Mixing up the colors of the seas:
Phototrophy by antenna-containing rhodopsins in aquatic environments
Rhodopsin-based phototrophy is one of the two known ways by which microorganisms harvest sunlight energy. More than 50% of bacteria in the ocean’s surface contain a rhodopsin gene. Rhodopsins are defined as a two-component system (protein + retinal) that relies on the retinal to capture sunlight energy. In two exotic and rare bacteria, rhodopsins were demonstrated to bind an additional antenna composed of a carotenoid molecule that captures additional light and enhances the activity of the complex. Such rhodopsins have been known for almost 20 years, yet the isolated cases of a rhodopsin-carotenoid complex remained a curious phenomenon of marginal ecological significance.
In this project, we designed a novel workflow that uses environmental samples to pull out from a native pool of carotenoids the ones that might serve as antennas for rhodopsin. Surprisingly, using this methodology, we discovered that the ability of rhodopsins to bind carotenoid antennas appears to be widespread in nature. We demonstrate that these antennas can significantly enhance rhodopsin activity; moreover, we predict that over a third of the rhodopsins found in aquatic microbes can potentially utilize a carotenoid antenna to capture additional light energy. These antennas were neglected for almost 20 years; we now understand that they may have a substantial impact on rhodopsin-mediated phototrophy in the world’s lakes, seas and oceans.
