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Synechosunshine: photosynthetically powered biolamp

Our main goal for iGEM 2012 is the creation of an autosufficient 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 chose Synechococcus because of its great photosynthetic capacity due to its size and alometry, even though it is difficult to transform due to its complicated genome (it has 8 different plasmids with unrepeated genes!!). (foto nuestra coccus)

On the other hand, Aliivibrio is a gammaproteobacterium which has stablished symbiosis with other marine organisms, exchanging bioluminescence for glucidic nutrients. The best known example for this is the bobtail squid Euprymna scolopes, which uses Aliivibrio grown in ventral photophores for nocturnal counterillumination. Coevultion of A. fischeri with other species is very habitual.

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 point of making a biphasic setting is to avoid interference in the light emission-absorption between the different cultures to enhance the general energetic efficiency of the system. (foto de aliivibrio brillando)

A. fischeri’s genes for bioluminescence are regulated by an operator which only activates at high concentrations of AHL (Acyl-homoserine-lactone), an autosecreted quorum sensing molecule which occurs abundantly at high population densities (aggregated in colonies, biofilms, host glands or phycospheres). When it lives free in the water it does not express bioluminescence.

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. 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. (2010) from Harvard University, which was transformed with a gene which expresses a transporter protein (cscB) to export sucrose to the culture medium in the presence of salt. This is how we render our biolamp autosustainable, as the energy captured from the sun by S. elongatus is exported so that A. fischeri can use it.