Norman Hascoe Distinguished Lecture Series
Center for Bioenergy and Photosynthesis, Department of Chemistry and Biochemistry, Arizona State University
Imagine* Photosynthesis Where Human Ingenuity Supersedes Evolution(*John Lennon)
Operating at ~ 133 TW, photosynthesis powers the biosphere and is fully booked providing biosphere service and support. Anthropogenic activity takes a cut of the 133 TW with crop photosynthesis today being driven by unsustainable agricultural practices to produce food and limited bioenergy for human use. In fact, there are no reserves of photosynthetic capacity to provide food for the ever-increasing human population and to meet the added burden of biofuel for growing our GDP. Indeed, when such demands are made the capacity comes at the peril of biosphere service and support, pushing the planet further from a sustainable trajectory. Fortunately, photosynthesis can be dramatically improved to meet human needs. The theoretical limit to solar energy conversion efficiency is set by fundamental thermodynamic principles that apply to the isothermal conversion of light into chemical and/or electrical potential. Photovoltaic technology uses these principles combined with advances in materials to achieve record efficiencies of solar to electrical power conversion. Photosynthesis, having been optimized by Darwinian selection to move genes forward, is not optimal for providing solar-derived fuel to support human activities. Measured against the conversion efficiency of PV-driven electrolysis, the less-than-optimal efficiency of photosynthesis is obvious and starts with a poor match of the absorption of light by photosynthetic organisms to the solar spectrum. In selected photosynthetic systems, rational design, based on the principles demonstrated in artificial systems and the techniques of molecular and synthetic biology, can be used to optimize solar-to-biofuel conversion efficiencies to meet particular needs. Key biological systems necessary to initiate this research are found in extant photosynthetic organisms. My lecture will draw attention to opportunities for far-reaching research and will cover our progress using fundamental design principles and technology to inspire the design of high efficiency artificial and natural photosynthesis. This work includes the design of low and high potential artificial reaction centers with appropriate antenna systems arranged in a tandem, two-junction configuration to oxidize water and reduce protons to hydrogen. Several water oxidation catalysts are being used at the high potential junction and work describing the use of hydrogenase enzymes at the low potential junction will be described. Related work will be presented on the role of model systems in unraveling the mechanism whereby carotenoid pigments control 133 TW of photosynthetic power flow. Understanding control systems is key to re-engineering photosynthesis. The combination of technology with rationally designed biology can be a step towards achieving sustainable energy production based on efficient solar-driven water oxidation and proton and/or carbon reduction.