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

Abstract

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 (β-phellandrene) hydrocarbons in the unicellular cyanobacteria Synechocystis sp. PCC 6803. Heterologous expression of a codon-optimized Lavandula angustifolia β-phellandrene synthase (β-PHLS) gene in Synechocystis enabled photosynthetic generation of βphellandrene in these microorganisms. β-phellandrene accumulation occurred constitutively and in tandem with biomass accumulation, generated from sunlight, CO 2 , and H 2 O. Results showed that β-phellandrene diffused through the plasma membrane and cell wall of the cyanobacteria and accumulated on the surface of the liquid culture. Spontaneous β-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 CO 2 , without a prior requirement for the harvesting, dewatering, and processing of the respective biomass.

Carbon partitioning to the terpenoid biosynthetic pathway enables heterologous β-phellandrene production in Escherichia coli cultures

“…It has commercial value as a key ingredient in medical, cosmetic and cleaning products, and potentially as a fuel (Martin et al 2012;Bentley et al 2013;Zerbe and Bohlmann 2014). Microbial production of β-phellandrene through metabolic engineering can provide a sustainable alternative by which to meet increasing product demand from the commercial sector.…”

“…2013), taking advantage of the cell's photosynthesisdriven metabolism. A positive aspect of microbial β-phellandrene production is the spontaneous and quantitative separation of the molecule from the biomass and the liquid culture (Bentley et al 2013;Formighieri and Melis 2014). Floating of the β-phellandrene on the surface of the liquid culture facilitates segregation and harvesting, a parameter that weighs heavily on the economics of a microbial production system.…”

Cyanobacteria: Promising biocatalysts for sustainable chemical production

“…Engineering of the whole pathway represents a method to overcome the inherent regulation of native pathways that may limit product yields. Production of larger isoprenoid compounds has been accomplished by introducing terpene synthases from plant or tree species to redirect isoprenoid intermediates to limonene, β-phellandrene, caryophyllene, bisabolene, farnesene, and squalene (63,(82)(83)(84)(85)(86).…”

Solar-to-fuel conversion in algae and cyanobacteria

“…Spontaneous separation of the product from the biomass and the aqueous culture alleviates undesirable product inhibition or toxic effects on cellular metabolisms. Moreover, as a culture surface fl oater molecule, it could be easily harvested from the extracellular liquid phase, a parameter that weighs heavily on the economics of a microbial production system (Bentley et al 2013 ). However, terpene yields are much lower than those obtained for other heterologously produced metabolites (Table 7.1 ).…”

“…However, terpene yields are much lower than those obtained for other heterologously produced metabolites (Table 7.1 ). Normally, 80-85 % of photosynthetic carbon allocation is directed to sugar biosynthesis, 10 % to fatty acid and lipid biosynthesis, while only 3-5 % is directed to terpenoid biosynthesis (Melis 2013 ). Lower yields in heterologous terpenes, compared to alcohols or fatty acids in genetically modifi ed cyanobacteria, are a consequence of strict regulation in the endogenous carbon allocation.…”