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Synechosunshine: photosynthetically powered biolamp

Our main goal for iGEM 2012 is the creation of a self-sufficient biolamp powered by solar light. In order to do this we have taken advantage of an artificial consortium between two naturally coexisting microorganisms: Synechococcus elongatus PCC 7942 and Aliivibrio fischeri. A. fischeri is a marine heterotrophic bacterium, capable of producing bioluminescence after activation by quorum sensing signals, while S. elongatus is a photosynthetic cyanobacterium that will allow the system to be fed by solar light.

We have arranged an artificial symbiotic interaction (communication and feeding) between these two organisms (cocultured in common broth separated by a semipermeable membrane) by the means of genetic engineering. The reason behind the biphasic setting is to avoid interference in the light emission-absorption between the different cultures to enhance the general energetic efficiency of the system.

A. fischeri’s genes for bioluminescence are regulated by an operator which is only activated at high concentrations of AHL (Acyl-homoserine-lactone), an own secreted quorum sensing molecule which is abundantly present at high population densities (aggregated in colonies, biofilms, host glands or phycospheres). When this bacterium lives free in open waters it does not express bioluminescence (Miyashiro and Ruby, 2012).

To induce bioluminescence in our system, we have modified S. elongatus to synthesize and export AHL to the common broth, in order to induce bioluminescence in A. fischeri. As our biolamp only requires to be ‘switched on’ at night, we are preceding the gene expressing AHLase enzyme (luxI) with a photosensitive operator. The genetic construct is based on the cyanobacterial promotor psbAI, which responds to light through the molecular physiology of the cyanophyte photosystem (Golden, 1995). As we require an inverse response to light stress, we annexed the cI lambda inverter, before ligating the luxI gene.

An important part of our project was to use the photosynthetic organism as a chemical energy donor for the luminescent heterotrophic population. To achieve this, we used a strain of S. elongatus developed by Ducat et al. (2012) from Harvard University which was transformed with a gene that expresses a transporter protein (cscB) to export sucrose to the culture medium in the presence of salt. This is how we render our biolamp self-sustainable, as the energy captured from the sun by S. elongatus is exported so that A. fischeri can use it.

Ducat, D. C., Avelar-Rivas, A. J., Way, J. C. & Silver, P. A. (2012) Rerouting carbon flux to enhance photosynthetic productivity. Applied and Environmental Microbiology, 78(8):2660–2668.

Golden, S. S. (1995) Light-Responsive Gene Expression in Cyanobacteria. J. Bacteriology, 177(7): 1651-1654.

Miyashiro, T. & Ruby G. E. (2012) Shedding light on bioluminiscence regulation in Vibrio fischeri. Mol. Micro., 84(5):795-806.