Engineering of polychromatic photosystems for expanded solar energy conversion

Abstract

Photosynthesis provides the mechanisms through which sunlight powers most of our biosphere. Either through direct application or inspiration, natural solar energy conversion strategies offer mankind potential solutions to impending energy and food crises through the exploitation of free solar power. However, the overall efficiency of photosynthesis is limited by a variety of factors including the selective light spectral coverage displayed by the choice of major pigments. Intriguingly, the complementary absorption profiles of chlorophyll-based photosystems and bacteriochlorophyll-based photosystems from oxygenic or anoxygenic phototrophs provide a pathway toward enhanced light capture across the photosynthetically-useful spectrum by synthetic biology. The research described in this thesis explores the effectiveness of a range of linking strategies to assemble bacteriochlorophyll-containing reaction centers (RC) and chlorophyll-containing light harvesting complexes (LHCs) into single polychromatic photosystems. Among the all biological strategies, a SpyTag/SpyCatcher linker offered the most effective way to form macromolecular “chimeras” between the RC from photosynthetic bacterium Rhodobacter sphaeroides and LHCs from Arabidopsis thaliana. Energy transfer from LHC to RC was confirmed both in solution and on an electrode and the current output of bacterial-RC photoelectrodes was shown to benefit from light capture by LHCs. In parallel, synthetic optically-active quantum dots (QDs) were shown to act as hubs for the self-assembly of LHC/RC/QD conjugates and to act as an energy bridge to augment direct LHC to RC energy transfer. A tight-binding interface between proteins and QDs was characterized. Based on the in-depth understanding of thermodynamics of this photosystem, it was found that energy flow within the tri-component conjugates could be tuned in a manner similar to natural photosystems and to a comparable level of efficiency. The project demonstrated the power of applying synthetic biology principles to the systematic redesign of natural photosynthesis and the expansion of solar energy conversion beyond the natural boundaries of living systems.

Date of Award	25 Jun 2019
Original language	English
Awarding Institution	University of Bristol
Sponsors	Engineering and Physical Sciences Research Council & Biotechnology and Biological Sciences Research Council
Supervisor	Michael R Jones (Supervisor) & Dek N Woolfson (Supervisor)