Proteorhodospin-bearing bacteria in Antarctic sea ice
Koh, EY and Atamna-Ismaeel, N and Martin, AR and Cowie, ROM and Beja, O and Davy, SK and Maas, EW and Ryan, KG, Proteorhodospin-bearing bacteria in Antarctic sea ice, Applied and Environmental Microbiology, 76, (17) pp. 5918-5925. ISSN 0099-2240 (2010) [Refereed Article]
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.