Photons to fuels: Cyanobacterial cell factories for the production of terpenoid hydrocarbons
Terpenoids represent the largest and most diverse group of naturally occurring organic compounds. They are created by the action of terpene synthase enzymes, which catalyze complex rearrangements of carbon skeleton precursors to yield thousands of unique chemical structures that range in size from the simplest five carbon isoprene unit to the long polymers of rubber. Such chemical diversity has established terpenoids as valuable commodity chemicals with applications in the pharmaceutical, nutraceutical, cosmetic, and food industries. More recently, terpenoids have received attention as a renewable alternative to petroleum-derived fuels and as the building blocks of synthetic biopolymers. However, the current plant- and petrochemical-based supplies of commodity terpenoids have major limitations. Photosynthetic microbes present a promising platform to generate terpenoids in a renewable manner, employing a single organism that acts as both the photocatalyst and producer of ready-made fuels, and requiring only solar energy, water and carbon dioxide as the primary inputs. This talk will describe how we have applied and validated the concept of ‘photosynthetic biofuels’ upon the genetic engineering of cyanobacteria to confer the ability to produce terpenoid hydrocarbons of varying carbon chain length. Metabolic engineering strategies that successfully increase metabolic flux towards terpenoids and their precursors will be presented, including the elimination of competing metabolic sinks and the insertion of a non-native terpenoid pathway to bypass native regulatory mechanisms. Finally, the challenges associated with translating laboratory research to scalable industrial systems will be discussed in light of recent large-scale cultivation trials performed in photobioreactors and open raceway ponds at the US Department of Energy algal testbed in Arizona.