Assembly and evolution of a photosynthetic antenna

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 convert it into carbohydrates 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 assortment of bacteria are also capable of using light outside this range (>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, although Rhodospirillum rubrum is a well-studied example that unusually cannot harvest light effectively up to 850 nm because it lacks the common antenna complex. This project aims to transfer the antenna of another photosynthetic bacterium to Rhodospirillum rubrum, to allow the new, hybrid organism to capture light it was not previously able to. Further modifications to the new bacterium will be made by targeted alterations to the genome, and mutations will also be naturally acquired by growing the organism under light that can only be absorbed by the new antenna complex, a process that mirrors natural evolution, but that can be speeded-up in the laboratory. Achieving these aims will reveal how to assemble and regulate the production of pigment-protein complexes in other simple bacteria, with the long-term goal of putting boosted light-capturing ability to use to tackle some of humanity's impending fuel and food supply challenges in a sustainable manner. This could also have a positive effect on climate change; increased removal of CO2 greenhouse gas, and its conversion into sugars, could slow the warming of the planet, and mitigate the damage to the environment.