O31-02 : Light-driven transmembrane H +, Na+ and Cl- pumping is mediated by three different rhodopsins in a marine flavobacterium
1Atmosphere and Ocean Research Institute, The University of Tokyo, 2Massachusetts Institute of Technology, 3Division of Genomics and Bioenvironmental Science, Frontier Science Research Center, University of Miyazaki
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 so represent a widespread alternative form of photoheterotrophy. Here we report the genome sequence of the marine flavobacterium Nonlabens marinus S1-08T. As a result, three different types of rhodopsins (NM-R1, NM-R2 and NM-R3) were found in the genome data of this strain. Functional analysis demonstrated that NM-R1 and NM-R2 are light-driven outward translocating H+ and Na+ pumps, respectively. On the other hand, the light-activated NM-R3 rhodopsin pumped Cl– ions into the cell, representing the first chloride pumping rhodopsin to be reported 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. In total, 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.