Bio-desalination: from cell to tap

虽然地球表面的四分之三被水覆盖，但几乎所有的水都存在于海洋中，只有不到0.5%的淡水可用。不断增长的全球人口、工业化，尤其是农业，对这种有限的资源构成了巨大的压力。为了开发海洋中的巨大水资源，一段时间以来，人们的注意力一直集中在潜在的海水淡化以提供淡水上。然而，目前基于物理化学过程的海水淡化技术是一种对能源要求很高的过程，其应用仅限于燃料丰富的和/或富裕的发达国家。在这个项目中，我们转向从海水中去除氯化钠(氯化钠)的生物机制(生物淡化)。我们将利用海洋生物利用耗能的运输过程来维持细胞内低钠浓度的事实。这种自然淡化的能量最终来自海洋食物链底部的光自养生物收集的阳光。基于单个转运蛋白的离子通量速率及其在细胞膜中的丰度的现有信息，并考虑到高密度细菌培养产生的总细胞表面积和体积，我们建议将微生物培养物的低钠内部体积作为离子交换器，从周围的海水中去除氯化钠。在一个由来自不同学科(微生物学、生物物理、分子生物学、环境工程和过程工程)的专家团队领导的多管齐下的综合工作计划中，我们将开发生物工具，使我们能够控制海洋细菌的膜运输，我们将设计一个简单而节能的生长过程。暴露和清除海水中的细菌培养物。我们会透过人员交流计划、社会影响评估，以及由发展中国家水务行业和慈善机构的代表组成的谘询委员会参与，进一步发挥这项创新和多学科计划的培训潜力和潜在影响。工作包括五项工作：1.我们会选择合适的海洋蓝藻菌株，并找出可作为内源钠输出的开关触发点的环境条件(例如酸碱度、碳供应)。2.我们将调节光能、视网膜氯泵和钠通道蛋白的活性和生物物理性质，以产生一个功能性的积盐蛋白，以便在可诱导启动子的控制下在蓝藻中随后表达。3.我们将分析环境条件(包括盐度)对细胞壁的化学和物理性质的影响，并制定一种可控的细胞聚集方案，以促进从淡化水中快速去除蓝藻。4.我们将组装一个结合生物淡化不同生物阶段的原型工艺工程解决方案，并建立一个小试模型。5.我们将对这项新技术的社会影响、需求、风险和政策影响进行彻底评估。该项目解决了现代生物学和工程学不同领域的几个基本挑战。近年来在合成生物学和生物反应器技术方面取得的突破性进展为应对这些挑战创造了一个令人兴奋的研究环境，现在有现实的成功机会。此外，生物海水淡化技术还可与收获的微生物的下游工业用途相结合，例如生产生物燃料和提取用于化妆品和药品的生物化合物。对社会的潜在好处是显而易见的，因为拟议的技术获取了包裹在自养海洋生物、生物膜和离子梯度中的巨大能量。

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.