Functional characterization of flavobacteria rhodopsins reveals a unique class of light-driven chloride pump in bacteria

• Main Authors: Yoshizawa, Susumu (Contributor), Kumagai, Yohei (Author), Kim, Hana (Contributor), Ogura, Yoshitoshi (Author), Hayashi, Tetsuya (Author), Iwasaki, Wataru (Author), DeLong, Edward (Contributor), Kogure, Kazuhiro (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Biological Engineering (Contributor), Massachusetts Institute of Technology. Department of Civil and Environmental Engineering (Contributor)
• Format: Article
• Language: English
• Published: National Academy of Sciences (U.S.), 2014-12-01T21:43:54Z.
• Subjects: Article
• Online Access: Get fulltext

 Light-activated, ion-pumping rhodopsins are broadly distributed among many different bacteria and archaea inhabiting the photic zone of aquatic environments. Bacterial proton- or sodium-translocating rhodopsins can convert light energy into a chemiosmotic force that can be converted into cellular biochemical energy, and thus represent a widespread alternative form of photoheterotrophy. Here we report that the genome of the marine flavobacterium Nonlabens marinus S1-08T encodes three different types of rhodopsins: Nonlabens marinus rhodopsin 1 (NM-R1), Nonlabens marinus rhodopsin 2 (NM-R2), and Nonlabens marinus rhodopsin 3 (NM-R3). Our functional analysis demonstrated that NM-R1 and NM-R2 are light-driven outward-translocating H+ and Na+ pumps, respectively. Functional analyses further revealed that the light-activated NM-R3 rhodopsin pumps Cl− ions into the cell, representing the first chloride-pumping rhodopsin uncovered in a marine bacterium. Phylogenetic analysis revealed that NM-R3 belongs to a distinct phylogenetic lineage quite distant from archaeal inward Cl−-pumping rhodopsins like halorhodopsin, suggesting that different types of chloride-pumping rhodopsins have evolved independently within marine bacterial lineages. Taken together, our data suggest that similar to haloarchaea, a considerable variety of rhodopsin types with different ion specificities have evolved in marine bacteria, with individual marine strains containing as many as three functionally different rhodopsins.