Team:SJTU-BioX-Shanghai/Description

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This year, we will engineer a recombinant cyanobacteria to achieve “biodesalination”, which means 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 limited their application. Therefore the development of an innovative, low-energy biological desalination process, by biological membranes of cyanobacteria, would be very attractive. Many cyanobacteria possess salt-tolerance mechanisms, among which sodium export is the most important one. Halorhodopsin is a light-driven inward-directed chloride pump from halobacteria. We will functionally express it in cyanobacteria to drive influx of chloride together with sodium, thus conferring cyanobacteria the ability to absorb salts to a significant degree.

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 et al. The cultivation of engineered cyanobacteria is proposed to comprise two phases: growth phase and desalination phase.

Cyanobateria should grow to reach a high density before beginning to express chloride pump halorhodopsin and absorb salts into the cells. What’s more, inhibition of photosynthetic ATP should be achieved to halt sodium export. Therefore an inducible dark –sensing promoter, is vital to the achievement of biosesalination. Based on an idea of previous iGEM teams, We are modifying the promoter of cpcG2 to obtain a “dark-sensing” promoter. The “dark-sensing” promoter is a combination of the promoter of cpcG2 and a constitutive promoter. Green light induces CpcR to bind to a region of cpcG2, thus inhibiting RNA polymerase binding to the constituve promoter. Therefore darkness will allow the transcription of downstream gene. This is the principle of the “dark-sening” promoter.