team

“Everything grows by the sun”. Photosynthesis refers to the process by which plants or algae absorb sunlight, synthesize carbon dioxide and water into organic matter, and release oxygen.

The principle of semi-artificial photosynthesis, which has recently been very “hot” in the field of science, is also very similar, mainly through artificial methods to simulate photosynthesis, using light energy to catalyze the production of fuel molecules or various useful chemicals. Semi-artificial photosynthetic systems usually use semiconductors as light-absorbing materials, but in the reaction process, there are a series of problems such as light-absorbing materials that are incompatible with biological cells, resulting in poor photosynthesis effect and difficulty in recycling cells.

On May 7, Beijing time, a new study published in science progress, a sub-journal of Science, showed that bacterial biofilm can provide an ideal interface to physically separate semiconducting nanomaterials and bacteria at the micron scale, significantly reducing the damage of semiconductor materials to bacterial cell membranes under light conditions, and ultimately improving the stability and sustainability of semi-artificial photosynthetic systems. Using this designed interface, the researchers achieved efficient fixation of optically flooded carbon dioxide, providing an important tool for harvesting high value-added energy and chemicals.

This achievement was co-authored by Wang Xinyu, associate researcher of Zhong Chao’s research group at the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, and Zhong Chao, shenzhen Institute of Synthetic Biology Innovation, and Zhang Jicong, a doctoral student at ShanghaiTech University, as the co-first author of the article, and researcher Zhong Chao as the sole corresponding author.

Biofilm builds a “protective net” for cells

Current semi-artificial photosynthetic systems typically consist of two parts, absorbing and storing energy from sunlight, and engineered bacteria, which can use this energy to produce a variety of products useful to humans. Semiconductor materials are often used as semi-artificial photosynthetic absorbing materials because of their excellent light absorption properties.

However, while the semiconductor material absorbs the energy of sunlight, it will also generate a kind of “oxidation hole” around it, which is very toxic to bacteria, and in the reaction process, the photogenerated oxidation hole will cause damage to bacterial cells, and even cause the rupture of the entire cell, seriously affecting the normal operation of the “bacterial factory”.

So, how do you solve this problem?

In this study, the research team conducted a response design and study from the perspective of reducing the contact between semiconductor materials and bacteria. In the semi-artificial photosynthesis system, a solid compatible interface of biological materials + inorganic materials is constructed through the in situ mineralization mechanism of microorganisms of biological coatings through synthetic biology.

The researchers first redesigned the CsgA protein, the main component of the E. coli biofilm, at the genetic level, by fusing it with a short peptide with mineralization ability, allowing it to immobilize and load semiconductor particles in situ.

In this way, under the fixation of the biological coating, the semiconductor material is difficult to damage the bacteria, which is equivalent to artificially laying a protective net on the surface of the bacteria factory.

Just as humans work to eat, biological work also needs to absorb energy, semiconductors need to absorb light energy through the “safety net” to microbial cells, in order to make cells more motivated to “transform”.

“In the emerging field of semi-artificial photosynthesis, the team’s functional biofilm of E. coli through synthetic biology technology can play the role of a ‘safety net’.” Wang Xinyu said that by expressing extracellular insulation proteins with mineralization ability, direct contact between high-energy semiconductor materials and bacteria is avoided, which greatly reduces the damage to engineered bacteria.

Scientific means to help green manufacturing

Bacterial biofilm is ubiquitous in nature, composed of bacteria and their secreted extracellular matrix, this natural living material has the characteristics of programmable function, self-regeneration and environmental tolerance, so it has great application potential in large-scale photocatalysis. For example, in the current fermentation system, most of the suspended cells are used and cannot be fixed. Due to the inherent adherent growth characteristics of the biofilm, the continuous production of photocatalytic products can be realized through the design of the flow bed reactor.

Through engineering modification, the researchers have made the biofilm of E. coli have the ability to mineralize and fix carbon dioxide, and successfully construct a semi-artificial photosynthetic system that can achieve photocatalytic reduction of carbon dioxide to produce formic acid.

However, in the biofilm semi-artificial photosynthesis system, the researchers only introduced a single enzyme, and it was not possible to achieve the generation of high value-added economic products. In the future, the research team will continue to modify microorganisms, build a synthesis pathway from carbon dioxide to long-chain high-value-added chemical molecules, and conduct pilot fermentation attempts on the photocatalytic reaction system of biofilm to verify the large-scale production capacity of the resulting system.

At present, in the field of synthetic biology, there has been a major breakthrough in the conversion of carbon dioxide into starch or glucose in China, but the key first step of the whole system reaction, carbon dioxide fixation is still achieved by chemical catalytic methods, which increases the complexity of the reaction system. The study achieves whole-cell co2 fixation through the construction of semi-artificial photosynthetic system, and it is expected to realize the conversion of co2 based on whole-cell system to high value-added long-chain compounds through full-chain optimization in the future.

“We have used synthetic biotechnology engineering to modify the bacterial biofilm, constructed a new bio-inorganic compatible interface, and based on this, we have realized a semi-artificial photosynthesis system that can be recycled from single enzyme to whole cell scale, which provides a new idea for the development of sustainable semi-artificial photosynthetic systems in the future, and also reflects the broad application prospects of material synthetic biology technology in the field of energy.” Zhong Chao said. (Source: China Science Daily Diao Wenhui Zhao Zishan)

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