Organisation, dynamics and biogenesis of a photosynthetic membrane

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Cyanobacteria are the oldest microorganisms that grow by photosynthesis in a similar way to plants. Cyanobacteria are widespread in our environment on Earth. For example, they are very abundant in rivers, lakes, and the oceans, and they make important contributions to the sustainable ecology of the planet. There are increasing interests in using cyanobacteria as possible sources of 'biofuels'. We may eventually be able to modify cyanobacteria to build new artificial cell "factories" that can use the energy of sunlight to produce fuels such as hydrogen. Cyanobacteria have a more complex cell structure than most bacteria. Inside the cells are the thylakoid membranes, a complex internal membrane system which is the site of the 'light reactions' of photosynthesis. The thylakoid membranes contain the pigments that absorb energy from sunlight and the proteins that carry out the first steps in converting solar energy to stored chemical energy. Although we now have a great deal of knowledge about the photosynthetic protein modules, we know rather little about how the thylakoid membranes are generated in nature. We propose to investigate this question using a 'model' cyanobacterium that can easily be genetically modified and have a regular shape of thylakoid membranes. We will first control the ability of cyanobacterial cells to produce thylakoid membranes. By switching the generation of thylakoid membranes in the cell and tagging the photosynthetic proteins with fluorescence, we will be able to watch in detail how proteins are synthesised and integrated into the thylakoid membrane during the membrane construction process using optical microscopy. To get more details on how the photosynthetic proteins are distributed in the thylakoid membrane, we will use a high-resolution microscope to scan the thylakoid membrane surface in order to determine individual proteins and their locations during the development of thylakoid membranes. The second section of this programme is to study how photosynthetic proteins interact with each other in the thylakoid membrane, which is important for their energy-transducing functions. For this purpose, we will label the proteins with different fluorescent tags and watch how different proteins move and assemble with others in the cell. We will also purify the protein complexes from cells and examine the protein composition of these complexes using biochemical techniques. Furthermore, we will also learn how the lipid molecules play roles in the formation and function of the thylakoid membrane, by extracting the lipids from the thylakoid membranes isolated from different development stages and identifying the lipid composition and content. If we can gain advanced understanding as to how thylakoid membranes are assembled we will be in a better position to modify the thylakoid membrane function, for example, to produce hydrogen from solar energy. In the long-term we may even be able to induce the production of similar membrane systems in different kinds of bacteria, giving us a new tool for the generation of microbial 'cell factories'.