title: Proteorhodopsin in the ubiquitous marine bacterium SAR11.
abstract: Proteorhodopsins are light-dependent proton pumps that are predicted to have an important role in the ecology of the oceans by supplying energy for microbial metabolism. Proteorhodopsin genes were first discovered through the cloning and sequencing of large genomic DNA fragments from seawater. They were later shown to be widely distributed, phylogenetically diverse, and active in the oceans. Proteorhodopsin genes have not been found in cultured bacteria, and on the basis of environmental sequence data, it has not yet been possible to reconstruct the genomes of uncultured bacterial strains that have proteorhodopsin genes. Although the metabolic effect of proteorhodopsins is uncertain, they are thought to function in cells for which the primary mode of metabolism is the heterotrophic assimilation of dissolved organic carbon. Here we report that SAR11 strain HTCC1062 ('Pelagibacter ubique'), the first cultivated member of the extraordinarily abundant SAR11 clade, expresses a proteorhodopsin gene when cultured in autoclaved seawater and in its natural environment, the ocean. The Pelagibacter proteorhodopsin functions as a light-dependent proton pump. The gene is expressed by cells grown in either diurnal light or in darkness, and there is no difference between the growth rates or cell yields of cultures grown in light or darkness.
authors.affiliation: Department of Microbiology.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Giovannoni
authors.forename: Lisa
authors.initials: L
authors.lastname: Bibbs
authors.forename: Jang-Cheon
authors.initials: JC
authors.lastname: Cho
authors.forename: Martha D
authors.initials: MD
authors.lastname: Stapels
authors.forename: Russell
authors.initials: R
authors.lastname: Desiderio
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Vergin
authors.forename: Michael S
authors.initials: MS
authors.lastname: Rappé
authors.forename: Samuel
authors.initials: S
authors.lastname: Laney
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Wilhelm
authors.forename: H James
authors.initials: HJ
authors.lastname: Tripp
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Mathur
authors.forename: Douglas F
authors.initials: DF
authors.lastname: Barofsky
mesh_terms: D020561:Alphaproteobacteria / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008386:Marine Biology; D010802:Phylogeny; D010933:Plankton / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D025604:Rhodopsins, Microbial; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin