title: Proteorhodopsin-bearing bacteria in Antarctic sea ice.
abstract: Proteorhodopsins (PRs) are widespread bacterial integral membrane proteins that function as light-driven proton pumps. Antarctic sea ice supports a complex community of autotrophic algae, heterotrophic bacteria, viruses, and protists that are an important food source for higher trophic levels in ice-covered regions of the Southern Ocean. Here, we present the first report of PR-bearing bacteria, both dormant and active, in Antarctic sea ice from a series of sites in the Ross Sea using gene-specific primers. Positive PR sequences were generated from genomic DNA at all depths in sea ice, and these sequences aligned with the classes Alphaproteobacteria, Gammaproteobacteria, and Flavobacteria. The sequences showed some similarity to previously reported PR sequences, although most of the sequences were generally distinct. Positive PR sequences were also observed from cDNA reverse transcribed from RNA isolated from sea ice samples. This finding indicates that these sequences were generated from metabolically active cells and suggests that the PR gene is functional within sea ice. Both blue-absorbing and green-absorbing forms of PRs were detected, and only a limited number of blue-absorbing forms were found and were in the midsection of the sea ice profile in this study. Questions still remain regarding the protein's ecological functions, and ultimately, field experiments will be needed to establish the ecological and functional role of PRs in the sea ice ecosystem.
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand. koh_eileen@yahoo.com
authors.forename: Eileen Y
authors.initials: EY
authors.lastname: Koh
authors.forename: Nof
authors.initials: N
authors.lastname: Atamna-Ismaeel
authors.forename: Andrew
authors.initials: A
authors.lastname: Martin
authors.forename: Rebecca O M
authors.initials: RO
authors.lastname: Cowie
authors.forename: Oded
authors.initials: O
authors.lastname: Beja
authors.forename: Simon K
authors.initials: SK
authors.lastname: Davy
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Maas
authors.forename: Ken G
authors.initials: KG
authors.lastname: Ryan
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics* / Q000378:metabolism; D000864:Antarctic Regions; D001426:Bacterial Proteins / Q000378:metabolism; D016000:Cluster Analysis; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D041965:Flavobacteriaceae / Q000235:genetics* / Q000378:metabolism; D020563:Gammaproteobacteria / Q000235:genetics* / Q000378:metabolism; D046448:Ice Cover / Q000382:microbiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012243:Rhodopsin / Q000235:genetics* / Q000378:metabolism; D025604:Rhodopsins, Microbial; D017422:Sequence Analysis, DNA; D017385:Sequence Homology
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin