Scientists have made a fascinating discovery about archaea, single-celled microorganisms that are some of the oldest life forms on Earth. A research team from the University of Tokyo and Nagoya Institute of Technology has revealed a…
Rhodopsins: The Light-Harvesting Proteins of Marine Life
Scientists have made a fascinating discovery about archaea, single-celled microorganisms that are some of the oldest life forms on Earth. A research team from the University of Tokyo and Nagoya Institute of Technology has revealed a highly sensitive light-driven hydrogen ion pump found in a type of archaea called Heimdallarchaeota. Specifically, they’ve uncovered how some archaea harness light energy using carotenoid antennas, tiny light-harvesting structures. This research sheds light on the ancient evolution of phototrophy – the ability to use light for energy – and opens up exciting new possibilities for understanding life’s diversity.
Harnessing the Power of Light
Heimdallarchaeota, considered close relatives to the last common ancestor of eukaryotes (organisms with cells containing a nucleus, like plants and animals), were found to possess a unique protein called Heimdallrhodopsin. This remarkable protein utilizes carotenoid pigments—the same pigments that give many plants and fruits their vibrant colors—to efficiently capture solar energy. Importantly, this captured energy is then used to transport protons (H+), converting light energy into chemical energy.
A Unique Mechanism of Light Harvesting
What makes this discovery even more significant is the way Heimdallrhodopsin works. Using advanced laser spectroscopy, researchers demonstrated that the carotenoid pigments act as light-harvesting antennas, significantly boosting the efficiency of the proton pump. This was an unexpected find. Moreover, X-ray crystallography revealed a unique protein structure perfectly suited for binding various carotenoid pigments, further enhancing its light-capturing capabilities.
The study, published in Nature, focused on HeimdallR1, a type of rhodopsin – a light-sensitive protein – found in Candidatus Kariarchaeum pelagium, an archaeon. Rhodopsins are already known for their role in light-sensing and energy production in various organisms, but the discovery of their interaction with carotenoid antennas in archaea adds a new dimension.
HeimdallR1: A Unique Light-Harvester
What makes HeimdallR1 particularly interesting is its ability to bind to specific hydroxylated carotenoids like lutein, diatoxanthin, and fucoxanthin. These molecules efficiently absorb light in the violet and blue range, passing the energy onto the retinal chromophore of the rhodopsin, which then uses that energy to pump protons. This process generates an electrochemical gradient, essentially producing energy that the archaea can use. The protein’s unique structure, specifically a “fenestration” (an opening), facilitates this energy transfer. This unique mechanism expands our understanding of how energy transfer occurs in these ancient organisms.
The Evolutionary Significance of Carotenoid Binding
Furthermore, this discovery has important implications for our understanding of the evolution of phototrophy. The presence of this light-harvesting system in archaea, which are closely related to eukaryotes (organisms with complex cells), suggests that similar mechanisms may have played a role in the evolution of photosynthesis in more complex life forms. This opens up new avenues for research and could ultimately lead to the discovery of novel approaches for harnessing solar energy.
Expanding the World of Archaeal Rhodopsins
Interestingly, researchers found that HeimdallR1 isn’t alone. They discovered two more closely related rhodopsin families, further highlighting the diversity of these light-harvesting systems in marine environments. The researchers also observed that the genes responsible for the different rhodopsin variations show high diversity, suggesting potential gene exchange between different species. This emphasizes the dynamic nature of evolution and adaptation in microbial communities.
Beyond HeimdallR1: A Wider Perspective
The study also revealed that HeimdallR genes are widespread in various marine and estuarine environments. This wide distribution shows the important role that these light-harvesting systems play in marine ecosystems, a previously underappreciated contribution.
Reference
- Tzlil, G., Del Carmen Marín, M., Matsuzaki, Y., Nag, P., Itakura, S., Mizuno, Y., Murakoshi, S., Tanaka, T., Larom, S., . . . Béjà, O. (2025). Structural insights into light harvesting by antenna-containing rhodopsins in marine Asgard archaea. Nature Microbiology. https://doi.org/10.1038/s41564-025-02016-5
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Neha Adikane holds a Master’s degree in Environmental Science from Pune University, bringing a unique blend of scientific expertise and creative writing skills to her craft. She specializes in creating engaging, insightful, and impactful content across various niches. With a passion for translating complex ideas into simple, relatable narratives, she excels at crafting blogs, articles, website content, and social media posts that captivate readers and drive engagement. Neha’s background in environmental science adds depth to her writing, allowing her to effectively cover topics related to sustainability, eco-awareness, and scientific innovations.