Production of lignofuels and electrofuels by extremely thermophilic microbes

Abstract

Extreme thermophiles are microorganisms that grow optimally at elevated temperatures (≥ 70°C). They could play an important role in the emerging renewable energy landscape by exploiting thermophily to produce liquid transportation fuels. For example, Caldicellulosiruptor species can grow on unpretreated plant biomass near 80°C utilizing novel multi-domain glycoside hydrolases. Through metabolic engineering, advanced biofuels compatible with existing infrastructure liquid biofuels, so-called lignofuels, could be produced to establish consolidated bioprocessing at high temperatures. In another case, a new paradigm, electrofuels, addresses the inefficiency of biofuel production through the direct synthesis of advanced fuels from carbon dioxide using hydrogen gas as the electron carrier. This requires coupling of biological electron utilization to carbon dioxide fixation and ultimately to fuel synthesis. Using a hyperthermophilic host Pyrococcus furiosus and synthetic metabolic pathways comprised of genes from less thermophilic sources, temperature-regulated biosynthesis of industrial organic chemicals and liquid fuel molecules are possible. Herein, we review recent progress towards the synthesis of lignofuels and electrofuels by extremely thermophilic microorganisms.

Keywords:

• extreme thermophiles
• Pyrococcus furiosus
• Metallosphaera sedula
• Caldicellulosiruptor
• biofuels
• electrofuels
• CO₂ fixation
• lignocellulose

Acknowledgements

This work described here was supported in part by the US National Science Foundation (CBET-1264052 and CBET-1264053) and by the US Department of Energy (DOE) through the ARPA-E Electrofuels Program (DE-AR0000081), the Division of Chemical Sciences, Geosciences and Biosciences of the Office of Basic Energy Sciences (DE-FG05-95ER20175), and the BioEnergy Science Center (DE-PS02-06ER64304), a Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the DOE under Contract DE-AC05-00OR22725.