CYANOBACTERIA, TERPENE "FACTORIES"?
For several years, Franck and Corinne Chauvat's team has been interested in the potential of cyanobacteria, photosynthetic microalgae that colonize most of our planet's ecosystems, for the photosynthetic production (capture of CO2) of terpenes, organic compounds of interest that can be used in the pharmaceuticals and cosmetics industry, biofuels or bioplastics (see November 2020 news). Their search for the ideal cyanobacterial strain for such applications led them i) to use the robust cyanobacterium Synechocystis PCC 6803, for which they developed powerful tools for heterologous gene expression, and ii) to explore its ability to produce various, chemically different, terpenes.
PUBLICATION 1
In publication #1, the researchers performed for the first time the engineering and comparative analysis of Synechocystis PCC 6803 for the photosynthetic production of limonene and pinene, two 10-carbon monoterpenes, and bisabolene, farnesene and santalene, three 15-carbon sesquiterpenes. The 5 terpene-producing strains are robust and genetically stable. Synechocystis PCC 6803 efficiently and stably produces farnesene and santalene, which is totally unprecedented for this model organism as well as for any other cyanobacteria, to date. The authors also showed that Synechocystis PCC 6803 efficiently produces terpenes when nitrate, the usual source of nitrogen for cyanobacteria, is replaced by urea, which should save costs for future industrial production or combine production and depollution.
PUBLICATION 2
In publication #2, the researchers questioned the involvement of CP12, a protein that regulates CO2 assimilation in photosynthetic organisms via the Calvin-Benson-Bassham (CBB) cycle, in terpene production in Synechocystis PCC 6803. They showed that CP12 regulates the redox balance of NADPH that feeds the methylerythritol 4-phosphate (MEP) pathway at the origin of the synthesis of terpene synthase substrates: geranyl diphosphate (GPP) and farnesyl diphosphate (FPP). In the absence of CP12, the production of both types of terpenes is increased in cyanobacteria expressing the corresponding terpene synthase. Interestingly, the authors report that, contrary to what was expected, CP12 is not required for growth under photoautotrophy in continuous light and under light/dark cycle, whereas it is essential for glucose catabolism that supports growth in the absence of photosynthesis.
The results of these two publications show that Synechocystis PCC 6803 is a robust "toolbox" for optimal photosynthetic production of terpenes, a class of hydrocarbons with multiple properties
Contacts :
Publication 1 : Franck Chauvat (franck.chauvat@cea.fr ; franck.chauvat@i2bc.paris-saclay.fr)
Publication 2 : Corinne Cassier-Chauvat (Corinne.Cassier-Chauvat@cea.fr ; corinne.cassier-chauvat@i2bc.paris-saclay.fr)
Inspired from : https://www.i2bc.paris-saclay.fr/news-2022/#news86 and https://www.i2bc.paris-saclay.fr/news-2022/#news79
During photosynthesis, CO2 is assimilated by the Calvin-Benson-Bassham (CBB) cycle, whose enzymes are inhibited during the light-to-dark transition and activated during the dark-to-light transition. CP12, an intrinsically disordered protein (without a stable three-dimensional structure) has two pairs of cysteines that form disulfide bridges in the dark and induce the formation of a complex structure of CP12 with two key CBB enzymes that become inactive. This regulation is rapid, which gives the CO2 fixation metabolism a strong plasticity.