title: Light stimulates growth of proteorhodopsin-containing marine Flavobacteria.
abstract: Proteorhodopsins are bacterial light-dependent proton pumps. Their discovery within genomic material from uncultivated marine bacterioplankton caused considerable excitement because it indicated a potential phototrophic function within these organisms, which had previously been considered strictly chemotrophic. Subsequent studies established that sequences encoding proteorhodopsin are broadly distributed throughout the world's oceans. Nevertheless, the role of proteorhodopsins in native marine bacteria is still unknown. Here we show, from an analysis of the complete genomes of three marine Flavobacteria, that cultivated bacteria in the phylum Bacteroidetes, one of the principal components of marine bacterioplankton, contain proteorhodopsin. Moreover, growth experiments in both natural and artificial seawater (low in labile organic matter, which is typical of the world's oceans) establish that exposure to light results in a marked increase in the cell yield of one such bacterium (Dokdonia sp. strain MED134) when compared with cells grown in darkness. Thus, our results show that the phototrophy conferred by proteorhodopsin can provide critical amounts of energy, not only for respiration and maintenance but also for active growth of marine bacterioplankton in their natural environment.
authors.affiliation: Marine Microbiology, Department of Biology and Environmental Sciences, University of Kalmar, SE-39182 Kalmar, Sweden.
authors.forename: Laura
authors.initials: L
authors.lastname: Gómez-Consarnau
authors.forename: José M
authors.initials: JM
authors.lastname: González
authors.forename: Montserrat
authors.initials: M
authors.lastname: Coll-Lladó
authors.forename: Pontus
authors.initials: P
authors.lastname: Gourdon
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Pascher
authors.forename: Richard
authors.initials: R
authors.lastname: Neutze
authors.forename: Carlos
authors.initials: C
authors.lastname: Pedrós-Alió
authors.forename: Jarone
authors.initials: J
authors.lastname: Pinhassi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D002460:Cell Line; D005417:Flavobacterium / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects*; D008027:Light; D008522:Mediterranean Sea; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D025604:Rhodopsins, Microbial; D012623:Seawater / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D012333:RNA, Messenger; D012336:RNA, Ribosomal, 16S; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin