Functional characterization of flavobacteria rhodopsins reveals a unique class of light-driven chloride pump in bacteria.
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 S1-08(T) 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.
['Yoshizawa|Susumu|S|', 'Kumagai|Yohei|Y|', 'Kim|Hana|H|', 'Ogura|Yoshitoshi|Y|', 'Hayashi|Tetsuya|T|', 'Iwasaki|Wataru|W|', 'DeLong|Edward F|EF|', 'Kogure|Kazuhiro|K|']
D002712:Chlorides D019143:Evolution, Molecular D041965:Flavobacteriaceae D016680:Genome, Bacterial D016623:Ion Pumps D008027:Light D008969:Molecular Sequence Data D010802:Phylogeny D012243:Rhodopsin
ecology evolution photoheterotroph photoproteins retinal