Proteorhodopsin phototrophy in the ocean

Proteorhodopsin(1), a retinal-containing integral membrane protein that fun ctions as a light-driven proton pump, was discovered in the genome of an un cultivated marine bacterium; however, the prevalence, expression and geneti c variability of this protein in native marine microbial populations remain unknown. Here we report that photoactive proteorhodopsin is present in oce anic surface waters. We also provide evidence of an extensive family of glo bally distributed proteorhodopsin variants. The protein pigments comprising this rhodopsin family seem to be spectrally tuned to different habitats-ab sorbing light at different wavelengths in accordance with light available i n the environment. Together, our data suggest that proteorhodopsin-based ph ototrophy is a globally significant oceanic microbial process.