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Engineered Near-Infrared Photosynthesis

Periodic Reporting for period 2 - EngiNear-IR (Engineered Near-Infrared Photosynthesis)

Reporting period: 2017-12-01 to 2018-11-30

Photosynthesis is the source of all food and most energy resources on Earth, as well as the oxygen that we breathe. Plants perform photosynthesis, but they are only able to use a small fraction of the light that comes from the sun, bounded within the visible part of the spectrum, i.e. light that we are able to see. Light at wavelengths longer than 700 nm are invisible to both us and plants, but there are photosynthetic bacteria that exist that are able to capture and use wavelengths past 1000 nm. They are able to do this because of the specialised pigments that they use to capture the light, and the proteins that bind these pigments and hold them in place. By understanding how these organisms capture this energy, it may be possible to combine their pigment/protein systems with those used by plants to create organisms that are able to use a much broader range of the solar spectrum, thus making the process of photosynthesis more efficient.

Improvements in photosynthetic efficiency could lead to the improvement of crop yields and growth season lengths, an important approach to tackling the increasing food and fuel shortage that is occurring with an ever-expanding world population.

The objectives of EngiNear-IR are to complete the pigment biosynthesis pathways for chlorophylls and carotenoids found in nature, and to engineer modified proteins to house these pigments in photosynthetic cells, in order to develop complexes that are able to capture underutilised wavelengths of light between 700-1000 nm.

At the conclusion of the project the pathways for the biosynthesis of all of the photosynthetic pigments in green sulfur bacteria have been solved, and this work has provided avenues for the completion of the same pathways in purple bacteria. We also have a greater understanding of how photosynthesis evolved to extend into the near-infrared, guided by the arrangement and packing of chlorophylls in light-harvesting complexes, which will inform the engineering of new strains of bacteria that can be harnessed for biotechnological purposes, and the design of biohybrid and synthetic light-capturing devices for sustainable energy production. I was also involved in work that discovered the enzyme used to synthesise chlorophyll f, that some specialised cyanobacteria use to perform photosynthesis in far-red light; modification of plants to use this pigment could result in greater crop yields and season lengths, providing more food to an increasingly populated planet.
The EngiNear-IR project has made progress in the validation of pigment biosynthesis pathways and the re-design of light-harvesting complexes in photosynthetic bacteria in an attempt to alter their spectral characteristics. Linked to this, a mechanism allowing specialised cyanobacteria (single-celled photosynthetic organisms that became the chloroplasts of plants) to use far-red wavelengths of light enriched in soil and shade helping them to out-compete their neighbours, has been studied in fine detail.

EngiNear-IR has produced genetically engineered strains of purple bacteria and green sulfur bacteria with modified pigment compositions and light-harvesting antenna complexes that are being used to evolve new photosynthetic capabilities. I have completed the pathways for carotenoid production in GSBs, and have revealed the remnants of a lost carotenoid pathway in Blastochloris viridis, an oxygen tolerant strain of which I have sequenced. I have also developed systems for the production and purification of two distinct forms of an enzyme that was key to expanding photosynthesis into the near infra-red.

In summary, this project has led to a greater understanding of the principles nature has employed to harvest near-infrared light, including the choice and arrangement of light-absorbing pigment cofactors, and their positioning defined by their protein scaffolds. This information can now be used to tune the absorption properties of pigment-protein complexes to underutilised regions of the spectrum (between 750-850 nm and 900-1000 nm), and inform the design of man-made, bioinspired photovoltaics that can contribute to the effort to switch to carbon-neutral technologies for energy production.

The work from EngiNear-IR has been presented at 4 international conferences, 3 meetings in the US, 1 meeting in the UK, and has led to the publication of 7 peer-reviewed papers.
My work takes a multidisciplinary approach to achieve the goals of EngiNear-IR by combining the fileds of synthetic biology, bioinformatics, mechanistic enzymology, and biophysics to improve our understanding of pigment biosynthesis, photosystem assembly and light harvesting processes. I am using genomics, transcriptomics and proteomics to understand how photosynthetic organisms respond to rapid changes in their environment (such as fluctuations in light and oxygen). By the end of the project I will have developed new organisms capable of photosynthesis by using wavelengths not currently used by plants, and will use cryoelectron microscopy to reveal the structural details of these new complexes, the technique for which the Nobel Prize for Chemistry was recently awarded. This work has future applications for constructing light-powered cell factories to produce high-value products including biofuels and pharmaceuticals, with the intellectual property owned by the European Union.
Hybrid photosynthetic membrane