CYAO Project: Brief Synopsis.
Aquatic photosynthetic unicellular organisms are perceived as one of the most viable sources for the implementation of sustainable alternative fuel production and implantation of green chemistry. Amongst them, the prokaryotic cyanobacteria appears particularly appealing because they are generally well characterised, have plain nutritional requirements and posses large genetic diversity. Nevertheless, their industrial potential is still relatively unexplored. One of the main factors negatively affecting biomass production of photosynthetic organisms grown in photobioreactors is culture self-shading at high cell densities. As a consequence of this, the light that penetrates through the culture layers is significantly dimmer than at the surface, therefore most of the culture is exposed to suboptimal lights regimes. The strategy we propose is centred on the modification of the well characterised species Synechocystis sp. PCC6803, which was already proven to have biotechnological potential, which will affect the light harvesting capiacity by methabolic engineering of chlorophyll, the main photosynthetic pigment, biosynthetic pathway. The spectral reshaping of light absoprtion will be controlled so that is activated by the light conditions themselves as soon a the screening becomes significant. The species will presumably display a significant improvement in growth yield under bioreactor relevant conditions. Thereby they should also be considered as an ideal platform to introduce modifications tailored to exploit their metabolic flexibility. In this context we propose two different strategy to test the productivity of the newly engineered variant. One, is to use cyanobacterial cell, per se, as a source of lipids for bio-diesel production, since their lipidome fully resemble the one of the commonly employed seed oil. The second, and more intriguing, involves metabolic engineering leading to the production of specific carotenoids, which have widespread applications as nutritional supplements, antioxidants and natural colorant (biocolorant). In particular we propose to produce variants that accumulate astaxanthin and/or canthaxantin, two carotenoids that have relevant economic importance because they are used as an additive by both salmon and trout breeders to increase the value of the final products and represent one of the main industrial costs. A cheaper, and readily available source of astaxanthin and cantaxanthin is envisaged to reflect positively on the economics of this industrial sector.