Researchers at the University of Liverpool and collaborators have discovered new understanding of bacterial photosynthesis.

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Source: Professor Luning Liu, Chair of Microbial Bioenergetics and Bioengineering, University of Liverpool

A unique ‘flat’ dimeric structure of bacterial photosynthetic reaction centre-light harvesting membrane complexes discovered by state-of-the-art cryogenic electron microscopy.

Using cutting-edge techniques, investigators have unveiled intricate detailed images of the key photosynthetic protein complexes of purple bacteria. These images shed new light on how these microorganisms harness solar energy.

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The study, published in Science Advances, not only advances scientists’ understanding of bacterial photosynthesis but also has potential applications in the development of artificial photosynthetic systems for clean energy production.

Bacterial photosynthesis

Like plants, many bacteria have evolved the remarkable ability to convert light into energy through a process called bacterial photosynthesis. This important biological reaction enables the microorganisms to play a crucial role in global nutrient cycles and energy flow in ecosystems and form the base of aquatic food chains. Studying ancient bacterial photosynthesis also helps to understand the evolution of life on Earth.

This latest work presents high-resolution structures of photosynthetic reaction centre−light harvesting complexes (RC−LH1) from Rhodobacter blasticus, a model organism for understanding bacterial photosynthesis.

The research team of collaborators from the University of Liverpool, the Ocean University of China, Huazhong Agricultural University and Thermo Fisher Scientific, captured detailed images of both monomeric and dimeric forms of the RC-LH1 membrane protein supercomplexes. These structures reveal unique features that distinguish R. blasticus from its close relatives, highlighting the remarkable variability in photosynthetic systems among purple bacteria.

Light-harvesting

Professor Luning Liu, Chair of Microbial Bioenergetics and Bioengineering, University of Liverpool said: “By revealing these natural photosynthetic mechanisms, we open new avenues for designing more efficient light-harvesting and energy transduction systems or cells. This study represents a significant step forward in our comprehension of how bacteria optimize their photosynthetic machinery, providing valuable insights that could inform future clean energy innovations.”

A unique feature of the RC-LH1 dimer of R. blasticus is its flatter conformation compared to its counterparts from other model species. This structure provides the foundation for specific membrane curvature and energy transfer efficiency in bacteria.

Unlike some related bacteria, R. blasticus lacks a protein component called PufY in the RC-LH1 structure. The study revealed that its absence compensates with additional light-harvesting subunits that create a more enclosed LH1 structure. This was determined to affect electron transport rates of the RC-LH1 structure.

Evolutionary adaptations

This systematic study, integrating structural biology, in silico simulations, and spectroscopic studies, provides new insights into how bacterial photosynthetic complexes assemble and mediate electron transfer, crucial processes for energy production.

Lead researcher, Professor Luning Liu added: “Our findings demonstrate the structural diversity of photosynthetic complexes even among closely related bacterial species. This variability likely reflects different evolutionary adaptations to specific environmental conditions. We are thrilled that we can contribute such molecular details in the investigation of photosynthetic mechanisms and evolution.”

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