Genetically engineering cyanobacteria to convert CO2, water, and light into the long-chain hydrocarbon farnesene

Abstract

Genetically engineered cyanobacteria offer a shortcut to convert CO2 and H2O directly into biofuels and high value chemicals for societal benefits. Farnesene, a long-chained hydrocarbon (C15H24), has many applications in lubricants, cosmetics, fragrances, and biofuels. However, a method for the sustainable, photosynthetic production of farnesene has been lacking. Here, we report the photosynthetic production of farnesene by the filamentous cyanobacterium Anabaena sp. PCC 7120 using only CO2, mineralized water, and light. A codon-optimized farnesene synthase gene was chemically synthesized and then expressed in the cyanobacterium, enabling it to synthesize farnesene through its endogenous non-mevalonate (MEP) pathway. Farnesene excreted from the engineered cyanobacterium volatilized into the flask head space and was recovered by adsorption in a resin column. The maximum photosynthetic productivity of farnesene was 69.1 ± 1.8 μg·L(-1)·O.D.(-1)·d(-1). Compared to the wild type, the farnesene-producing cyanobacterium also exhibited a 60 % higher PSII activity under high light, suggesting increased farnesene productivity in such conditions. We envision genetically engineered cyanobacteria as a bio-solar factory for photosynthetic production of a wide range of biofuels and commodity chemicals.

Isoprenoid-Based Biofuels: Homologous Expression and Heterologous Expression in Prokaryotes

“…MMPE utilizes partitioning of the overall DXP pathway into smaller modules, and components of each module are then tuned separately in order to obtain higher yields of the desired metabolites. Codon optimization has also provided a promising platform for the optimization of nonnative genes to enhance isoprenoid-based biofuel production in microbial hosts (11,37,59). However, the application of codon optimization is limited by inherent low enzyme activities and specificities of the isoprenoid pathways in microbial hosts.…”

“…Incorporation of the codon-optimized fs gene from P. abies in the filamentous cyanobacterium Anabaena sp. strain PCC 7120 enabled photosynthetic production of farnesene through an endogenous DXP pathway (59). The total photosynthetic accumulation of farnesene was ϳ305 g liter Ϫ1 during 15 days of growth, with specific farnesene productivity at ϳ20 g liter Ϫ1 optical density (OD) Ϫ1 day Ϫ1 (59).…”

“…Sesquiterpenes have been proposed as diesel fuels, and their estimated cetane value, cloud point, and energy density are also in the range of those of diesel fuels (2,7,15,75). Recently, metabolic engineering approaches have been utilized in cyanobacteria to exploit their ability to produce isoprenoids from H 2 O and CO 2 (simplest carbon source) (14,22,58,59). The advantages associated with cyanobacteria, such as fast growth compared to that of plants and yeast, high photosynthetic rate, genetic tractability, and sequenced genomes bring them to the forefront of biofuel research.…”

“…Strain engineering efforts have provided an array of new opportunities to engineer alternate microbial strains as hosts for the nonnatural production of isoprenoid-based biofuels (13,15,58,59). Engineering alternate microbial hosts also enables researchers to explore their ability to utilize a vast array of carbon sources for biofuel production.…”

“…Both enzymes have been introduced in microbes either with a heterologous MVA pathway (73,74) or with an optimized endogenous DXP pathway (13). Modulation of the DXP pathway in alternate microbial hosts, such as cyanobacteria, Corynebacterium glutamicum, and Streptomyces sp., has improved biofuel yields in such hosts (13,15,58,59). Combinatorial gene expression of Table 1).…”