Bio-desalination: from cell to tap

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While three quarters of the earth's surface is covered in water almost all of it is present in the oceans with less than 0.5 % available as freshwater. Increasing global population, industrialisation and particularly agriculture exert significant pressures on this limited resource. With the aim to unlock the vast water resource in the oceans, attention for some time has focussed on the potential desalination of seawater to provide freshwater. However, current desalination technology, based on physicochemical processes, is a highly energy demanding process and its application is limited to fuel-rich and/or affluent developed countries. In this project we turn to biological mechanisms to remove sodium chloride (NaCl) from seawater ('bio-desalination'). We will exploit the fact that marine organisms employ energy-consuming transport processes to maintain low sodium concentrations inside their cells. The energy for this natural desalination ultimately comes from sunlight harvested by photo-autotrophic organisms at the bottom of the marine food chain. Based on available information on ion flux rates through individual transport proteins and their abundance in cell membranes, and taking into account the total cell surface area and volume generated by high-density bacterial cultures, we propose that the energized low-sodium internal volume of microbial cultures can be used as an ion exchanger to remove NaCl from the surrounding seawater.In a multi-pronged, integrated work programme led by a team of experts from different disciplines (microbiology, biophysics, molecular biology, environmental engineering and process engineering) we will generate the biological tools that will enable us to control membrane transport in marine bacteria, and we will design a simple and energy-efficient process for growth, exposure and removal of the bacterial cultures in/from the seawater. We will further maximise both the training potential and the potential impact of this innovative and multidisciplinary programme through staff exchange programmes, Social Impact Assessment and involvement of an Advisory Board which includes representatives of water industries and charities working in developing countries.The work comprises five work packages: 1.We will select a suitable isolate of marine cyanobacteria and identify environmental conditions (e.g. pH, carbon supply) that can act as on/off triggers for endogenous Na-export. 2. We will adjust the activity and biophysical properties of light-energized, retinal Cl-pumps and Na-channel proteins to generate a functional 'salt-accumulator for subsequent expression in the cyanobacteria under the control of an inducible promoter. 3. We will analyse the effect of environmental conditions (including salinity) on chemical and physical cell-wall properties and develop a controllable cell-aggregation protocol to facilitate rapid removal of the cyanobacteria from the desalted water. 4. We will assemble a prototype process engineering solution that combines the different biological phases of bio-desalination, and we will build a bench-scale model. 5. We will carry out a thorough assessment of social impact, demands, risks and policy implications of this new technology. The project addresses several fundamental challenges in different areas of modern biology and engineering. The groundbreaking advances made over recent years in synthetic biology and bioreactor technology have created an exciting research environment for tackling these challenges now with a realistic chance of success. Furthermore, bio-desalination technology lends itself to be combined with downstream industrial uses of the harvested microorganism e.g. the production of bio-fuel and extraction of bio-compounds for cosmetics and medicine. The potential benefit for society is evident as the proposed technology harvests the enormous energy that is encapsulated in autotrophic marine life, biological membranes and ion gradients.