A new study led by Bluetools partners at the Technion – Israel Institute of Technology, together with collaborators from Japan, Spain, the Czech Republic, and Germany, and published in Nature Microbiology shows how some marine archaea, single-celled microorganisms found in the ocean, capture energy from a broader range of sunlight than previously thought. The research focuses on HeimdallRs, light-sensitive proteins found in members of Candidatus Kariarchaeaceae, a group of planktonic Asgard archaea.
HeimdallRs are proton-pumping rhodopsins, meaning they use light to generate a proton gradient, which helps the cell produce energy. What makes these rhodopsins unusual is their ability to bind pigments called xanthophylls, such as lutein and fucoxanthin, which they likely obtain from the surrounding environment. These pigments act as light-harvesting antennas: they absorb blue light and transfer the energy to the rhodopsin’s retinal molecule, which typically absorbs green light. This allows the archaea to make better use of the full spectrum of sunlight available in surface ocean waters.
The researchers used a combination of genetic analysis, protein expression experiments, and structural studies to understand how these rhodopsins function. They showed that multiple HeimdallR variants can bind xanthophylls and that this binding improves their light-driven proton-pumping activity, especially under broad-spectrum (white) light conditions. The structure of one of the proteins, HeimdallR1, was solved at high resolution and revealed a fenestration near the retinal binding site that enables the carotenoids to attach and transfer energy effectively.
These rhodopsins were found in samples from various marine and coastal locations, mainly in sunlit surface waters. The study also shows that light-harvesting antennas in microbial rhodopsins exist in families beyond xanthorhodopsins and proteorhodopsins, and are present in both marine bacteria and archaea.
This work also suggests that Ca. Kariarchaeaceae have adapted to life in the ocean’s photic zone through the acquisition of HeimdallRs, potentially giving them an advantage in capturing and using light energy.
📖 Read the full article here: https://www.nature.com/articles/s41564-025-02016-5