Chapter 19 - Photosynthetic conversion of CO2 and H2O to long-chain terpene alcohol by genetically engineered N2-fixing cyanobacteria

Abstract

Biorefineries release one third of the carbohydrate carbon as CO2 during fermentation, as well as significant amounts of heat energy. For example, a 100 million gallons per year ethanol plant releases over 23 tons/h. of CO2 and 350 million BTU/h of heat. Ideally, a photosynthetic organism could be engineered to convert these unused resources into high value chemicals. Unfortunately, the current microalgae production model suffers from technical challenges including the need to harvest cells, extract oil, and then convert the oil into a final product. We circumvented these challenges to genetically engineer N2-fixing cyanobacteria as a living cellular factory to directly produce and secrete linalool (C10H18O) using CO2, atmospheric dinitrogen (N2) gas and H2O as the feedstock. Linalool is a volatile, fragrant alcohol emitted from many flowers and spice plants. Linalool has a wide range of applications such as manufacturing perfumes, fragrant hygiene products, flavors & fragrances. More importantly, linalool (a long-chain alcohol) has a high energy density and properties suitable for “drop-in” replacement for advanced biofuels or jet fuel. Cyanobacteria, like plant plastids, have the MEP pathway to produce geranyl diphosphate (GPP), the immediate precursor for production of linalool. However, cyanobacteria lack the linalool synthase that plants use to convert GPP into linalool. In this chapter, we introduced an isoprenoid biosynthetic pathway, the MEP pathway and then a plant linalool synthase gene was introduced into a nitrogen-fixing cyanobacterial strain Anabaena sp. PCC 7120 for photosynthetic production of long-chain terpene alcohols. A plant linalool synthase gene was driven by a synthetic dual native promoter (Pnir-PpsbA1) of Anabaena. The plant linalool synthase was overexpressed in transgenic Anabaena in which linalool was photosynthetically produced and secreted using CO2, N2 and H2O as feedstock.