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We engineered a recombinant cyanobacteria to achieve “biodesalination”, which is to extract sodium chloride from seawater through biological membranes. There are already some methods to convert saltwater into freshwater, such as distillation and reverse osmosis. However, the high energy consumption of these technologies has significantly limited their scale of application. Therefore the development of an innovative, low-energy biological desalination process by biological membranes, would be very attractive. Cyanobacteria have several characteristics which make them an ideal organism for biodesalination: fast-growing, photoautotrophy, amenable to genetic transformation and able to grow over a wide range of salt concentrations. Halorhodopsin, a light-driven inward-directed chloride pump from halobacteria, confers cyanobacteria the ability to absorb chloride to a large extent if functionally expressed in cyanobacteria. And we propose that the negative membrane potential generated by halorhodopsin would drive the influx of cation through ion channels.
Together with the biodesalination driver halorhodopsin, we have inducible expression systems, which could be regarded as the biodesalination controller. We apply light-inducing systems to avoid any bad effect on water of chemicals and heavy metals, which are widely used in synthetic biology of cyanobateria. The PcpcG2 is a green-light inducing promoter, which has been characterized and proved to be a useful genetic tool; the Pdark is induced by darkness and is from the idea of previous iGEM team. The cultivation of engineered cyanobacteria comprises three phases: growth phase, expression phase and desalination phase. After cyanobacteria reaching a high density, we induce the expression of halorhodopsin, and we move the cyanobacteria into white-light condition afterwards, which allows the halorhodopsin to work.
August 26th Yin Can
