The phycobilisome; how can light energy be converted to chemical energy with 95% efficiency?

With fossil fuel supplies decreasing and global warming effects growing, solar energy is increasingly in demand. However, current solar panel efficiency is low with solar panels on most homes in the UK operating at only 15-20% efficiency. Red microalgae, in contrast, achieve 95% efficiency through their photosynthetic machinery, termed phycobilisomes. Harnessing these molecular systems for renewable energy applications has tremendous potential for the biotechnological industry. However, first we need to know what these phycobilisomes are made of and, thus, what makes these biological machines operate with such high efficiency.

This research proposal will, for the first time, use state-of-the-art mass spectrometry to characterise the phycobilisome in red microalgae. By addressing this research question from an entirely new angle, we will deepen our understanding of how the phycobilisome is constructed. The phycobilisome efficiency will be altered by changing the light conditions during microalgae growth. By tracking the structural features of the phycobilisome with photosynthetic efficiency, we will determine the critical factors that are necessary for efficient light transmission and as such determine which phycobilisome composition is the most efficient for photosynthesis. The findings of which are essential to allow us to construct these highly efficient microscopic machines for incorporation into solar panel devices.

The results of this proposal will have broad impact in the academic community amongst structural biologists, mass spectrometrists and within the solar energy and microalgae communities, with any knowledge gained being rapidly translatable for industrial use.

Using solely renewable energy is a dream. One of its major sources, solar panels, meets only 4% of our energy needs, operating at a mere 15-20% efficiency. In nature, microalgae have 'solar panels', termed phycobilisomes, that operate at <95% efficiency without requiring direct sunlight. Incorporating phycobilisomes into solar panels for more effective light transfer is an innovative way forward, but knowledge as to how microalgae transmit light effectively is limited. Characterisation of phycobilisomes is challenging due to their dynamic nature and large size (17 MDa). Phycobilisomes contain >800 protein subunits that assemble into hexameric sub-complexes linked together by specific linker proteins. X-ray crystallography has enabled structures of the sub-complexes to be determined, however, information on the linker proteins was lacking. More recently, cryoEM data on the intact phycobilisome has provided additional structural information on the linker proteins, thus a potential light transmission mechanism has been proposed. A single snapshot of the phycobilisome, however, only infers how light is transferred at that specific moment in time. Moreover, since microalgae adapt their photosynthetic efficiency based on their environment, the structures available may represent anything from the least efficient to the most efficient energy transfer path. In addition, details are still lacking in flexible, dynamic regions of the complex.

We will use a mass spectrometry (MS) approach to fully characterise the phycobilisome. By combining new, state-of-the-art native MS, cross-linking MS, top-down and bottom-up proteomics technology, we will reveal additional new structural features of the phycobilisome that are strictly necessary for light transmission. Finally through tracking how these structural components of the phycobilisome change in response to photosynthetic efficiency, we will reveal the important factors behind these 95% efficient microalgae 'solar panels'.

The phycobilisome converts light energy to chemical energy six times more efficiently than anything humans can currently engineer. How this system in algae has evolved to do this is remarkable. Our research seeks to understand how this phycobilisome in algae operates with such high efficiency; a finding that will translate into our ability as engineers to design highly efficient artificial photosynthetic machinery for use in future solar panels. Through dissemination of our findings, both individuals, organisations and society will benefit.

Who will benefit?

The beneficiaries of this research proposal are the energy industry, the algae biotechnology industry, mass spectrometry manufacturers and society in general.

How will individuals, organisations and society benefit?

Energy Industry: Innovative ways to harness solar energy are needed to greatly enhance solar panel efficiency. Microalgae have been evolving for billions of years to transmit light effectively enabling them to survive in dimly lit climates. This research will provide significant insight into the energy transmission process. The findings could be used to generate new materials for incorporation into solar panels. Moreover, microalgae offer a significant advantage over other raw materials since they are effectively carbon neutral.

Algae Biotechnology Industry: The products of microalgae have many applications; red dye in the cosmetic industry, blue food colouring, omega-3 fatty acid production within the food industry and biofuel production. In addition, microalgae have been reported to produce bioactive compounds with anticancer, antifungal, anti-inflamatory, antibacterial and antioxidant activity. Scaling up microalgae growth to produce these products can be challenging. Our research will provide a more in-depth knowledge on how microalgae photosynthesise and thus help provide solutions for optimum microalgae growth. Moreover, by ensuring optimal microalgae growth conditions, microalgae will produce their desirable products extremely effectively.

Mass Spectrometry Manufacturers: Demonstrating new applications of the latest technology in new research areas is the first and foremost step in ensuring new technology reaches its maximum potential. This research will showcase how mass spectrometry can be used to gain structural insights into photosynthetic research. Once the methodology is established, these methods will be widely applicable for the analysis of other photosynthetic complexes. This will bring revenue for the mass spectrometry industry. Moreover, through collaboration with Thermo Fisher Scientific, any specific requirements for these types of analysis will be readily incorporated into the next generation instruments enabling more potential for new applications of the technology.

Societal impact: From advances in our ability to scale up the production of microalgae products (detailed above), the nation will benefit in terms of their health and in wealth through the generation of jobs in the various industries. Society will also benefit from technological advancement and through the creation of highly skilled researchers trained in specialised techniques whose expertise could then be applied to solve a variety of pressing scientific problems.

The BBSRC will benefit from this internationally competitive research; this project addresses questions that are important globally and will accelerate technological development. The research falls under several of the BBSRC strategic priority areas; technology development for the biosciences, new strategic approaches to industrial biotechnology, data driven biology and bioenergy and generating new replacement fuels for a greener, sustainable future.