Paradigm of Monoterpene (β-phellandrene) Hydrocarbons Production via Photosynthesis in Cyanobacteria

A direct "photosynthesis-to-fuels" approach envisions application of a single organism, absorbing sunlight, photosynthesizing, and converting the primary products of photosynthesis into ready-made fuel. The work reported here applied this concept for the photosynthetic generation of monoterpene (beta-phellandrene) hydrocarbons in the unicellular cyanobacteria Synechocystis sp. PCC 6803. Heterologous expression of a codon-optimized Lavandula angustifolia beta-phellandrene synthase (beta-PHLS) gene in Synechocystis enabled photosynthetic generation of beta-phellandrene in these microorganisms. beta-phellandrene accumulation occurred constitutively and in tandem with biomass accumulation, generated from sunlight, CO2, and H2O. Results showed that beta-phellandrene diffused through the plasma membrane and cell wall of the cyanobacteria and accumulated on the surface of the liquid culture. Spontaneous beta-phellandrene separation from the biomass and its removal from the liquid phase alleviated product inhibition of cellular metabolism and enabled a continuous production process. The work showed that oxygenic photosynthesis can be directed to generate monoterpene hydrocarbons, while consuming CO2, without a prior requirement for the harvesting, dewatering, and processing of the respective biomass.