Tuning near-infrared photosynthesis

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Photosynthesis is the source of all the food we eat, and almost all of the energy we use. This process uses sunlight to remove carbon dioxide from the atmosphere and converts it into sugars that feed the planet. Sunlight is captured by chlorophyll pigments that are arranged and held in place by proteins; these pigment-protein arrangements are known as antenna complexes. Antennas collect the light energy and funnel it towards specialised 'reaction centres', where the energy is converted to a form that can be used by the cell.Plants and cyanobacteria (blue-green algae) use chlorophyll (Chl) pigments to capture visible light (400-700 nm) to perform 'oxygenic' photosynthesis, releasing the oxygen that supports respiration. Additionally, a diverse range of bacteria are also capable of using far-red and near-infrared light (>700 nm), which we cannot see but feel as heat, to perform 'anoxygenic' photosynthesis. This mode of photosynthesis relies on the bacteriochlorophyll (BChl) pigments, rather than Chls.The majority of anoxygenic photosynthesisers use BChl a to harvest light between 750-900 nm, while a few use BChl b and harvest very low energy wavelengths >1000 nm. Most of the light between 900-1000 nm is absorbed by water in the atmosphere, so it is rarely used by naturally-occurring phototrophs. This project will reveal how BChl b-containing organisms are able to extend absorption past this rarely-used region, and whether it is possible to access even lower energy wavelengths to power photosynthesis. We will do this by creating new versions of the BChl b antenna-reaction centre complex able to capture unique ranges in the near-infrared. We will also measure how close together the pigments in these complexes are, and how quickly/efficiently energy can collected and funnelled to the reaction centre to power the cell.Achieving these aims will reveal how to control and tune absorption in the near-infrared region of the spectrum, and to see if the low-energy limit for photosynthesis can be surpassed, with the long-term goal of efficiently capturing the entire usable range of the solar spectrum to tackle some of humanity's impending fuel and food supply challenges in a sustainable manner.