Microbial Life > Microbial Observatories > Oligotrophic Ocean MO > Results
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Created by George Rice, Montana State University

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Figure on left is a contour plot of DOC in the surface 300 m at BATS. Note the build up of DOC in surface waters after season stratification, export during mixing then re-mineralization at depth after stratification (Hansell and Carlson 2001). Figure on right is a contour plot of prokaryotic cell abundance at BATS, showing elevated concentrations of prokaryotic biomass below the euphotic zone. The elevated biomass persists for several weeks and coincides with the periodic drawdown of DOC in the upper mesopelagic layer. Graphs provided by C. Carlson (Oceanic Microbial Observatory)

Above is an example of temporal and spatial dynamics of bacterioplankton groups in the upper 300 m of BATS in the year 2003. See contour plots in alternative format. Materials provided by C. Carlson (Oceanic Microbial Observatory)

Figure showing variation in Bacterioplankton community composition.
A comprehensive molecular approach using T-RFLP, clone library, and bulk nucleic acid hybridization supported spatial and temporal trends in bacterioplankton community composition. Increases in SAR11, marine Actinobacteria, and OCS116-related 16S rRNA fragments were identified following deep convective mixing at BATS. Bulk nucleic acid hybridization of marine Actinobacteria, SAR11, and SAR202 16S rRNAs supported T-RFLP results, as well as previous observations indicating stratification of bacterioplankton lineages in the oceans.

Clearly, picophytoplankton, which are photosynthetic, would be expected to be more dominant at the surface where sunlight is readily available. Roseobacter, while not photosynthetic itself, has been closely linked to photosynthetic algae by an ability to metabolize dimethylsulfonio-propionate (DMSP), a compound abundantly produced by marine algae. This metabolic capability would explain why Roseobacter is also more prevalent in the surface waters at BATS. Until recently, it was less clear what adaptations were possessed by SAR11a that allow it also to dominate at the surface. Sequencing of a coastal variant of the SAR11a clade has revealed the presence of a gene coding for proteorhodopsin. This protein uses light to drive the export of protons and the energy of the re-entry of protons can be harnessed to convert ADP to ATP. Still, it is unknown why these two groups are alternately dominant in the surface waters suggesting that other environmental factors other than light are important.

Copyright on all images and material by Craig Carlson and Stephen Giovannoni 2005.

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