Regulation of polyphosphate metabolism in Chlamydomonas and potential for exploitation as P phosphorus sink in nutrient recovery systems

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Phosphorus is an essential element for life. It is a component of our genetic information (DNA and RNA). It plays critical roles in many aspects of our metabolism including the major energy currency of our cells ATP. It is a component of the membranes which surround our cells. It cannot be substituted for any other element. We obtain our phosphorus from our diet in the form of phosphate (phosphorus bonded to four oxygen atoms). Phosphorus enters the food chain through the acquisition of phosphate from the soil by plants. Plants, like all forms of life require this element and as any gardener knows it is one of the important macronutrients for plant growth- the P in your NPK fertiliser. Although it is quite an abundant element, most of the phosphorus in the environment is not in a form that plants can readily make use of (i.e., as soluble phosphate). Much of the phosphorus is locked in organic matter in the soil or bound to the surface of soil particles. This is why to get a good crop yield gardeners and farmers apply phosphate containing fertiliser. However there is a two-fold problem. To meet current needs rock phosphate is processed into phosphate fertiliser, but this non-renewable resource is being used and not replaced. At current rates of usage we will run out in between 50 and 200 years, so business as usual is not an option if we want to feed our children's children. The other problem is a more immediate one; much of the phosphorus we do use is wasted. Some of it enters water courses as agricultural run-off and can cause algal blooms in rivers and lakes. Much of it ends up at sewage works in domestic waste water from urine, faeces, organic waste and detergents. Because of strict environmental regulations on water quality, removing the unwanted phosphorus is necessary and expensive, contributing to high water bills. Use of chemicals to precipitate the phosphorus is a common method but limits reuse as a fertiliser. Biological methods are also used, and this is an active area of current research, but so far none have truly solved the problem of recovering phosphorus in an economic and re-usable way. This proposal is to investigate the fundamental mechanisms by which a species of alga called chlamydomonas, a microscopic unicellular photosynthetic organism, take up and store phosphate. Chlamydomonas is naturally occurring in the UK and grows well on waste water using either organic compounds in the waste, or light, to provide energy. It can accumulate phosphate to potentially high levels but the mechanisms by which it does so are not fully understood. To be able to use chlamydomonas or other naturally occurring algae to clear up waste water efficiently and recycle the reclaimed phosphate as fertiliser we need to understand what these mechanisms are and how and when they operate. The aims of our project are 1) to look at the effect of changing expression of genes that are thought to be involved in phosphate accumulation and storage to understand their role and importance in this process; 2) to test an hypothesis about the function of a gene of currently unknown function whose mutant phenotype implicates it in phosphate metabolism and 3) to find out which genes are important by looking for mutants which hyper accumulate phosphate. This fundamental knowledge will help engineers to design low-cost, low-carbon and environmentally friendly systems for phosphate recovery at sewage treatment works for sustainable reuse in agriculture.