title: Winter diversity and expression of proteorhodopsin genes in a polar ocean.
abstract: Mixotrophy is a valuable functional trait used by microbes when environmental conditions vary broadly or resources are limited. In the sunlit waters of the ocean, photoheterotrophy, a form of mixotrophy, is often mediated by proteorhodopsin (PR), a seven helices transmembrane protein binding the retinal chromophore. Altogether, they allow bacteria to capture photic energy for sensory and proton gradient formation cell functions. The seasonal occurrence and diversity of the gene coding for PR in cold oligotrophic polar oceans is not known and PR expression has not yet been reported. Here we show that PR is widely distributed among bacterial taxa, and that PR expression decreased markedly during the winter months in the Arctic Ocean. Gammaproteobacteria-like PR sequences were always dominant. However, within the second most common affiliation, there was a transition from Flavobacteria-like PR in early winter to Alphaproteobacteria-like PR in late winter. The phylogenetic shifts followed carbon dynamics, where patterns in expression were consistent with community succession, as identified by DNA community fingerprinting. Although genes for PR were always present, the trend in decreasing transcripts from January to February suggested reduced functional utility of PR during winter. Under winter darkness, sustained expression suggests that PR may continue to be useful for non-ATP forming functions, such as environmental sensing or small solute transport. The persistence of PR expression in winter among some bacterial groups may offer a competitive advantage, where its multifunctionality enhances microbial survival under harsh polar conditions.
authors.affiliation: Groupe de Recherche Interuniversitaire en Limnologie et en Environnement Aquatique (GRIL), Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Dan
authors.initials: D
authors.lastname: Nguyen
authors.affiliation: Groupe de Recherche Interuniversitaire en Limnologie et en Environnement Aquatique (GRIL), Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Roxane
authors.initials: R
authors.lastname: Maranger
authors.affiliation: Institut de Ciències del Mar, CSIC, Passeig Marítim de la Barceloneta, Barcelona, Spain.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Balagué
authors.affiliation: Institut de Ciències del Mar, CSIC, Passeig Marítim de la Barceloneta, Barcelona, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Coll-Lladó
authors.affiliation: Département de biologie, Québec-Océan, Institut de biologie intégrative et des systèmes (IBIS), Université Laval, Pavillon Charles-Eugène-Marchand, Québec, Québec, Canada.
authors.forename: Connie
authors.initials: C
authors.lastname: Lovejoy
authors.affiliation: Institut de Ciències del Mar, CSIC, Passeig Marítim de la Barceloneta, Barcelona, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Pedrós-Alió
mesh_terms: D000222:Adaptation, Physiological; D001110:Arctic Regions; D001419:Bacteria / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000032:analysis; D005417:Flavobacterium / Q000235:genetics; D009792:Oceans and Seas; D010802:Phylogeny; D025604:Rhodopsins, Microbial / Q000235:genetics* / Q000378:metabolism; D012621:Seasons; D012623:Seawater / Q000737:chemistry / Q000382:microbiology
chemical_list: D004269:DNA, Bacterial; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin