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Revision as of 14:33, 18 September 2012


Synechosunshine: photosynthetically powered biolamp

The project we have been developing during these three months is base on an artificial consortium between two naturally coexisting microorganisms: Synechococcus elongatus PCC 7942 and Aliivibrio fischeri. Our main aim is the creation of an autosufficient biolamp powered by solar light. S. elongatus is a photosynthetic cyanobacteria, meanwhile A. fischeri is a marine heterotrophic bacterium, capable of producing bioluminescence after quorum sensing signals.

We choose Synechococcus because of its great photosynthetic capacity due to its size and alometry, despite it is difficult to transform its complicated genome (8 different plasmids with genes unrepeated!!). (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 couterillumination. Coevultion of A. fischeri with other species is very habitual. We have tried to arrange an artificial symbiotic interaction (communication and feeding) between these two organisms (co-cultured 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 auto secreted 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 are modifying 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 promoter 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 (Biobrick from the parts registry), before ligating the luxI gene.

An important part of our aim 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. from the Wyss Institute of Biologically Inspired Engineering (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 auto sustainable, as the energy captured from the sun by S. elongatus is exported for A. fischeri to use it.

Other Ideas

Other parallel objective included transforming Chlamydomonas reinhardtii with a DNA gun to introduce the whole lux operon from Aliivibrio in the chloroplast’s genome, to render it bioluminescent. The transformation of an eukaryotic autotroph could be the first step towards bioluminescent vascular plants, which could be easily used as environmentally friendly street lighting, despite being in theory less efficient than our symbiotic system, due to their robust physiognomy and little optimization for luminescent and photosynthetic functions. On the other hand, plants would be a more handy option, due to their environmental resistance and independence of a careful and constant upkeep.